TCC ENGAGES AT WRONG SPEED GREASE/DIRT ON SPEEDO HEAD

Vehicles exhibiting an early TCC engagement causing a stumbling or detonating condition may be due to grease or dirt on the two reflective bars of the speedometer head that serve as reflective panels for the VSS signal. Any foreign material on these bars will interfere with their reflective properties thereby generating a false vehicle speed signal.

The reflective bars should be thoroughly cleaned if this condition is found.

All other normal diagnostic procedures should be followed before suspecting this condition.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.