Allison LCT1000 Buzz Noise/Feel on TCC Apply - kw accelerate engage excessive fifth GMT800 hard performance shift

The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

Some owners Chevrolet Silverado and GMC Sierra pickups equipped with the Allison LCT1000 Transmission may comment that they hear and feel a slight/light buzz type noise when TCC applies. The condition is typically noticed under light throttle conditions when the TCC applies in 5th gear. The buzz noise is audible to the ear and can typically be felt in the drivers floor pan or in the accelerator pedal and will last approximately one second.

The dealer should ensure the latest TCM calibration is installed on the 2001 models. All 2002 and future models were built with this calibration. Engineering is not working on any hardware changes to resolve this concern as the buzz is very slight and there are no durability issue associated with the buzz noise/feel. The noise is a result of the TCC being applied and the normal drop in main line pressure associated with the apply of TCC. Replacing the transmission will NOT resolve the customers concern.

.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

(01-05 Chevrolet Silverado) and (01-05 GMC Sierra)

.