The TCM is located on right front inner fender above the wheel well.
Some common signs of a bad transmission control module include:
Trouble shifting into higher gear.
Getting stuck in the same gear.
Poor fuel economy.
Check engine light comes on.
It has been found that the transmission control module (TCM) is possibly being shorted to battery voltage during vehicle diagnosis and/or repairs.
This applies to a host of GM vehicles, including the following equipped with 4T40-E or 4T45-E or 4L60-E automatic transmission:
According to GM, if the positive battery jump start post/terminal cover is removed and/or missing, and the TCM comes into contact with the positive battery jump start post/terminal during diagnosis and/or service, the TCM will be damaged and must be replaced.
Prior to removing the TCM from its mounting bracket, disconnect the negative battery cable. If service requires the negative battery cable to be installed for diagnostic purposes, unplug the TCM before it is removed from its mounting bracket. Unplugging the TCM will eliminate the possibility of damage.
NOTE: Control module damage may result when the metal case contacts battery voltage. DO NOT contact the control module metal case with battery voltage when servicing a control module, using battery booster cables or when charging the vehicle battery. DO NOT use the TCM or its mounting bracket/fasteners as the ground connection when jump starting.