NO UPSHIFT/STUCK IN FIRST/NO CODES/EXTERIOR LEAKS

Subject: NO UPSHIFT/STUCK IN FIRST/NO CODES/EXTERIOR LEAKS

Model and Year: 1991-93 C/K, R/V, P, G TRUCKS WITH 4L80-E/4L80-EHD AUTOMATIC TRANSMISSION

Some HYDRA-MATIC 4L80-E/4L80-EHD transmissions may experience a no upshift, stuck in first with no Diagnostic Trouble Codes (DTC) stored.

CAUSE:

Input/output speed sensor malfunction, or leaking (wicking) fluid through the speed sensor connector (internal and/or external). If the input speed sensor is not functioning correctly, the output speed sensor is not used for reference by the PCM/TCM and an upshift cannot occur.

CORRECTION:

Diagnose per the input speed sensor circuit check as outlined in Section 7A of the appropriate service manual. Replace the speed sensor if necessary.

DATE OF PRODUCTION: (Figure 1) Starting January l5, 1993 (Julian Date O15) all 1993 HYDRA-MATIC 4L80-E/4L80 EHD models will have the new speed sensor assemblies.

SERVICE PARTS INFORMATION: Part # Name 8685042 Speed Sensor Assembly

Labor Codes: Replace input sensor K6311 or output sensor K6312.

Parts are expected to be available on March 22, 1993.

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.