Smart questions
Smart answers
Smart people
Join Eng-Tips Forums

Member Login

Remember Me
Forgot Password?
Join Us!

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips now!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

Join Eng-Tips
*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.
Jobs from Indeed

Link To This Forum!

Partner Button
Add Stickiness To Your Site By Linking To This Professionally Managed Technical Forum.
Just copy and paste the
code below into your site.

Helpful Member!  keller36 (Automotive) (OP)
9 Mar 10 15:58
Hello. I am new to the forum and had a rather extensive question. I am wondering what system is causing the sudden acceleration problems in Toyota vehicles as well as the specific part in that system, if any specific part is respoinsible. I was also wondering, depending on the system involved in the problem, whether the problem is electrical, mechanical, or a problem in the vehicle's software. Thank you for any responses.

Helpful Member!(2)  BrianPetersen (Mechanical)
9 Mar 10 17:25
Oh boy ...

If we or anyone knew the answer to that question, it would solve an interminable amount of arguing.

The short answer is that no one knows.

The slightly longer answer is that floor mats were an issue in some cases, and a mechanically "sticking" accelerator pedal may have been an issue in some other cases, but there are still an ample number of situations out there for which "sudden unintended acceleration" reports exist, but floor mats weren't an issue and the vehicles weren't equipped with the particular accelerator pedal sensor under recall.

A certain Professor Gilbert claimed to have found a situation in which the pedal sensor could be bypassed to cause a situation that looks to the car's computer like full-throttle acceleration, but Toyota hired an engineering firm which has pretty much showed that the circumstances created by the professor were all but impossible to occur accidentally in the real world. Keep in mind that you can deliberately and intentionally circumvent ANYthing if you have the right tools and experience.

That there are some sub-optimal situations in some or all of the involved vehicles, is known. Toyota has not been using an accelerator/brake interlock circuit that would override accelerator input if someone stepped on the brake. But, motor vehicle safety standards require no such system, so this is not a "non-compliance". The European manufacturers have been doing this because one of them has already had their round of "sudden acceleration" issues many years ago.

The push-button keyless engine start is a problem, because it's not readily apparent how to switch the engine off while moving.

But, there is a big elephant in the room that, for some reason, nobody wants to mention: operator error!

People stepping on the wrong pedal is every bit as much of an issue now, as it was in the late 1980's when this was a big issue the last time.

And, every single one of these "sudden acceleration" situations, even if they actually did happen and weren't the figment of someone's overactive imagination, could be stopped in its tracks by shifting the transmission to neutral.

My car has an instant engine disengagement device that is totally mechanical/hydraulic and not reliant on any software. It is called a "clutch pedal". Sadly, not too many Americans seem to know how to use one.
evelrod (Automotive)
9 Mar 10 20:04
Newest occurrence of the Toyota Syndrome lately was on the I8 in San Diego Sunday.  Gentleman went to Toyota dealer and complained but was told his Prius did not qualify. Next day on the freeway the car accelerated and could not be turned off or put in neutral, apparently.  He called 911 and a Highway Patrol unit found him and while driving along side gave instructions via the loudspeaker.  Full braking brought the speed from 94 to 55 and, it gets a bit vague here, the CHP was able to get the car stopped...Article in the North County Times/Californian on Monday.  The interview I saw later on the local news was pretty much the same story but the gentleman was NOT happy about the way he was treated by the local Toyota dealer.

I've given up on trying to figure out what is going on.  Obviously I have some ideas that others on the forum share.  I'm content, at this point, to see how politics saves the "good name" of Toyoda.


Helpful Member!  TrackRat (Automotive)
9 Mar 10 20:08
Just so the OP knows, Toyota's "issues" are several or I should say that there are several issues with Toyota vehicles and the drivers operating them.

For the record a number of accidents have been reported by drivers pushing the floor mat under the accelerator pedal. This resulted in a terrible accident in CA a few weeks back where four people were killed. Kicking the floor mat under the accelerator pedal is an operator error not a vehicle defect. People do this in many different makes of autos.

To help prevent future accidents from drivers kicking the floor mat under the accelerator, Toyota is retro-fitting their cars with a failsafe engine management system so that when a driver pushes on both the brake pedal and accelerator for more than a few seconds, the throttle is automatically returned to idle electronically, regardless of where the accelerator pedal is in it's operating range. Many car makers have had this failsafe system since cars began using Drive-By-Wire, (DBW), instead of a mechanical throttle cable.

Toyota has another situation where a limited number of vehicles have a sticky accelerator pedal. This is a defect and Toyota is repairing all cars with this problem. The problem is a mechanical one in the accelerator pedal assembly. This problem has occured in other makes also over the years.

The third issue is with the Toyota Prius hybrid vehicles. Some drivers report abnormal braking with these vehicles which use a regenerative electrical system based off of the brake system. It's complex and may or may not have a defect in it. It does operate differently than conventional hydraulic brakes and this may be what drivers are sensing? We will know more as the investigations continue.

Because most drivers have limited technical understanding of the complex computer based systems in an auto, many have proclaimed that the "black boxes" are possessed and that they take over control of the vehicle and cause unintended acceleration. This has never been substantiated and is typical speculation and lack of knowledge at work. Toyota has agreed to open the "black boxes" for all to see and has agreed to as many independent investigators as the Feds feel is necessary to confirm the only problem is with the sticky mechanical accelerator pedal on a limited number of vehicles.

Naturally if a driver crashes their car they want to blame someone else and the siren chasers are out in full force. Like the Audi unintended acceleration of the 80's I expect that when the dust settles Toyota will pay out Billions in damages for driver errors and that no one will ever be able to prove unintended acceleration happened, because it probably didn't.

