- Symptom Diagnostic Tests

Connect a bi-directional scan tool to the Assembly Line Diagnostic Link (ALDL) connector. Drive the vehicle or simulate vehicle speed using J38522 vehicle speed signal generator. Observe the Speedometer and/or Head Up Display (if equipped) and compare it to the vehicle speed shown on the scan tool.

^ If both the Speedometer and scan tool display the same speed, check for correct tire size and inflation, PCM MEM CAL, and Vehicle Speed Sensor.
^ If the scan tool and Speedometer do not display the same speed, replace the Instrument Cluster.