PCM Failure? - 2001 Sierra 1500

[Jman45]

Hi,

 

I have a 2001 GMC Sierra 1500 with a 5.3L V8 that I think may be having PCM issues. I initially got an intermittent CEL for P0327 and P0332 low input knock sensor codes on bank 1 and 2. The truck otherwise ran fine over the course of 500-600 miles with the codes randomly popping up a couple of times. Soon thereafter I got a CEL for a P0300 random misfire and started getting a rough idle and was also having erratic shifting issues (jerky 2-3 shifts, engine revving out in gear before shifting to next gear, etc.). I parked the truck and began diagnosing things. The computer also had P1639 & P1635 5-volt reference codes in it. I began checking the coils and tested spark with an HEI Ignition tester and found all cylinders had good spark. Next I checked the 5-volt reference at the TPS which is where things get a little funny. The power circuit that is supposed to supply 4.5-5 volts is supplying 8.5-9 volts. Testing the throttle position signal circuit, which I believe should read between .5-4.5 volts, is actually reading between 1.22 volts with the throttle closed and 7.8 volts at wide open throttle. I swapped the TPS with a known good unit and am getting the same results. I checked the wiring harness to the PCM and see no damage or anything out of the ordinary. My next step was going to be a check of the fuel pressure sensor circuit at the fuel pump assembly, but now after several startups with all the same codes, I am getting P0335 & P0339 crank position sensor codes and have a no start condition.

 

At this point, I suspect that the PCM has failed as I find it highly unlikely for all of these issues to happen simultaneously. That said, does anyone have any suggestions on what else I can check before dropping money on a replacement PCM?

 

Thanks,

JC