Sticking throttle pedals are dangerous but the brakes will stop any modern vehicle if properly applied even with the throttle wide-open. Numerous auto industry experts have tested and conformed this on the Toyota models, so if the throttle sticks, a driver most certainly can stop the vehicle by properly applying the brakes.

The latest episode in the Toyota hysteria is a Prius owner who claims today that he Prius took off on it's own and was doing 94 mph on the highway in CA. He claims the brakes would only slow the car to 55 mph and that placing the shifter in neutral did not disengage the power to the wheels. A police officer got his vehicle in front of the Prius and had no difficulty slowing the Prius while telling the driver over a loud speaker to shut the engine off - which he eventually did. You would have thought the driver might have considered that before he called 911...
Helpful Member!  dicer (Automotive)
9 Mar 10 20:41
As a personal opinion, I feel the problem has always been electronics/programming.

I am truely amazed that the electronics systems in any device work as good as they do. But we all know about the occasional lock up of our PC's that we use daily if for nothing else comming online to sites like this.
With the ever increasing densitys of discreet electronic components, where insulation separation is in the nano world of a molecule or so, I'm really surprized there are not more problems occuring. Electronics has its place, but I think the manufacturing world is going crazy with it.
High heat, high vibration, high moisture, and dirty places are just not a good place for electronics especially when lives are at stake. I remember reading someplace on this site about the current Toyota problems and how some here said they wouldn't design a machine without a big red emergency stop button, I fully agree, problems are if Toyota did that they would most likely still have it go through a computer to shut things down. The right way to do it is cut all power to everything, but then theres another problem, the day is comming where every system in the vehicle will be electrical - electronic, and if you shut off all the power then, you would have nothing, no steering no braking no nothin, ya couldn't even open the doors or windows. Can't we see how crazy this is getting?
Things need to change, and go back to the past when reliable systems existed.  
izzmus (Automotive)
9 Mar 10 20:57
I, for one, would like to know why a button is better than sticking a key into a lock cylinder and turning it.

Some things are expected.  The pedal on the far right is the accelerator, the pedal next to that is the brake, and for some people, the pedal next to that is the clutch.  Directional control is via a somewhat vertical wheel that is rotated clockwise to go right, counterclockwise to go right.  Shift patterns are essentially standardized, with Reverse for manual shift being the only odd man out.  The control stalk at the left hand operates the turn signals.  

Why does something else similarly important (especially in an emergency) need to be different for difference's sake?

I'm not specifically slamming Toyota, here, as there are certainly other makes doing strange things to controls that should be free of question.  (Jaguar, I think, has a rotary knob shift lever that disappears into the console when the vehicle is off, for example)

I can understand the push for wanting to do away with cables and linkages and hydraulic connections.  On the other hand, the driver's air bag could be simpler if the steering wheel didn't have to rotate - it could use a compressed-gas canister instead of an explosive.   
TrackRat (Automotive)
9 Mar 10 21:33
Fly-By-Wire has worked fine for decades and that's what auto electronic management is based on. I don't think we should jumpt to conclusions that electronics or anything else is the issue until we have documentation of same. The media and others have already speculated far too much IMO. This leads to false conclusions that make lawyers very wealthy.
Helpful Member!  DanEE (Electrical)
9 Mar 10 22:00
The Prius already has the brake override function. I've tested it several times in my 2006 model to get familiarized with how it works.

With full throttle (accelerator to the floor), the initial braking is just resistance against the engine as in any car, but as brake force is increased (doesn't take that much pedal force) it transitions into a mode where the throttle starts backing off on the engine to near zero...

As you roll to a complete stop (accelerator still on the floor) engine speed will increase slightly, just enough to know it still pulling against the brakes.. but the engine is no contest against the brakes nor is it trying hard while you still have your foot on the brakes.

Take your foot off the brakes and it goes back to full throttle, since the accelerator is still on the floor..

Now the question... how many people are going to get confused with brake over-ride???  

Perhaps the safest car is the solution Jay Leno jokes about.. when you press the accelerator, nothing happens.. the car doesn't move.

MastDesgin (Automotive)
9 Mar 10 22:06
Personally I'm a huge fan of throttle cables, I'm also a enthusiast driver so I like full control over my car. All the cars I drive have a throttle cable, a key, and a clutch. I put a lot of faith in computers, I put my financial future in the hands of computers as far as work goes. But I will never trust a computer with my life (except airplanes). I go with Murphy on this one, if there's something there to fail it will. I have 3 fail safes in case of a "acceleration" problem in my cars Turn off key, Pull out of gear, Push on brakes (merc's have computer controlled brakes!!!!!).

When it comes to the Toyota issue, a simple transistor would of saved lives. all throttle signals go through this transistor when the brake is pushed it puts power to the transistor turning off the gas! Leave throttle cables on there Performance cars for power braking and Heel Toe Shifting...

TrackRat (Automotive)
10 Mar 10 10:32
FWIW, DBW cars can also be heel-and-toed as it takes a specified time for the failsafe system to cut in - usually 4-6 seconds with both the brakes and accelerator pushed.

I highly doubt the black boxes are the issue but we'll see what the investigations show. In my experience about 95.367894291326 % of U.S. drivers should not be operating a motorized vehicle because they lack the proper skills, training and knowledge which results in accidents, injuries and fatalities. Maybe all car makers should be forced to place a large label on the windshield in front of the driver stating: THE BRAKE PEDAL IS NOT ON THE RIGHT !

LionelHutz (Electrical)
10 Mar 10 10:54
Funny thing, I asked my co-worker with a new Toyota Corrolla if he's had problems with catching the gas pedal. He responds that he's stepped on both pedals 2 or 3 times when he had boots on and the car tried to take off. But then, he's sharp enough that he caught his error quickly. He did say he came within a foot or less of hitting his BBQ one time.

