- Symptom Diagnostic Tests

Connect a Scan Tool to the ALDL Connector. Drive the vehicle; observe the Speedometer and compare it to the vehicle speed shown on the Scan Tool.

^ If both the Speedometer and Scan Tool display approximately the same speed, check for correct tire size, ECM CALPAK and Vehicle Speed Sensor.
^ If the Scan Tool and the Speedometer do not display the same speed, replace the Instrument Cluster.