Transfer Case Encoder Replacement

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pincusa

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Jun 26, 2008
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A few months ago, my 03 Tahoe started giving me the 'Service 4WD' errors. Restart, and they went away, but I knew I had to address them at some point. The dealer wanted $85 to pull the codes, and wouldn't budge from it (no wonder GM is in trouble!) I got a guy to pull the codes, but he only gave me the errors, not the error codes.

I purchased a replacement encoder PN 88962315 for my NP8 transfer case assuming that was the cause of the issues (big assumption I know, but w/o the real codes I didn't know where to start)

I found this thread on how to get to the motor. A great link, but I didn't want to replace the whole motor. I wanted to just do the encoder inside.
http://www.tahoeforum.com/showthread.php?p=112227

I managed to get out of the GM dealer this print out which outlines the replacement. It also had the needed part numbers

In the end, it was an easy change. Be sure to keep the orientation and mark things with a sharpe! I can’t stress enough how much time could be wasted if you lost the orientation of the unit! While I put my truck in neutral before I started, and the neutral light did come on the dash, when I took the motor apart, the marks weren't lined up so it wasn't really in neutral (which would also explain why I couldn't roll the truck even though the red neutral light was on).

The encoder is a slightly different unit then the one I took out. It looks like GM MIGHT have redesigned it to prevent it from failing in the future. Time will tell. If I get time, I'll try to connect a ohm meter to the bad unit to see if there are dead spots in it (I'm guessing that's the cause of the problem)

In the end, it was an easy job and saved me a few hundred $ in buying a whole motor unit. I estimate it took me about 1.5 hrs with the oil change. I also changed the transfer case oil while I was there. Most of that was spent fighting with the clamp on the front axle boot.

The noise that would come out of the drivetrain when it was in Auto is gone (I'm guessing it's not fully engaged or the oil changed helped that?). The unit now changes as it should, and I hope this will prevent future errors. I might still go back for a firmware update... We'll see.

Hope this helps someone else!

View attachment scan.zip
 
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