STUCK IN FIRST GEAR (4L80E) (REPLACE INPUT SPEED SENSOR)

THE SERVICE INFORMATION SHOWN BELOW IS INTENDED FOR ELECTRONIC DELIVERY TO SERVICE TECHNICIANS. DUE TO THE NATURE OF THIS INFORMATION, IT IS NOT INTENDED FOR PAPER PUBLICATION.

WHEN DIAGNOSING A 1991 OR 1992 TRUCK EQUIPPED WITH A 4L80E FOR A CONDITION OF NO UPSHIFT OR STUCK IN 1ST GEAR AND NO CODES ARE STORED, CHECK FOR AN INPUT SPEED SENSOR MALFUNCTION. IF THE INPUT SPEED SENSOR IS NOT FUNCTIONING, THEN THE OUTPUT SPEED SENSOR IS NOT USED FOR REFERENCE BY THE PCM/TCM AND AN UPSHIFT CANNOT OCCUR.

DISCLAIMER

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.