4lo works but 4hi doesn't

[Chuchy]

New to the forum. Thanks in advance for the help.

I have a 2007 Yukon. When I try to shift into 4hi, the light blinks and I get a service 4wd error. I can, however, shift into 4lo. I have tried shifting into 4hi at various speeds multiple times. Any ideas of where to start? TCCM? Thanks!

 

[Chuchy]

I was really hoping there may be some ideas on this so that I could dig in on it this weekend. Thanks.

 

[mizzouguy]

Pretty sure you need to be completely stopped to shift into 4-hi and 4-lo. Maybe try reverse for a short distance?

 

[YukonandtheHOE]

Your tcase actuator is probably done, the switch indacting the TCM is probably not getting 4hi signal that it went into 4x4 so it wont put the diff in

 

[Chuchy]

Doesn't the actuator control both hi and lo. I thought I could rule that out since I had 4lo. I thought it would be more like the part sending the signal... like the TCCM?

 

[Chuchy]

Also, just for clarity, I believe you are referring to the tcase motor and not the front differential actuator, correct?

 

[Chuchy]

Nothing ??? Anyone ??

 

[cardude2000]

Wrong section.


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[YukonandtheHOE]

Also, just for clarity, I believe you are referring to the tcase motor and not the front differential actuator, correct?

Potato patato, the motor actuate's the Tcase position, so if the Dash switch requests 4hi and the Controller puts the tcase in 4hi but the normally closed switch in the Motor Actuator doesn't signal the tcm its in gear, it won't supply voltage to the diff lock actuator.