Symptom Related Diagnostic Procedures

Enter on-board diagnostics for vehicle speed parameter number P.O.9. Drive vehicle or simulate vehicle speed using vehicle speed signal generator (GM J-38522). Observe Speedometer and compare it to vehicle speed shown on Fuel Data Center (FDC) display.
^ If both Speedometer and FDC display indicate same speed, check wiring routed to/from Vehicle Speed Sensor that may be next to ignition (spark plug) wires.
^ If FDC display and Speedometer do not display same speed, check wiring to Instrument Cluster and tires for correct size and inflation. Also check all applicable terminals at in-line connectors and at Instrument Cluster connector for proper terminal contact. Refer to TECH TIPS for inspection/repair procedures. If OK, replace the Instrument Cluster.