ATSG CONFIRMED FIX - MARCH 2023
2009 GMC Sierra 2500 6L90
Complaint: Transmission is taking off in 2nd gear and is being commanded to take off in 2nd gear.
Cause: The wire as chaffed in the harness next to the alternator mounting bracket.
Correction: Repair the wire in the harness and the insulating tubing around the harness as well as secure the harness to prevent further damage.
Part numbers related to the repair: N/A
Year Make and Model of the Vehicle: 2009 GMC Sierra 2500
Mileage: NA
Shop Name: Mr. Transmission
Transmission: 6L90E
Additional Notes: EMI was getting induced into the electrical system. Most likely the TCM may be confusing this with output speed, however the scanner was not showing any OSS signal during diagnosis. Check the attached photos of harness damage.
Pictures/Diagram: Included below
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