1981 Corvette: Service Bulletin: Vehicle Speed Sensor Servicing

Subject: Vehicle Speed Sensor Servicing
Model and Year: 1981 Corvettes
Source: Chevrolet Dealer Service Information Bulletin
Bulletin Number: 81-I-17
Section: VIt
Date: January, 1981

TO: ALL CHEVROLET DEALERS

Beginning with the 1980 1/2 model year pull-ahead program, the speedometers of the car lines listed in the chart below [Corvette included - CAC Staff] will be equipped with an optical vehicle speed sensor (VSS). The VSS will furnish data to the ECM for activating the torque converter clutch and for influencing the Computer Command Control idle speed control system.

To diagnose and service this VSS speedometer system, code 24 of the Computer Command Control should be performed as follows:

With ignition on, engine off, probe pin #16 of the ECM with a voltmeter. Raise one wheel and rotate to observe for varying voltage.
If no variation is observed, the connection between the IP harness and VSS buffer amplifier must be disconnected. Then pin to pin voltage checks can be made of the IP harness connector to determine any problems with the IP harness.
If OK, check VSS connector.
If OK, replace VSS assembly.
If condition persists, the speedometer must be returned to an AC-Delco account authorized to repair speedometers equipped with VSS. To insure proper speedometer repair specify in the "nature of Problem" area on AC-Delco warranty claim form ACD-1078 "Code 24 VSS Problem."