How to fix the U0168 Code on a 2007 Toyota Camry Hybrid?

[yamoffathoo]

I was investigating why the A/C System was not cooling and performed the following test after measuring no connectivity between any of the HP sensor pins, 5V on two of the A21 sensor connector pins and 28 psig at the LP A/C port:

- Turned the A/C switch on with blowers on high and temperature on low
- Connected four 1.5V batteries in series with +ve to terminal 3 and -ve to terminal 1

The A/C blower and indicator lights immediately stopped functioning
The Main and Sub fans both began spinning.
Removed the testing rig and replaced the A21 sensor connector
Powered OFF/ON

No A/C blower or indicator lights
Main and Sub fans both spinning
U0168 Code detected - no others.

My mistake was imposing 6V instead of <5V across the A21 sensor (per attached).
Is there a way of recovering from this error?

 

[3DDave]

The short answer is to find someone who knows how to diagnose this system and figure out which module you probably killed.

See also https://dot.report/dtc/U0168

 

[BrianPetersen]

U0168 = "lost communication with vehicle security module"

This has to do with your security alarm / immobilizer system, nothing to do with the air-con.

But, network communication faults can cause all manner of havoc with anything else on the network.

How did you scan it for fault codes and with what? The U0168 appears to be an engine-control-module code. A lot of simple+cheap code scanners (Scangauge etc) only look at the engine control module and won't scan the whole network (incapable of doing so). A good scanner will show you the network topology and which control modules are active, and can show you faults set in any of them, and display input-output status and test output devices.

I do not know if that particular car has a "smart" network-connected climate control system, or an old-skool "dumb" system that can only be diagnosed with physical tests and measurements (like what you are attempting to do). That the troubleshooting document linked to above is explaining DTCs associated with climate control, suggests that it is a "smart" network-connected system. Most newer vehicles are like that.

If it has a "smart" system, there is still a place for doing the physical tests, but it's only after seeing what I/O the computer is seeing, and identifying which input or output is causing trouble (and if it is a wiring or sensor related issue, the control module probably already knows and probably already has a fault code set)

 

[3DDave]

It's a Toyota Hybrid - it's going to be filled with microprocessors.

I wonder what batteries were used and why 4 when it clearly says 3 and if the 6V is the measured voltage or just calculated based on the nominal voltage and the number of cells.

Was the voltage applied to the sensor or to the connector (A21) that attaches the wire harness to the sensor?

5V on two of the A21 sensor connector pins - You cannot have voltage on a pin. You can only have voltage from one point to another point. What was the other point? 3->1 should be 5 V when powered by the amplifier. 2->1 should be between 0.5V when there is no pressure and 4.8V when there is 3.187MPa.

To do step 5, INSPECT AIR CONDITIONING PRESSURE SENSOR, requires a refrigerant pressure gauge to measure the pressure of the refrigerant and see if it matches the voltage output.

Perhaps some other wire has been cut or disconnected as part of whatever else was being investigated.

The A/C compressor might be as shown here - the OP is leaving out all the important information.

Interesting video on failure to cool due to a flow sensor failure; diagnosed with a magnet (does not appear to apply to hybrid models):

 

[BrianPetersen]

The FIRST diagnostic step on ANY network-enabled vehicle (includes this one) is to scan the system for codes with a GOOD scanner that is capable of scanning ALL of the control modules on the network ... not just the engine control module.

The SECOND step, having identified relevant fault codes, is to use a GOOD scanner (the same one) that is capable of displaying live data from ALL control modules, and using that to display the measured values or status of the parameters that are relevant to the fault codes identified.

If the original poster's voltage mix-up broke A21, the on-board diagnostics will identify that.

Bear in mind that having the vehicle power-on with anything unplugged, or disconnecting the battery, is going to introduce spurious power-loss codes. So, at this point, the thing to do is plug everything back in the way it's supposed to be, scan the entire network for codes, save the report (good scanners can do this), clear all codes, and scan the entire network again to identify current codes. If A21 didn't survive the wire-poking episode, it'll immediately trip a code. If it did survive, it won't, and you'll be able to go into the measuring-blocks section of your scanner and see what data the sensor is reporting.

A21 probably didn't show connectivity between any of its pins because it is a sensor, not a switch, not a relay. None of its pins are physically connected (via copper or physical contacts) to any of its other pins, so there's no connectivity. Depending upon how the sensor works, it may or may not display resistance values between some of its pins. Applying voltage to where it isn't supposed to be, is a good way to let the magic smoke out of such devices.

The scan tool will reveal whether A21 still contains its magic smoke in a way that produces a valid sensor reading.

 

[3DDave]

A21 is the connector. It's probably fine, unless fat wires were used to probe the connections on each end of the cable and over-expanded any sockets. It's connected though the cable to the amplifier, which may or may not be fine. Toasting part of the amplifier is unlikely to set a specific code and may report other modules have failed. Unplugging may produce no-communication codes.

The fun part is that the pressure sensors from Toyota seem to range from $200 to over $300. Genuine Toyota amplifiers are about $900, though I can't tell if they still have one for the 2007 Toyota Camry Hybrid available.

There's an electrical circuit in the sensor; all the pins are connected to each other, though the impedance to current flow may be very high. I expect that more than a few milliAamps flows into pin 3 and out of pin 1 at the correct 5V supply.