So, how many people would panic and just step on both pedals harder exaberating the problem?

I read one report with a table holding some of the complaints. There was a lot of complaints that basically read "as I turned into a parking spot the car took off" reported. Sounds to me they should read "as I turned into a parking spot and tried to brake I accidentally stepped on both pedals and cause the car to take off".

I've done it in my car a few times(a GM model). In those cases, I found the extra throttle would over ride the extra braking as I stepped further on the pedals and the car would not slow down. It's drive by wire as well, but I'm not losing any sleep over it acting up.
JSteve2 (Automotive)
10 Mar 10 11:09
The I8 guy did not shift the car into Neutral, and the car did stop when he hit the power button. I watched the interview very carefully for this. He claimed he did not do either of those at speed because he didn't feel it was safe at the time (I'm not judging him, either - I wasn't in his situation). You could kind of tell by the question he hadn't really thought of the Neutral issue anyway.

Most of the weird stuff is no doubt software related. There are any number of issues that can cause this - integrator windups, data value overflows, an A/D error from the accelerator signal, etc. all of which would be somewhat surprising in the abstract. However, since there is clearly an issue here, I expect that something like one of those issues will eventually be found.
dgallup (Automotive)
10 Mar 10 14:46
I don't care how FUBAR the electronics get, if the driver stands on the brakes the car will stop.  End of story.  Any accident, however tragic, is the fault of the driver.  Never the less, I'm sure there will be a bunch of ambulance chasers get rich before this is over.  People are coming out of the wood work with one crazy story after another.  It's a media feeding frenzy.  For the paranoid, how much of this is being stirred up by the government ownership of GM?
ewh (Aerospace)
10 Mar 10 16:51
Is the OP a Toyota employee? winky smile

"Good to know you got shoes to wear when you find the floor." - Robert Hunter

ivymike (Mechanical)
10 Mar 10 20:15
I don't care how FUBAR the electronics get, if the driver stands on the brakes the car will stop.  End of story.

That's a bold statement, and seems to be unsupported by facts.  I have a regular-size female friend who isn't strong enough to screech the tires by stomping the brakes in her altima - we tried it repeatedly one day - she figured it was because they were "antilock" until I demonstrated what would happen if I stomped on them.  You're telling me that she could brake hard enough to rapidly overcome full engine power, starting at speed?  I doubt it.  Then there was the case of the CHP officer who crashed... you're saying that he just hadn't thought to try the brakes?  
Helpful Member!  GregLocock (Automotive)
11 Mar 10 3:39
Admittedly if you won't push hard enough on the brake then there is a problem.

But these guys didn't really find much of an issue

"Certainly the most natural reaction to a stuck-throttle emergency is to stomp on the brake pedal, possibly with both feet. And despite dramatic horsepower increases since C/D's 1987 unintended-acceleration test of an Audi 5000, brakes by and large can still overpower and rein in an engine roaring under full throttle. With the Camry's throttle pinned while going 70 mph, the brakes easily overcame all 268 horsepower straining against them and stopped the car in 190 feet—that's a foot shorter than the performance of a Ford Taurus without any gas-pedal problems and just 16 feet longer than with the Camry's throttle closed. "

It doesn't mention what pedal pressure they used.



Greg Locock

New here? Try reading these, they might help FAQ731-376: Forum Policies

MastDesgin (Automotive)
11 Mar 10 14:42
I don't know if I'm more surprised the Camry stopped or that Camry's come with almost 300 HP... I wonder how the transmission handles it. Would it keep gearing down every chance it got or would it stay in the high gear?  
BrianPetersen (Mechanical)
11 Mar 10 15:32
If the system is seeing a full-throttle input (regardless of reason), and there's no accelerator/brake interlock (which there hasn't been, on that car), it'll keep downshifting.

The oversized engines available in North America may be part of the issue here. A Toyota Yaris 1.3 or Toyota Aygo 1.0, which are more typical Toyotas sold in Europe, doesn't do ANYthing "suddenly".
MastDesgin (Automotive)
11 Mar 10 19:22
I think at the point it kept downshifting there would be no way to stop it... you might pull it down to the next gear change then it would push even harder against the brakes and at that point brake fade would be so bad you couldn't think of stopping... now if you locked the brakes that might be a different story doesn't give the brakes a chance to fade... but then ABS comes in and might mess ya up there...
BrianPetersen (Mechanical)
11 Mar 10 19:29
One of the major auto enthusiast magazines recently demonstrated that a Camry will stop given hard brake application, even at full throttle. The problem arises if the driver doesn't press the brakes *hard* and hold them all the way until the car is stopped.

And ... you can always shift to neutral.
MastDesgin (Automotive)
11 Mar 10 19:48
I would put money that the Camry wasn't the base model with the lowest brakes, also after a few years of driving what happens when your brake fluid has a little water in it (its hydroscopic), you have changed your brakes to the cheap brand, or your not strong enough to depress the pedal enough.

there's a lot of factors that go into it, yes a 2010 brand new v6 Camry with brand new brakes and new fluid and a experienced male driver behind the wheel will probably be fine in the end. Its the few year old models that probably wont.
evelrod (Automotive)
11 Mar 10 19:54
Brian, the problem, at least with the car that had the throttle surge here in our area a while back, was the driver could NOT select neutral.  He was on the surface streets next to the dealer and was able to bring the car into the service department with the engine still surging.  Lucky guy, I guess as his problem was at very low speed.  None the less, it was not directly related to carpet or APP sensor or TPS as I was told. What does that leave as a causal factor?
I'm not going to jump to the conclusions yet, all this is still 'second hand' and/or media driven.  This very well may turn into the "Audi unintended acc" witch hunt...I hope not.  I will say, as with the Audi deal, there will be some substantial changes in the way our cars can be shut down in an emergency situation.  I'll guess a master kill switch.

ivymike (Mechanical)
11 Mar 10 20:02
have you checked ebay?  if there's not a retrofit master kill switch already there, check again next week for my offering.
70AARCUDA (Electrical)
11 Mar 10 21:00
+1, another "personal opinion" for 'unintended' software programming results/escapes, probably caused by less-than-100% testing of EVERY possible conditional condition(s).
izzmus (Automotive)
11 Mar 10 21:24
I wonder how many people have the presence of mind to realize that you can fit TWO feet on the brake pedal of an automatic.

