A/T - 4T60-E Erratic Operation/Speedometer Erratic
90Chevy35Number: 91-111-7A
Section: 7A
Date: November 1990
Corp. Bulletin No.: 077142
Subject: ERRATIC/NO SPEEDOMETER AND ERRATIC TRANSMISSION OPERATION WITH CODE 24
Model and Year: 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 powertrain 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.