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1999 transfer case short.


Ghostdragon
10-09-2022, 07:50 AM
I have a 1999 Suburban with the NP246 RPO NP8 4 button switch auto 4x4. Problem: Transfercase Fuse 2(20A) has a direct short, 12v drop.

Wondering if someone can suggest the next troubleshooting steps. This is my diagnostic process so far.

The switch lights were acting funny prior to losing four-wheel drive, so when it went out, I suspected the switch. Was at junkyard so I grabbed one and installed it. The lights lit up but still no 4wheel drive. I believe when turn ignition to run position, the lights are supposed to light up, then blink to current gear selection. Been a couple weeks ago so I forget exactly what it did, but I think a couple lights stayed on.
So next I checked the transfer case fuse and it was blown. So I pulled the plugs on encoder motor and axle actuator. Still has 12v drop at fuse. pulled the tccm and only when unplugged connector C1(32 pin orange plug) did the short go away. I thought maybe internally shorted so I got one off ebay. plugged new tccm in, and still have a 12v drop at fuse. Next decided to check all the sockets in connecter C1 for chassis ground. Only socket E15(module grd) showed continuity with chassis ground. So thought possible that new tccm may be shorted also, so tested all pins for continuity to module ground. The only pins that were grounded were front and rear shaft speed sensor returns(E13,F6), and Encoder return(F12). I believe those to be ground.
Well thats as far as my diagnostic skills go, im at a dead end. Today I think ill go out and visually inspect all the wires undercarriage and disconnect everything again, this time sensors too. Thanks for any ideas you may have.

j cAT
10-15-2022, 12:10 PM
I use the actron CP9680 .... GM do all the codes ..eng/drive train/abs/air bags ..

now you have to scan the vehicle .... then post on the forums..

some people the harness is the falling off..............from the fuse box hood to the tranfercase ... then the wire is worn and grounded .. blown the fuse ...

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