Symptom Related Diagnostic Procedures
PROCEDUREConnect a Scan Tool to the ALDL Connector. Disconnect the Vehicle Speed Sensor connector. Connect a lead between the J38522 Vehicle Signal Generator's red output terminal and the Vehicle Speed Sensor connector terminal A (YEL). Connect a lead between the Generator's black output terminal and the Vehicle Speed Sensor connector terminal B (PPL). Plug the Generator into the Cigar Lighter. Select 30 V P-P sine wave and set the frequency at 600 Hz. 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.