Speedometer Head: Testing and Inspection

SPEEDOMETER IS INACCURATE (TEST A)

1. 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 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 Panel.


ALTERNATE TEST

- If the Kent Moore Tool J38522 is available, do the following test.

2. Connect a Scan Tool to the ALDL connector. Disconnect the Vehicle Speed Sensor connector. Connect a lead between the J38522 vehicle speed generator's red output terminal and the Vehicle Speed Sensor connector terminal A (YEL). Connect a lead between the J38522 generator's black output 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 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.

SPEEDOMETER/ODOMETER DON'T WORK (TEST B)