If you can stand up, you can apply a very large amount of force to the brake pedal with both feet, especially if you're pumped full of adrenaline.
MastDesgin (Automotive)
11 Mar 10 22:05
Izzmus the problem there can be if the engines at WOT you might not have brakes, Brakes use vacuum to boost there effectiveness but if that vacuum goes away (like at WOT) then you only have 1-2 good pushes on the brake pedal before you burn all the vacuum, then even I (6'2 300ish lbs) can put enough force on the brakes to lock them (or even engage ABS). So in a panicked situation where they're trying to stop is the lay person going to know they only have a push or two?
BrianPetersen (Mechanical)
11 Mar 10 23:16
There is no automatic transmission built, that can not be shifted to neutral at any road speed and at any accelerator position.

It is a direct Federal Motor Vehicle Safety Standards violation to be otherwise.
ivymike (Mechanical)
12 Mar 10 6:26
so it would be more accurate to say "there is no... legally built, that..."

that doesn't strike me as a very convincing argument against "it wouldn't shift."
MastDesgin (Automotive)
12 Mar 10 8:08
I think we can all agree that some of the cases have been driver error, but there have been such a huge volume of them that it cant be the only plausible reason. Too bad they don't make a wrench big enough for the loose nut behind the wheel!
LionelHutz (Electrical)
12 Mar 10 8:16
Rod - Funny but I recall reading in a version of that story that said he kept shifting between drive and neutral as he drove it to the dealership. He then left it parked outside the service area with the engine racing...
TrackRat (Automotive)
12 Mar 10 10:39
Folks I can see this is getting to be a hot topic... FWIW, all of the theories were offered a couple months ago when the CA police officer crashed and there were four fatalities.

FWIW, I and others have actually tested numerous vehicles at WOT to see if they could be stopped with reasonable brake effort and all of them could including the Toyota Lexus involved in the CA accident. Most of the car mags have also conducted their own test and seen the same results.

Yes an auto trans does downshift as you are braking and yes the torque multiplication increases and yes even then you can stop the vehicle with the brakes but of course it requires more pedal pressure than normal - which is why some people report the brakes "didn't stop the vehicle". They aren't aware that more pedal pressure is required when the engine is running at open throttle.

Pumping the brakes will eventually use up the brake boost and require even more pedal pressure and that is why people are told to firmly apply the brakes and not pump them. Even at WOT all cars have a reserve of boost assist at first so the brakes most definitely will stop if applied properly. In the case of the CA accident the officer rode the brakes for miles before they finally burned out. The rotors were glowing red with sparks flying off them while he drove which confirms they were functioning. He also failed to shift the trans into neutral or shut off the ignition which proved fatal...
drwebb (Automotive)
12 Mar 10 13:43
I am also mystified that shifting to neutral, applying absolute braking force, and/or switching the engine off, or even the old 'by cable' counter measure of tapping the accelerator pedal sharply to try and jar it loose are apparently ineneffective countermeasures.  They are presumably ineffective because I hardly hear anyone saying 'if this happens to you, here's what you should do'.  Could the NHTSA know a lot more about what's going on than they are letting on?  At least with the Ford/Firestone problems they issued some PSAs reminding drivers to periodically check their tire pressure.
evelrod (Automotive)
12 Mar 10 14:08
Lionel, I think your version sounds as good as mine. Like I said, this is all media driven.

Brian, I'm sorry, but in the instances where there is NO mechanical connection with the transmission, where all control is through the ECM, failure to engage is a DEFINITE possibility.

I dislike absolutes.  I'm not too crazy about extremism's either.  I try to NOT throw a blanket over an entire industry's problems, hard as that may be.  Having built and raced cars since 1958 and been around them longer than that, I have seen "the impossible" least a couple times.

bob9250 (Automotive)
12 Mar 10 14:48
ur mom kyle.......ur mom
buddha555 (Geotechnical)
12 Mar 10 15:01
anyone know any good jokes
BrianPetersen (Mechanical)
12 Mar 10 16:40
Evel, I'm totally with you on the inadvisability of relying completely on the electronics.

But the guy who drove his "sudden-accelerating" Toyota (or Lexus? forgot) to the dealer by shifting between drive and neutral to demonstrate the problem, and countless videos on Youtube of people demonstrating what happens when you shift to neutral at full throttle on a variety of Toyota vehicles, suggests that at least by design intent, there is nothing stopping the vehicle from being shifted to neutral.

I don't dispute that there could be some sort of glitch that might be causing the engines to accelerate. But to simultaneously occur with a glitch that prevents the transmission from being shifted to neutral and prevents the ignition from being switched off and prevents the brakes from being used, AND YET the vehicle operates with all of these systems normally after inspection, sounds like a combination of things so remote in possibility that they would never happen together unless there is something deliberately causing this to happen.

