- Symptom Diagnostic Tests

1. Connect a Scan Tool to the Data Link Connector (DLC). 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 the same approximate speed, check for correct tire size, ECM MEM-CAL and Vehicle Speed Sensor.
^ If the Scan Tool and Speedometer do not display the same approximate speed, replace or exchange the Instrument Cluster refer Instrument panel, Gages And Warning Indicator. Instrument Panel, Gauges and Warning Indicators

ALTERNATE TEST
^ If the Kent Moore Tool J 38522 is available, do the following test.
2. Connect a Scan Tool to the DLC connector. Disconnect the Vehicle Speed Sensor connector. Connect a lead between the J 38522 vehicle speed generators red output terminal and the Vehicle Speed Sensor connector terminal A (LT BLU). Connect a lead between the J 38522 generator's black output and terminal B (DK GRN/YEL). 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 to the vehicle speed shown on the Scan Tool.
^ If both the Speedometer and Scan Tool display the same approximate speed, check for correct tire size, ECM MEM-CAL and Vehicle Speed Sensor.
^ If the Scan Tool and Speedometer do not display the same approximate speed, replace or exchange the Instrument Cluster. Refer Instrument Panel, Gages And Warning Indicator. Instrument Panel, Gauges and Warning Indicators