Buzz Noise and Vibration in the Accelerator Pedal at Approx. 10 MPH on Start Up - kw 4.8 5.3 6.0 8.1 4L60E 4L65E 4L80E 4L85E accelerate Allison brakeLCT1000 condition information instrument shift

When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.

A buzz noise from the accelerator pedal area on the first acceleration after starting the vehicle can be heard and felt. This noise will occur at approximately 10 mph and will only occur the first time the vehicle reaches 10 mph after start-up. The condition will not occur again until the key is cycled off, then on. Based on the driving habits of the vehicle owner, the condition may occur at approximately the same time as the 1-2 shift of the automatic transmission.

This noise is caused by the SBA (Supplemental Brake Assist) performing a self-test. The SBA, which is mounted to the brake vacuum booster canister, is new for 2003 and provides vacuum for the brake booster in case of low vacuum or vacuum loss.

This is a normal condition, and no repair attempts should be made.

Note: The SBA (Supplemental Brake Assist ) is only on vehicles equipped with vacuum brake boosters and is not used on vehicles equipped with Hydra-Boost brake systems.

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. This diagnostic approach was developed for the vehicle with the VIN you entered and should not be automatically be used for other vehicles with similar symptoms.

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