A lot of parties including Toyota are defending the electronics as being more fault-resistant than mechanical systems, and I can't really dispute that. But what I can say is that programmable electronic systems are much more difficult to validate for proper operation than, say, a mechanical system, or an electrical switch that has mechanically opened contacts, or a direct mechanically operated hydraulic spool valve inside a valve body. I don't like the complete reliance on electronics for safety related systems. But it's hard to dispute that the most likely underlying cause, is driver error. (Or people abusing the system, trying to create a situation where they can file a lawsuit.)
evelrod (Automotive)
12 Mar 10 20:29
I agree that there is a lot of wiggle room in the 'honesty' dept.  Still, the volume of complaints that Greg linked us to is astounding.  Especially since they were made before the big bruhaha about the Lexus crash in San Diego.  I've always believed the "smoke/fire" cliche.  One thing for certain, we have not heard the end of this Toyota thing.  Too bad for the auto industry.  I agree with what Greg said, that it's a shame when an engineer is faulted for only being 99.9% right.

YvesLLewelyn (Mechanical)
12 Mar 10 21:09
I don't know if anybody has mentioned it - but can the electric motor/battery part of the Prius suddenly come to life unexpectedly - with or without the petrol motor? Turning off the ignition is not going to stop the electric motor. Can the electric motor be put into "neutral" or otherwise mechanically disconnected from the drive train?
BrianPetersen (Mechanical)
12 Mar 10 21:54
No, it can't. On a Prius drivetrain, the motor/generators are inherently permanently connected. Even in "neutral", all it's doing is telling (via software) the motor-generators to not deliver output torque in the direction of acceleration. It doesn't stop braking. Or at least, that's the design intent. That particular vehicle is *totally* reliant on software.

We are FAR from hearing the end of this. The problem is that as software becomes more and more complex, the probability of that software being absolutely error-free becomes lower and lower.

Should also note that Ford's hybrid system is every bit as software-dependent as Toyota's, since it uses essentially the same mechanical layout.
dicer (Automotive)
12 Mar 10 22:00
I personally have lots of experience in my little car with the accelerator sticking. It does it constantly because of the after market cruise control I installed some years back, the cause is the ball chain is too short and gets caught in the cable sheave, and there no quick cure for it.
The first time it happened it was a surprize, my reaction was to tap the pedal, and then push clutch in and key off, all with in micro seconds of each other, so yes the driver and skill plays huge in a situation like that.
 As far as brakes stopping a car with WOT and at speed, maybe with the right driver and conditions, I would think someone would have a very difficult time after getting into fade due to the heat factor, I have been into that many times in years past, its like hauling a trailer twice the vehicle weight and without trailer brakes.

If these problems are not an electric and or computer fault, then it is something commandeering the system.
I have questions, did all these cars have ABS? What other systems are run through the PCM or BCM ?  I remember hearing many years ago about ABS applying the brakes when ever without driver input, or cases where the driver hit the brake pedal and there where zero brakes.
Can the computers in these cars isolate the ignition switch?

Also I remember seeing a system that was created for police agencys, that gave them the ablity to shut off the engine fuel and ignition systems in a chase, so commandeering is not out of the question. Just curious.
GregLocock (Automotive)
13 Mar 10 7:11
I agree, a poorly maintained brake system might fade before stopping even a relatively low powered car. But I'd be surprised if a newish car suffered from that - fluid changes are presumably based on some sort of performance based requirement. If you choose to drive an unmaintained vehicle, that's fine, but cars have service requirements for a reason.

C&D's test seems like a good way of pointing out that in the general case of brake vs engine, brakes win, and EVERY car I have driven in the past month (X5, Fusion Hybrid, Edge,Highlander, assorted Australian cars) always allow you to select neutral, at whatever speed, at whatever throttle opening.



Greg Locock

New here? Try reading these, they might help FAQ731-376: Forum Policies

BrianPetersen (Mechanical)
13 Mar 10 10:55
dicer, substantially all of the involved cars have ABS (they are all moderate-to-high-end late model vehicles) and EVERYTHING on those cars except the power steering has at least some involvement with the computer system (in the case of the ABS system, it is the ABS module itself).

And therein lies the problem; complex software-based electronic systems are extremely hard to validate.
thruthefence (Aerospace)
13 Mar 10 12:12
Any of the exchanges selling "law firm" futures contracts?

I'm long "Toyota Lawsuits" if there are.
izzmus (Automotive)
13 Mar 10 13:40
YvesLLewelyn, it can't suddenly come to life any more than the engine will start up overnight in your driveway.  In many/most new cars, the ignition switch is not actually switching power on or off, it just sends a signal to a controller.

YvesLLewelyn (Mechanical)
13 Mar 10 20:40
Well it does seem that these things may suddenly "come to life" and to have a "mind of their own" - this is, after all, what this thread is about - the Prius suddenly deciding (allegedly) to speed up etc. unasked.  My thought was that the electric/battery part of the system would be more likely (and more able) to do this than the petrol bit.  
DanEE (Electrical)
13 Mar 10 22:21
I see repeated comments in this and other threads on this site about PCs occasionally locking up, with the inference that the op systems in DBW inherently have the same problem.

PC operating systems and RTOS systems used in DBW is comparing apples and oranges.

I would think that anyone who doesn't have a clue about RTOS could understand the concept of a dead man controls used on many locomotives.. You not hit button within required timeframe, train gonna stop via fully independent control system from main op control.

I first learned of same concept used in RTOS event driven code more than 30 years ago. Even your Ethernet adapter connecting your computer to a network has embedded dead man timers to kick the adapter off the network under certain circumstances.  

So far as good old reliable cable and mechanical fuel control systems that many wish for.. in my driving experience.. will I've experienced the following...

