Fan clutch, APPS, Possible harness issues? SES and REP lights

[AV8ER]

This will be the second time this has happened in the past few months. While I am sitting still the REP light comes on as well as the car throwing more codes. Ive had a P0526 and i believe a P0480 code for awhile now but has never caused me any problems other than having the SES light on constantly. When the REP light comes on it puts out a P0641, P2138, P0000, P0000 as well as the P0526 but the P0480 is gone. After turning the key off and back on the REP light goes off and I am able to drive away with no problem. I found a few threads taliking about one or more of these problems individually but not all of them. I know the 0641 is a 5v reference voltage problem, 2138 is accelerator pedal position sensor problem, 0000 is a generic problem i think, 0526 is fan speed sensor circuit, and the 0480 is another related to the fan clutch. Any ideas on want to check and where to start would be appreciated. Or any direction to another thread with answers would be nice. Thanks

 

[The_Roadie]

The 5V reference voltage comes out of the PCM, and then goes to FIVE separate things - the fan clutch RPM sensor, the two accel pedal sensors, and the two throttle body position sensors. A problem with the wiring or any of those five sensors could cause an REP and many SES codes. Difficult to tell which one it is without shotgunning, but you can easily disconnect the fan clutch harness and drive around for a while. Got a voltmeter to look at the 5V reference signal and watch for perturbations?

 

[AV8ER]

I do have a dmm

 

[The_Roadie]

So start monitoring the 5V reference all the time. Install extension wires to the accel pedal harness to have access where your meter can be seen. I have a dozen little tap wires various places in case I need them (again).

 

[AV8ER]

Will do thanks! The p0526 has been on for some time now (about a year) is there a normal cause for that

 

[AV8ER]

I forgot this too. When the code originally appeared it happened when my fan shroud came in contact with the fan. Come to find out when the clutch was replaced last the bottom clips of the shroud did not get hooked properly

 

[ace]

Having the same issues here, disconnected the fan clutch harness and drove around, same issues, going to pull the throttle body and clean it as I have not cleaned it in over 60k. Wondering if it could actually be the APPS. The Fan clutch seems to function properly when tested, and unplugged I can't seem to drive more than 5 miles without REP coming on with same codes. With each test I'm clearing codes. Wondering what else I can check before buying parts. Visual inspection of fan harness looks clean and still wrapped in the loom I put on it when I installed the fan a couple years ago. Hoping that you may have something more to check before I replace the APPS.

Didn't want to start a new thread.

Code P1271
GMC Envoy XL
4.2 4wd

 

[The_Roadie]

Check the voltages at the pedal sensor connector to see if the 5V reference and ground get there, and that the two sensor outputs move smoothly and in the opposite directions when you press on the pedal.