Test 7: Speedometer Inaccurate/Inoperative
- If instrument cluster diagnostic system check has been performed, go to next step. If instrument cluster diagnostic system check has not been performed, perform instrument cluster diagnostic system check. See INSTRUMENT PANEL CLUSTER DIAGNOSTIC SYSTEM CHECK
under SELF-DIAGNOSTIC SYSTEM.
- Raise and support vehicle so wheels are off the ground. Using scan tool, select POWERTRAIN, ENGINE DATA, then DATA. Start engine. Put shift selector in gear and increase engine speed. Compare scan tool reading with speed displayed on speedometer. If scan tool reading agrees with speedometer, check for poor connections and intermittent conditions. If scan tool reading does not agree with speedometer, go to next step.
- Using a DVOM connected to ground, backprobe terminal B3 (Dark Green wire) at instrument cluster harness connector. See Figure
. Using DVOM, select AC voltage, then frequency. With vehicle speed at 20 MPH, frequency should be 18-25 Hz. If frequency is as specified, go to next step. If frequency is not as specified, go to step 5
.
- Replace instrument cluster. See INSTRUMENT CLUSTER
under REMOVAL & INSTALLATION. After repairs, go to next step.
- Check for an open, short to ground or short to power in Dark Green wire between terminal B3 at instrument cluster harness connector and terminal No. 4 at Vehicle Control Module (VCM) C4 harness connector. See Figure
and Fig 1
. Repair wiring as necessary and go to next step.
- Connect all disconnected components. Check system for proper operation. If system operates properly, test is complete. If system does not operate properly, go to step 2
.
Courtesy of GENERAL MOTORS CORP.