2001 4.3l 4dr 4wd. Chasing an apparent short to ground. When checking continuity on wires from MAF sensor, I have a short between the pink 12v wire and the blk/wht ground wire. Also found this same short in several other sensors. Truck has been running good and bad, transmission has felt erratic but could be engine making it feel that way. Gas mileage has been dismal. Only DTC set is P0300. Truck feels like it's low on power and stumbles at light load on flat road, give it a good kick and it will drop to third and it runs like it should, until you back out of it. Check engine light flashes while under light load, but stops under higher load, downhill vs uphill.
New parts include:
cap, rotor,wires and plugs (all AC Delco)
O2 sensors(bosch)
New crank position sensor( Can't do a relearn because of sensor issues).
Scanner only shows a P0300 set. Pending codes are P0300, sometimes mass airflow sensor low. History codes vary between 20-30 codes, mostly relating to O2, air injection, evap and various transmission codes, although never the same after clearing.
I'm almost 100% sure its a wiring issue When checking continuity between different wires, I get a short or continuity between wires that don't make sense from looking at wiring diagrams. While checking wires, all connectors are disconnected from all sensors on harness.
Any ideas would be great.

 

P0300 by itself is not a MAF sensor issue. If you had a short or a MAF sensor issue there would almost certainly be other codes.

If you want to really do diagnosis, begin by checking your cam sensor retard and repair if out of spec Should be 0 +/- 2 degrees.

 

The MAF is good. it's the wiring to the MAF that has me confused. With the connector disconnected, checking continuity to ground, I have blk/wht wire 0 ohms to chassis ground, Pink 12v wire is also 0 ohms to ground, and yellow signal wire has no connection to chassis ground. This same set of tests also occurs on other sensors. The pink wires should be 12v supply wires and not have a dead short to ground. Unless I'm not understanding or testing wrong, somewhere I have a connection between wires that isn't meant to be and could be the cause of my issues with the truck running weird. All my testing has been done with the harness disconnected to eliminate sensor or other components, basically end to end of wires only.
In my original post I noted that only a P0300 had actually set and turned on the CEL. Pending codes were usually P0300 and one for the MAF reading low. History codes are all over the place and change each time cleared. This leads me to believe I have a short in my wiring harness.

 

Black/white is ground for MAF sensor. If you check this circuit to chassis ground with the MAF sensor disconnected you will get 0 ohms.

Pink is 12V from ECM1 fuse. It should have 12v when ignition is in start or run position. Other things draw on this same circuit, so continuity to ground is irrelevant and thus an inappropriate test. If it has 12v with the key on you are golden. If not check the fuse.

 

Ok, after further testing, I am now wondering how, what, and where I have a data signal loss to the PCM. Didn't find any burnt or chafed wires, all grounds are clean and making good connection. Reason being is when scanner is hooked up , most if not all codes in history are pass/fail type codes. Somewhere during startup the computer is losing connectivity with almost all system modules.


There is no way This is right. These are the codes I have pulled from the ECM. Each scan gives about 40 codes, some show up each time, others are random. No two consecutive scans are the same.

 

Clear all the codes in history and current. See what sets again - report. Also keep in mind that maybe scanner might be in error with all that!

 

This list is a compiled list of all codes that showed up after clearing a half dozen times. Two different scanners, Bluedriver bluetooth and an Innova 5160rs. Not every code happened every time, only about 40 at a time. But as I said they change with each clearing and scan.First noticed this after crank sensor change trying to do a relearn. Scanner won't do the relearn because of these codes being present, or at least because one or more are present it doesn't like. Only consistent code and one that sets CEL is P0300 random misfire which was caused by the crank sensor replacement.Today I finished checking the wiring harness for a damage, swapped in a known good PCM. Same issues. Corrupt data is my conclusion so far, as to where and what is causing it, is where I'm at. The truck idles great, but stumbles bad above idle. It has kind of went from running good to running real bad over a week or so. I'm pretty good at keeping these things running good(I have 3 of them currently) but this one is testing me.

 

Not sure how you can swap in a known good PCM unless it has been programmed for your vehicle. Passlock should keep it from starting.

Best wishes and hopes for a successful repair.

 

The only thing that I have found vehicle specific with the PCM is passlock. It's paired with the vehicle key. That is able to be changed fairly easily. Engine management is the same as long as it's the same engine. From what I gather digging around in tech manuals and talking with GM techs, the computer is actually the same for all motors, It looks for specific inputs and uses them to determine what set of instructions to use. So if a v8 computer was put in the same year v6 vehicle it would ignore the 2 missing cylinder inputs. So basically if the input is there use it, if not ignore it. Although some inputs are must haves, O2 ,EGR , MAF and such. Could be wrong , but that is how it was explained to me.

 

Funny thing is that Passlock is not paired with the key on a 2001. Sensor internal in ignition switch pairs with BCM and if OK (including serial number match between BCM and PCM) a signal is then sent to the PCM that allows the vehicle to start. So even if you think you have bypassed Passlock with a resistor or something, unless you have matching serial numbers in BCM/PCM programming its not going to start.

Yes the basic computer hardware is the same for all 0411 PCMs. However they will not work for another application without extensive programming. Its just not that simple. You cant play musical PCMs and that sounds like what might be your problem.

My final advice is to make sure the proper PCM with correct proramming for your vehicle is installed. You can buy used on Internet with proper programming already flashed to your serial number. Then clear all codes including history codes and forget about them. Then deal with whatever pops up, if any.

Good luck and best wishes on a successful repair. Over and out.