Auto/4Hi Won’t Engage

DeathRowe015 · January 27, 2020

2015 GMC Sierra with 64000 miles on the truck and have used the 4Hi a handful of times. Went to use it the other day and the lights on the switch would blink and then turn off (not constant on like it should) and not engage. Same for the auto mode. Got to playing around with it today and the only way I can get the Auto or 4Hi to engage is to first engage the 4Lo. Once in 4Lo I can cycle to 4Hi and auto and 2wd no problem. But after running in 2wd for a few miles. Same thing, cannot switch to auto or 4Hi until I switch to 4Lo first.

Anyone experience this or have similar issues? Or suggestions on source of the problem?

Thanks!

Update: Issue was fixed by re-coding the transfer case module. There is apparently a bulletin out for this issue.

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JimCost2014 · January 27, 2020

1 hour ago, DeathRowe015 said:

2015 GMC Sierra with 64000 miles on the truck and have used the 4Hi a handful of times. Went to use it the other day and the lights on the switch would blink and then turn off (not constant on like it should) and not engage. Same for the auto mode. Got to playing around with it today and the only way I can get the Auto or 4Hi to engage is to first engage the 4Lo. Once in 4Lo I can cycle to 4Hi and auto and 2wd no problem. But after running in 2wd for a few miles. Same thing, cannot switch to auto or 4Hi until I switch to 4Lo first.

Anyone experience this or have similar issues? Or suggestions on source of the problem?

Thanks!

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Do have the ability to check for codes, should be something there if it is not working.

List of things that could be wrong are, bad switch, bad ground, case itself is damaged, bad pump, bad actuator, I would start with finding a code, this has been a common problem in the last 3 body styles.

tlaw91 · February 2, 2020

Had done like this beat me up for a minute!

You may have an issue with water intrusion into your front axle actuator

Hope this helps

-Friendly neighborhood GM tech guessing

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DeathRowe015 · February 2, 2020

Well I got it solved for now. Apparently there is a bulletin out for this issue. I got talking to the service desk when taking the truck in for the increased brake pedal effort recall. They did some digging and basically re coded the transfer case module and it is working for now.

Thanks for all the suggestions!

Hopefully it stays fixed.

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tlaw91 · February 2, 2020

Yeah I did that to the one I had and didn’t fix it, ended up being the motor for the front axle. Glad a program fixed yours!!

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