ERRATIC/NO SPEEDOMETER/TRANS OPERATION. Chevrolet Lumina 1991

Subject: ERRATIC/NO SPEEDOMETER AND ERRATIC TRANSMISSION OPERATION WITH CODE 24

ModelandYear: 1991 LUMINA WITH 4T60E AUTOMATIC TRANSMISSION AND 3.4L ENGINE

TO: ALL CHEVROLET DEALERS

BULLETIN COVERS:

A vehicle equipped with a HYDRA-MATIC 4T60-E may exhibit erratic or no speedometer reading and erratic transaxle operation. This will be accompanied by code 24. These conditions could be caused by an inoperative transaxle speed sensor. When the power- train control module (PCM) detects an inoperative speed sensor, the PCM will force the transaxle into fail-safe 3rd gear only for 3.4L twin DOHC engine equipped W cars. Fail-safe 2nd or 3rd gear operation may cause customer comments that the vehicle is sluggish or slips. Also, an intermittent speed sensor condition may result in normal operation when cold, and when the vehicle is brought up to operation temperature, erratic operation of the speedometer and transaxle.

SERVICE PROCEDURE:

Replace the transaxle speed sensor with the part listed under "SERVICE PARTS INFORMATION."

SERVICE PARTS INFORMATION:

Part Number Description Model Usage ----------- --------------------- ----------- 10456034 Speed Sensor Assembly All

Parts are currently available from GMSPO.

SERVICE MANUAL REFERENCE:

Refer to 1991 Service Manual On-Car section for proper disassembly and assembly procedures.

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.