Stuck throttle run away on a tri-power 389 Pontiac
(killed it with ignition switch): check

broken cable actuated clutch pedal: check

Failed cable actuated auto transmission shifter: check

Stuck wide open carburetor secondary butterfly: check

Stuck carburetor float literally causing gasoline to pour down over hot exhaust manifold: check

Failures to date with DBW: zero.

mattsooty (Automotive)
14 Mar 10 7:05

Totally agree with you; however, I tired of this debate ages ago.....


dicer (Automotive)
15 Mar 10 19:35
DanEE, yes I think your compairing apples to oranges, I think the key word is 30 years ago. And unless you are the design engineer in charge of Toyota automotive electronic control systems, then I think you may not be totally up to par on the latest and greatest, if it was as simple as a basic RTOS system, you wouldn't see the abundance of control units placed throughout the vehicle, and complex communication protocols between them, let alone all the proprietary circuitry and software, and not to forget the closer component densitys now. And again if its not the systems failing, then it is some EM based commandeering of the system. The reasons would be obvious.  
DanEE (Electrical)
16 Mar 10 0:31
Yep, nobody can be everywhere, but one sort of gets an idea of the complexity of the design (especially if one's life has been spent in similar systems of high complexity). This is not a new problem. To put it in perspective how does the complexity of Prius System and any other DBW design compare to the design and testability required to build an Intel Core 7 processor with high yield and reliability containing 731,000,000 transistors? or NVIDIAs GPU processor with 1.4 billion transistors? or IBM Blue Gene Supercomputer with up to 16 cabinets, with each cabinet containing holding 1,024 compute nodes.

The DA systems behind these complex products would be above all things, the most interesting to see first hand, but understandable that this has alway been the most guarded of intellectual property.    

Although there are a lot of specifics marked as proprietary and not disclosed in FSM Volumes 1 through 4 approximately 5000 pages for the Prius (my 19 pound collection of volumes only for the 2006 model, sorry), does remarkably disclose a tremendous amount of information on the monitor strategy, enabling conditions, malfunction thresholds, and fail safes in the system. I find the 471 page ES (Engine Control System) section in Volume 1 a particularly interesting read and also the 569 page HV section (hybrid control) in volume 2. btw I count 5 major processors on the BEAN bus and another 5 on the CAN, but I guess that depends on the defintion of major versus minor. Anybody can buy these documents for about $610.22 including tax and shipping :<)

The Oak Ridge National Lab tear down study published about 4 years is quite revealing on the electro-mechanicals but doesn't touch upon control except in the most basic aspect.

One of Toyota's patent descriptions on the power demand/energy storage/control algorithms is 92 pages long, and a good concept description. Compare to most, 4-5 concept pages seems typical.

I agree RTOS systems aren't so simple, nor are they the only technique, many favor Finite State machines implemented in program logic arrays as a simpler more verifyable design. Interesting to read a bit on Wind River Systems development of the Common Core System for the Boeings 7E7 Dreamliner and here on some of the work going on.   

So far as the "must be EM theory", I think the level of discussion in this engineering forum could be more fruitful if it evolved more toward specifics on the standards and test practices and whether they are adequate.  Anybody close to and a bit more up to date on the list of generally used automotive EMC/EMI standards and test practices than below?

CISPR 12 IEC Global X Radiated emissions and immunity 2001
CISPR 25 IEC Global X Radiated immunity 2002
ISO 7637 ISO Global X Transient immunity 2002
ISO 10605 ISO Global X X ESD 2001
ISO 11451 ISO Global X Radiated immunity 2001
ISO 11452 ISO Global X Radiated immunity 2002
SAE J551 SAE North America X Radiated emissions and immunity 1995
SAE J1113 SAE North America X Radiated emissions and immunity 1995

How would these or current standards compare for example to the applicable sections of Mil 461-E? or the standards that were used to test the Boeing 757 FBW and documented in the  NASA/LLNL FBL/PBW Program Boeing 757 HIRF Test Plan?

The latter is not so out of line as cars driven in close proximity to some of the ground facilities used in testing the 757 e.g. Greenville, NC VOA station or Wallops Island Delaware or similar facilities could receive similar exposure levels..

I guess a major point of this post is a lot of what is being put in vehicles these days and seen with controversy  has a very long predecessor history in related fields. And in engineering, many times the answers can be found outside one's own sandbox.    
Dan320 (Aerospace)
16 Mar 10 7:36
Good joke.. I don't know.. How about: My Toyota is Spastic?
Ultraworld (Automotive)
16 Mar 10 18:49
I watched a woman recently testifying before the house on the 6 terrifying minutes her Camry went berserk, speeding away while she was helpless to stop it. She did manage a phone call to her husband to say goodbye, but she couldn't put the car in park or just turn the car off. I really feel GM (Government Motors) is just pushing this into the forefront to improve sales of American cars. And it has helped them.
mattsooty (Automotive)
17 Mar 10 16:33

Basically, when you are up against people whose only rational argument is 'well I hate DBW because I want to be in control of my vehicle' you know you might as well be conversing with somebody who is straight out of Nottingham in the 1810's and a follower of King Ludd....


TrackRat (Automotive)
17 Mar 10 22:16
Well now we have a CHP officer claiming in his seven page report that Mr. Sikes was pressing hard on the brakes and the vehicle would only slow to 85 mph... The CHP officer knows this because he saw the brake lights on and what appeared to be Mr. Sikes pulling himself up with the steering wheel as if he was using all of his body to apply the brakes.

The CHP officer observed all this while driving at 90 mph next to the Cosmic Ray, Satan, Space Alien possesed Prius. The onboard black box data recorder and independent nhtsa engineers who inspected the Prius didn't find anything to support Mr. Sikes claims.

