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Jerry Newton
Jerry Newton, GMC Technician
Category: GM
Satisfied Customers: 4608
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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GM Yukon Denali: 06 Yukon Denali wont shift into overdrive

Customer Question

06 Yukon Denali wont shift into overdrive
Submitted: 2 years ago.
Category: GM
Expert:  Jerry Newton replied 2 years ago.
Just 4th gear missing? It has 1, 2, and 3 for sure?
Customer: replied 2 years ago.
Yes
Customer: replied 2 years ago.
Doing over 2000 rpms at 70
Expert:  Jerry Newton replied 2 years ago.
If it's only 4th gear, that isolates it to just a couple of possibilities. First, 4th gear might be inhibited electronically by the computer. I'd want to attach a scan tool and see if that's the case, make sure the TCM is commanding 4th gear, and that there isn't a trouble code which might inhibit 4th gear operation. If the TCM is commanding 4th gear and it's just not shifting, then hydraulically the diagnosis centers around the 2-4 band. Though the band operates in 2 and 4, there are separate fluid circuits and pistons that make this occur, so I'd be wanting to look very closely at that hydraulic circuit and the hardware (piston, seal, etc.). 2000 at 70 doesn't seem that far out of range, are you sure that 4th gear isn't occurring? When driving at 70, if you move the shifter to Drive, does the tach jump up several hundred RPM or does it stay exactly the same?
Customer: replied 2 years ago.
SAme
Expert:  Jerry Newton replied 2 years ago.
OK. The diagnosis tips I gave are what I'd be doing, starting with a good quality scan tool that is capable of reading transmission data.
Customer: replied 2 years ago.
Thanks
Expert:  Jerry Newton replied 2 years ago.
You're welcome. If you need anything else, please let me know.