2002 Yukon XL Won't Shift into 4HI or HLO

Asked by Dec 02, 2018 at 12:29 AM about the 2002 GMC Yukon XL 1500 SLT

Question type: Maintenance & Repair

My 2002 Yukon is stuck in 2HI and the cab switch just blinks when I try to
switch into 4Hi, 4Lo, or Auto. I don't get the clunk. I've already replaced the
front actuator as well as the switch in the cab. I am getting 12V to the
actuator although I can't say for sure that it's engaging. The 4WD fuse also
tested fine.

I have now turned my attention to the transfer case motor. I am getting 5
volts to the green and brown/white going to the motor and the ground seems
to be find as well. I tried to backprobe the brown/white wire so I could test for
a voltage difference when I switch into 4Hi or 4Lo. What happens however is
that my backprobe reads 5 Volt when the connector is unplugged from the
motor but when I attached the wiring harness to the motor and test voltage
(grounding to the battery) I can zero. I have no idea what this means, might
there be a short in the motor?

I appreciate any insights!!

6 Answers

258,955

Maybe the transfer case is the problem.

2 people found this helpful.
197,735

That's signal voltage from the GEM so it knows what position the shift motor is in, 4HI, 4LO, 2WD or AUTO. Transfercase shift motors are a common failure on just about everyone that uses electronic shifting. Sometimes you can get the motor to run if you tap it with a small hammer (or rock it stuck off road) while someone hold the 4HI button and it might run a time or two, I had to replace that motor on both a Ford Bronco and a Chevy Tahoe that I have owned.

1 people found this helpful.

Thank you, I'll get under it again and see if tapping changes things.

I tried tapping the shift motor and it didn't change anything. Before I replaced the shift motor I shifted it to N successfully which was a good sign? Regardless, I replaced the motor and seemed to successfully shift into 4HI once afterwords, but pretty quickly something happened and the Service 4WD light came on. Now I don't even get an indicator light on the button panel. I am guessing I have a more serious problem?

197,735

You might want to check the harness right where it comes out of the floor, I have seen a few rigs that have had to much wire flex and caused intermittent connection problem or a bad ground supply, if it's not there then you should take it to a shop you trust, tell them what you have done so far. Who knows it could just be a bad relay.

Thank you tennisshoes. I replaced all the brake lines a few months ago and it's possible I disturbed the wiring harness. I'll take a look.

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