Wasn't their a CHP officer involved in a fatal Lexus accident a few months ago?
hemi (Automotive)
18 Mar 10 0:20
"Basically, when you are up against people whose only rational argument is 'well I hate DBW because I want to be in control of my vehicle' you know you might as well be conversing with somebody who is straight out of Nottingham in the 1810's and a follower of King Ludd...."
Many of us have been on both sides of the DBW equation.  No doubt, when you are creating a system for use by semi- or unskilled users, DBW allows many otherwise external and unpredictable parameters to be internalised and constrained within known and reasonable boundaries.  From the user's perspective, however, his freedom to control the device has been limited, and in comparison to a non-DBW system, to an unreasonable degree.  Having been on both sides of this, I am very sympathetic to both points of view.  For a typical user, DBW is a better solution than direct mechanical control, whether they like it or not.  On the other hand, a user such as Evelrod would never be well served nor satisfied with a typical constraining DBW system aimed at typical users (jetfighter FBW systems, for one counter-example, are a different story, to be sure).
DanEE (Electrical)
18 Mar 10 8:09
mattsooty (Automotive)
18 Mar 10 14:14
'On the other hand, a user such as Evelrod would never be well served nor satisfied with a typical constraining DBW system aimed at typical users (jetfighter FBW systems, for one counter-example, are a different story, to be sure).'

I'm not sure quite how anybody would know the optimum position for the throttle in consideration of dual independant cams, valve lifts, swirl valve, intake tuning valves etc etc.....

evelrod (Automotive)
18 Mar 10 14:54
I have no problems with a DBW system of throttle control...I DO have a problem with ALL controls handed over to the ECM leaving me with the 'hope' that all this 'video game' stuff will work the way it is supposed to (and often does NOT).

For the very same reasons, I do not like ABS on a race car.  ABS simply CANNOT out brake me on a racing circuit...Indeed, ABS that I have had on a racing circuit have "given my heart a jump" on occasion....Not good for an old man, that's for sure!

I'm not anti tech. I am anti 'stupid driver', which, in my humble opinion (yeah, right), is the biggest problem with unintended acceleration in any car. Is this a uniquely American problem?  

ivymike (Mechanical)
18 Mar 10 14:55
well sure, as noted above (I think) the forners don't have any power under the hood.
mattsooty (Automotive)
18 Mar 10 16:48

I hope you didnt think I was having a dig at you personally - I most certainly was not.

Just please dont start shouting: -

"I DO have a problem with ALL controls handed over to the ECM leaving me with the 'hope' that all this 'video game' stuff will work the way it is supposed to (and often does NOT"

Some of us have more 'career' in front of us rather than behind! winky smile

I guess my point is, in this consumer driven world, people want their cake, to eat it & not get fat. Which is why all these fancy engine technologies arise in the first place.

The difficulty is that all of these technologies, when brought together, simply cannot be controlled by the main input as throttle plate position. That is why DBW is now pretty much  de rigeur. And technology is not standing still to let people catch up either.

Sure as night follows day a racecar with simple control systems, when properly driven, is as pure a form of driving as one can get - however, this set up is only good for one scenario, one car, one driver, one event and F all use on the street or in real life. Not only that you wouldnt be able to sell it for use on the street in most of the world.

TrackRat (Automotive)
18 Mar 10 20:52
More proof of driver error, not a vehicle defect, that resulted in a Prius crash.
berkshire (Aeronautics)
18 Mar 10 21:43
Interesting comment buried in that article.
Any truth in it?

"In a report earlier this month, The Associated Press found that for years, Toyota has blocked access to data stored in the "black boxes" that could explain crashes blamed on sudden unintended acceleration. "

JSteve2 (Automotive)
18 Mar 10 23:28
It's true, but it's been true for everyone. Those black boxes are a litigation Pandora's box, and it's not just about the car companies. Drivers, vehicle owners, insurance companies, fleet owners, and just about everyone else have been mulling over whether opening those boxes are good or bad for them. Further, they don't store a lot of parameters, they don't store them at a high sampling rate (except possibly in a rolling buffer of a number of seconds that gets captured immediately after a noteworthy event), and they could actually make understanding a problem more difficult rather than less, if the limitations of the information provided were not well understood.

The fact that Toyota has not resolved this issue is no indictment, because they would be the first. Just call your (fill in the name) dealer and see if you can get the data downloaded from your car and you will see what I mean.
TrackRat (Automotive)
18 Mar 10 23:35
What they mean is Toyota like most auto companies does not allow others to access their black boxes. If there was evidence or potential evidence of Satan, Cosmic Rays, or Ray Charles taking over control of these Toyotas and racing them down the road, I'm sure the lawyers will gain access to the black boxes.

Toyota said weeks ago that they would open the black boxes for all to see and as far as I can tell they have done so. That's how they determined this woman was not pressing on the brakes but instead was actually pressing on the accelerator. Same deal with the 94 mph runaway Prius in CA. The black box showed no effort to stop the vehicle, just light pressure on the brake pedal 250 times...

NHTSA engineers are the ones making these public reports so it's not Toyota, it's an independent group of experienced crash research investigators and engineers.
dgallup (Automotive)
19 Mar 10 9:44
I will never own a car with one of those black boxes.  Perhaps that means I will never own another new car but so be it.  I have no problem with DBW, ABS, traction control, stability control, etc. but I will not let my car testify against me in court.  They can't make a wife testify against her husband, why should my car be allowed to testify against me?  They have already used those black boxes in a number of high profile court cases, the precedent was set long ago.  
NormPeterson (Structural)
19 Mar 10 11:48

With all due respect to those looking forward to a long and fruitful career in vehicle controls, my own feelings run closer to Rod's.  I don't think there's anything intrinsically wrong with DBW either, though the calibrations developed to suit the driving public at large may not be as good as they could be for high performance driving.

