Speedometer Is Inoperative Or Inaccurate

1. Disconnect Vehicle Speed Sensor (VSS) from top of transaxle. Connect Instrument Panel Tester (J 33431-B) to VSS connector. Set tester to 54 MPH. Turn ignition on. If speedometer reads 6 MPH, check for poor connection at VSS. If connection is okay, replace VSS. If speedometer does not reads 6 MPH, go to next step.
2. Turn ignition off. Remove tester from VSS. Disconnect VSS buffer located behind instrument panel, above convenience center. See Fig 1 . Connect Instrument Panel Tester (J 33431-B) to terminal "F" (Dark Green wire) of VSS buffer connector C1.
3. Set tester to 54 MPH. Turn ignition on. If speedometer reads 54 MPH, check for poor connection at VSS buffer. If connection is okay, replace VSS buffer. If speedometer does not read 54 MPH, check for open or short circuit in Dark Green wire. If wire is okay, replace speedometer.

Fig 1: Locating VSS Buffer

Courtesy of GENERAL MOTORS CORP.