One of our favorite shops was up against the wall with this one. Time spent diagnosing, parts installed, and fault codes returning. Let’s take a look at how we worked through the problem.
A Chrysler 300 was brought into the shop with three fault codes:
- P0404 EGR Solenoid Circuit
- P0405 EGR Sensor Circuit Low
- P0406 EGR Position Sensor Performance
The exhaust gas recirculation (EGR) valve was replaced, as the shop tested it and found it to be faulty. After replacing the part, a test drive was performed to confirm the repair. A P0405 (EGR Position Sensor Performance, circuit low) returned. This was one of the three faults previously set.
To set a P0405 it takes one vehicle trip and an EGR Position Sensor circuit signal less than 0.1 volt. Each time the code was cleared it would return on the initial test drive or by running the EGR system test using the MVDS GScan software. This should make it easier to diagnose as the problem is present at all times.
During the EGR system test the engine practically stalls. This indicates the EGR is working mechanically and electronically (since is it a linear EGR valve). The PCM can open and hold it open. No need to check that circuit right now.
The technician on the other end sent me a photo of the wiring and his results to confirm he was on the correct terminals.
I asked the technician to move right to the EGR position sensor wiring. First I had him check the sensor ground at the EGR valve and PIN 27 on connector 2 at the PCM. It was 0.01 volts and reacted normally when loaded. Next was the 5 volt supply at the EGR valve and PIN 27 on connector 1 at the PCM. It was also good. Next up was the sensor signal wire. Once again he tested it at the EGR valve and PIN 22 on connector 2 at the PCM. It was when the valve was in the closed position and matched what the scan tool displayed.
Once again, the great thing about the MVDS and the Autologic Support System, when I am helping a technician, he or she can send me photos, screenshots and even allow me to take over their MVDS tablet to perform the tests virtually, right from my desk. here's an example of a photo he sent to show me his some of his test results.
This sensor works a little different than most potentiometers. It starts high (when closed) and goes low (when open). Using the MVDS tablet, we ran the sensor through the full range, the signal voltage followed along normally. The DVOM and scan tool both displayed the same voltages.
At this point, everything appeared to be normal. I decided to have him run the system self-test again. This time I noticed his DVOM and the scan tool data did not match. The DVOM displayed 0.29 volts and the scan tool displayed 0.039 volts. This is a big difference.
We went back to the component activation test where we have control over valve opening. The values matched again. Why would they match in one screen and not the other? Could be the scan tool? Maybe, sometimes data gets skewed or its a software issue. I thought about my options and poked around the system a bit more. Nothing popped out on the fault code definition or flow chart. I decided to reset adaptations using the scan tool.
Once adaptations were reset I ran the system self-test again. This time it took did not set the fault. To confirm I went for a test drive - The fault returned. Almost there I thought. I decided to disconnect the battery for a few minutes. After about 15 minutes I connected the battery and ran the test again with my DVOM and scan tool connected. The sensor now read 1.4 volts.
After wiping the PCM's memory clean a new voltage value was present and the fault code did not return with using system test or during a test drive. One of two things was going on here. Either the adaptation values would not clear using a non-factory scan tool and the battery disconnect did it or the PCM is faulty.
The shop sent the car back to the customer and asked they return in two weeks to recheck the system. The vehicle was brought back in, no fault codes and the EGR system was functioning normally. The battery reset (adaptation reset) fixed it.