I'm a little familiar with recalibrations done to the current Mustang PCM, generally to suit the drag racers and street-driving dragrace wanna-be's.  Quicker rates of throttle opening and elimination of a little dead-band just off zero pedal seems to be the direction that most take.  As far as I'm concerned, that's off in the wrong direction if throttle modulation while cornering is what you're after.

The calibrations for other systems may likewise not favor performance driving.  If they're set too conservative to suit less capable drivers, they can get in the way of drivers who possess better skills.

It may be that "video game" generations will have an easier time adapting than those of us somewhat "senior" folks.  In some cases, it becomes a matter of having to unlearn skills that have served well for 40 years or more and replacing them with new approaches that vary from slightly contradictory to completely so.  Even though I know intellectually what might be going on, I can't predict precisely how I'll cope with whatever somebody else has determined that my vehicle should be doing instead.  I have come to expect certain "linearities" (curvilinearities?) while driving, and don't like being caught by surprise.

By way of postscript, my wife just drove the latest addition to the vehicle "stable" home last night.  A Subaru 2.5GT Limited.  Lots of power, lots of features, DBW, ESC, ABS, and brake assist that I know of.  It's too soon to tell much, other than it being possible to shut the ESC off.  The jury is still out on brake assist - if it isn't better than I am, its value is questionable, and if it is then I might get hit from behind.

One other thing - it has a clutch with which to deal with any unintended acceleration.  Her choice, and strongly so having driven MT cars virtually exclusively for 40 years.

LionelHutz (Electrical)
19 Mar 10 13:15


The black box showed no effort to stop the vehicle, just light pressure on the brake pedal 250 times...

TrackRat (Automotive)
19 Mar 10 16:03
The Source was NHTSA and Toyota who with others inspected the data from the black box.
LionelHutz (Electrical)
19 Mar 10 16:19
And yet the stories I've read said the Toyota "black box" will only record about 5 seconds before and 1 second after an accident. There was never an accident to trigger saving a recording and if it still holds 5 seconds of rolling data then the stored events while at 90mph on the road were long gone by the time the car was stopped. I've yet to read a creditable source that actually explains what the Toyota recorder is capable of and how it was able to record those 250 brake presses.
evelrod (Automotive)
19 Mar 10 16:25
"Black box"?  Child's play!  In addition to 'master shut off' I can see a 'real time' monitoring of individual cars via the "On Star" or similar program being made mandatory.  Man, if that's no Orwellian I don't know what is.  Yeah, I'm way to old to accept all this as "normal", but I suspect the newest generation of 'video gamers' will treat it as 'ho-hum'.

thruthefence (Aerospace)
19 Mar 10 21:14
A "true crime" story from the trailer parks of Louisiana:

Local Sheriff gets "Onstar" heads-up call, reporting an accident in the Piney woods of North Louisiana. Unable to contact registered driver, the worst is feared.....armed with GPS coordinates provided by big brother, er, Onstar, the cops arrive at the Escalade, in a ditch, stuck up to the axles of the formerly shiny "22's" in red clay.

Further detective work reveals driver "Asleep at the wheel", open containers, two comatose co-perps, a sixteen year old girl, and 1/2 oz or so of reefer.

"Oh brave new world that has such people in it"

The adults are now safely ensconced on the 'Pea farm' not able to make bail, the girl returned to her parents.

No mention if the Escalade had unintended acceleration, and ended up in the ditch. I would bring up that possibility to my court appointed attorney, I think.
GregLocock (Automotive)
19 Mar 10 21:43
Wasn't he 250 brake presses from a Prius? The hybrid unit's controller has a much longer memory than the usual black box.

Incidentally throttle pedal progression is a designed parameter even in cars with mechanical linkages, for instance compare a Merc and a Ferrari.



Greg Locock

New here? Try reading these, they might help FAQ731-376: Forum Policies

NormPeterson (Structural)
20 Mar 10 10:16
I'm sure, Greg.  Could make relatively low powered vehicles be perceived as being more powerful than they really are (thus favorably impressing prospective buyers on the test drive and hence benefitting sales).

Or in the other direction (with a very specific individual example here), the 'before' and 'after' arrangement going from a carburetor-style cable throttle actuation vs a sector whose arc need not be circular nor whose instantaneous center need never be concentric with the throttle plate shaft.  Made a significant improvement in the driveability of an aftermarket multiport EFI equipped (58mm x 2 throttle body) SBC-powered autocross car.  Even in normal street use as well.

TrackRat (Automotive)
20 Mar 10 11:07
For years Audi and VW - especially on the Turbo cars used a very progressive mechanical throttle to give the impression the engine had much more off-idle power than it really did. It definitely improving normal driving and compensated for the lack of off-idle boost.
dgallup (Automotive)
22 Mar 10 10:41
The ill-fated Oldsmobile diesel got to about 90% fueling in the first 25% of "throttle" pedal travel.  Still didn't feel responsive.   
TrackRat (Automotive)
22 Mar 10 13:22
Beating a dead horse don't make it faster or stronger. <LOL>
thruthefence (Aerospace)
31 Mar 10 8:40
Have there been any issues with pick up trucks?

I don't recall any.

Wouldn't the technology be similar?
BrianPetersen (Mechanical)
31 Mar 10 17:50
Some of Toyota's pickups have been included in the recalls. The engine control technology is the same and the strategy used for the accelerator pedal sensors is the same and the same suppliers of those parts are used.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!

Back To Forum

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close