Possible PCM failure? 05 Ex 4.6

[DrCheeto]

So I've been battling a p0620 and erratic "check charging system" errors. I had replaced the alternator, the pigtail, and even ran a new wire to the PCM.

Using my scan tools (Handheld scanner, and ELM327 with torque pro), when this would happen, the PCM would sense 9.0v or 22.0v - Probing the wire at the PCM would yield 13.5v, as would probing the battery, so the alternator was obviously not the culprit here.

I was just ignoring this for the time being until I could do further troubleshooting before popping 200+ on a reman PCM - However, yesterday I was driving back from somewhere and went to pass someone and experienced a misfire and a huge power loss. I pulled codes and got a P0316, P0303, and P0620. At first I assumed a coil had failed, but this was running much, much worse than just a single cylinder misfire, it almost sounded like it had jumped timing (It hasn't. If you turn the car off and on it runs fine for a couple of seconds).

I cleared the codes and then re-pulled them immediately and got a long laundry list of codes that were completely different than the previous set (See picture). Codes were : P0300 (Random misfire), P0307 (Cyl 7 Misfire), P0308 (Cyl 8 Misfire), P0316 (Misfire detected at startup) - This code set itself without ever experiencing a start cycle, P2196 (02 Bank 1 Sensor 1 stuck rich) , P2197 (O2 Bank 2 sensor 1 Sensor Signal stuck lean), P0620 (Generator circuit fault), and P1000 (This code has always been there recently, even after all readiness monitors are completed.)

I also noticed the MAF voltage was reporting 1.3-1.6v at idle, which is super high. It was too cold out last night for me to probe it with a multimeter, but when I disconnected it and started it , it did the same things in Fail-Safe mode. Idles perfect and continues to degrade the longer it runs.


I can't imagine all this failed at once, but i'd hate to waste 200+ on a computer to find out it's something else. I've checked the harnesses for any damage, haven't found any. Just wanted to post here to see if anyone had any ideas before I pop for a PCM.

Thanks!

 

[h82loseejr]

Go to youtube and watch SCANNER DANNER he has a good video on a "chevy cobalt" on diagnosing bad PCM....different car but same theory and steps apply....do all of the things he talks about before saying bad computer

 

[imp]

@DrCheeto
PCMs occasionally do prove faulty, but not often. However, given what you wrote, and being aware that the PCM nowadays functions in correlation to Voltage Regulation output of the Alternator, I'm leaning towards a PCM voltage regulation fault. imp

 

[h82loseejr]

Nothing replaces a proper diagnosis with the proper tools. Faulty wring corroded connectons and or chafed wires are hard for a home mechanic to diagnose....A scope is almost mandatory to be able to properly diagnose any modern vehicle. I do have one myself but most do not...Too often home mechanics say "its the brain" Its the computer" when in fact its is not even remotely close to it....The thing is to do a proper diagnosis of a bad PCM would include checking every system that is affected outside the PCM...Components and wiring included not just "I have a code that part is wrong"

 

[h82loseejr]

I Promise you that a ELM adapter form ebay and Torque app will not get you to 'MY PCM IS BAD"....IF you come to that conclusion based on these tools then IF AND I DO SAY IF....you are correct it is by sheer luck....and nothing more....

 

[h82loseejr]

After learning what i have about vehicles andy ELM 327 adaoter us good for nothing more than extra gauges on your phone...codes mean very little in an actual diagnosis of a vehicle...they give you ONE....ONE clue in where to start....Like i said watch that video of Scanner Danner on Youtube as a matter of fact here is the link.......""....Unless you have the factory (or any proper michell system or other) wiring diagram and have done every step in this video there is no possible way that you can say "my computer is bad" with any kind of knowledge behind your statement