This vehicle originally had 3 fault codes:
The EGR valve was replaced, as the shop tested it and found it to be faulty. After replacing a test drive was performed to confirm the repair. A P0405 (EGR Position Sensor Performance) returned.
To set a P0405 it takes one trip and EGR Position Sensor circuit less than 0.1 volt.
Each time the code was cleared it would return on a test drive or by running the EGR system test using a scan tool.
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.
I moved right to the EGR position sensor wiring. First I checked 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 I went to 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 I 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.
This sensor works a little different than most potentiometers. It starts high (when closed) and goes low (when open).
Using a scan tool, I ran the sensor through it’s range, the signal voltage followed along normally. My DVOM and scan tool both displayed the same voltages.
At this point everything appeared to be normal. I decided to run the system self test again. This time I noticed my DVOM and the scan tool did not match. My DVOM display 0.29 volts and the scan tool displayed 0.039 volts. This is a very large difference.
I went back to the component activation test where I have control over valve opening. The values matched again. Why would they match in one screen and not the other? Could be the aftermarket scan tool? Maybe, but I do not have to diagnose tools. 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 on a test drive.
One of two things was going on here. Either the adaptation values would not clear using an aftermarket scan tool and the battery disconnect did it or the PCM is faulty.
I waited two weeks to post this one to see what the end verdict would be and the vehicle is been fixed (confirmed with a phone call to customer). The battery reset (adaptation reset) fixed it.