We finally had a big enough snow this year to bring the people with 4WD problems out. This one was a 2008 Chevy Silverado 2500 HD. It was from a tire distributor that has a number of these particular trucks. Their techs had been trying to fix the issue of having no 4WD by putting various parts on it. This was a Magna transfer case with RPO NQF.
They said that they had replaced the transfer case motor and buttons. I started out with the usual road test, scan, and lift check to verify the problem. Sure enough, there was no 4WD, and the TCCM had every code possible stored. I thought I'd clear the codes and start out fresh.
C0569 came back immediately: system configuration error - calibration not learned. This was a new one for me. The next step was to get authorization to do electrical diagnostics, which they agreed to. I thought, maybe they had put a transfer case control module on it, and it needed to be programmed. There were a lot of updates to it, so I reprogrammed the TCCM to the latest software, but that didn't fix it.
In the post flash note, it said that the ATC motor had to be relearned. That was a big clue. I first needed to know if the problem was mechanical or electrical, so I pulled the encoder motor and shifted it into 4WD manually. What I found was that the shaft going into the transfer case was just spinning in circles. That was a problem. I hadn't worked on one of these Magna transfer cases before. I could see why it had a learn procedure; there is no blind spline to make it go on just one way.
It has to learn where the shift rail is. There was no sign of a leak, but I pulled the plug and about a cup of oil came out.
I needed a transfer case to make this one work, so we got a remanufactured transfer case, put it all back together, and it was time to do the relearn. You have to make sure that there are no codes in the transfer case module or the relearn won't work. When the relearn was happening I could hear the motor going forward and back. The relearn was done.
The 4WD light went off and down the road it went.