I have seen lots of threads on this general topic but have a specific question. It's a 2006 Explorer, Eddie Bauer, 4x4, 4.0. A couple of years ago it was throwing codes for all of the O2 heater circuits and P0403 but ran great with no problems. After extensive testing and wire repair at the O2 sensors to no avail, I replaced the PCM - Problem solved. Now it is throwing P0106, P0109 & P0401 codes at me and will occasionally not idle. In addition to the occasional bad idle, I noticed the a/c compressor would not always come on when commanded, even when it showed to be on in Forscan. The a/c compressor has even randomly come on when not commanded and shown to be off in Forscan. The occasional bad idle seems to be from a vacuum leak based on high long term fuel trim values and experience with older cars and vacuum leaks. I have searched and not found any issues with vacuum lines and suspect it is the EGR staying open at idle because it is not consistent and if I unplug the EGR vacuum lines and plug that port at the manifold the motor smooths out. I have also replaced pigtails at the EGR connector, the fuel rail pressure sensor and the MAF sensor due to the notorious wire degradation just behind the plugs. This is where we start to have fun - I replaced the EGR valve with a Standard (usually well known and reliable brand) valve and had no change, still OCCASIONAL idle issues. Replaced that with a Motorcraft EGR valve after reading several posts claiming that aftermarkets were causing problems. Still no improvement, same issues, same codes. I then put my original PCM back in - codes P0106, P0109 & P0401 went away. Of course all O2 heater codes and P0403 showed up as expected, confirming that issue was in fact the PCM because I have not seen those codes since the first PCM swap. This all leads to my question - Does this prove there is a problem in the newer PCM, as general knowledge and process of elimination would dictate, or does that P0403 code that has been in my original PCM shut down the EGR system so that it will not show the codes coming from the other (currently suspected bad) PCM? Thanks in advance for any suggestions, you guys rock!

 

Please excuse the lack of encouragement, but do you think it could be something other than the PCM ?

In the process of replacing things we move things and connections too, leading us to believe that was the problem when we were misled.

It seems when we can't explain what is happening we have the tendency to blame that little black box.

Before replacing any more parts, might be a good move to have another shop check it and see what they find, what do you think?

 

Yes, I have considered other wiring issues or something other than PCM but am at a loss to what? I have a full wiring diagram and have checked all relative wires with continuity tester and ohmeter to find no additional problems. The codes and symptoms point to bad dpfe, bad Egr or bad Egr regulator, all of which are integrated to one unit in this vehicle and I find it hard to believe I have 3 bad EGR assemblies. My current working theory is that when the wires on these plugs go bare and they short, it causes a problem in the PCM. That seems to have been the case with the previous O2 heater issue. Just thinking it’s the same issue in a different system. Any ideas on what else to check?

 

If you have the time, might be a good move to brush up on voltage drop testing.
Ohm readings will be the same if only one strand of wire is working and yet the circuit will not work correctly if it needs a little more current.

 

Update on my previous thread about probable PCM issues:
I ordered a remanufactured PCM from Rock Auto (same brand as all major auto parts stores "Cardone"). I had the new PCM installed and programmed at a Ford dealership. The car runs fine, the previous codes (P0106, P0109 & P0401) are gone but it shows a hard fault at the EVAP canister purge valve (P0466, I think). This circuit wiring has been checked by both me and the Ford Technician that programmed the replacement PCM to find no problems. We then figured we got a "bad" remanned PCM, so I ordered another. Second "new" PCM has same code. We reinstalled the original and are able to command the EVAP purge valve and complete the EVAP testing with no problems. Has anyone else had an issue with Cardone Remanufactured PCMs? I and the Ford Tech are at a loss, it is hard to condemn new parts but all signs point to the new PCMs being the problem with the new ,or at least percieved, EVAP issue.