Vehicle Speed Sensor
- The following procedure applies if Code 24 is stored in ECM or suspected incorrect input from vehicle speed sensor exists.
- Check speedometer operation. If speedometer operates correctly, proceed to step 3). Repair or replace speedometer if speedometer is not operating properly.
- Disconnect 12-pin connector from instrument cluster. Using ohmmeter, measure resistance from Black/Yellow wire of connector and ground. If resistance is less than .3 ohm, proceed to step 4). If resistance is greater than .3 ohm, repair Black/Yellow wire between instrument cluster and ground connection, located behind instrument panel, above fuse block.
- Turn ignition on. Using voltmeter, measure voltage from Yellow wire of instrument cluster 12-pin connector and ground. If voltage is greater than 5 volts, proceed to step 8). If voltage is less than 5 volts, proceed to step 5).
- Turn ignition off. Disconnect 24-pin connector from ECM, located under left side of instrument panel, near kick panel. Using ohmmeter, measure resistance between Yellow wire of ECM connector and instrument cluster connector.
- If resistance is greater than .3 ohm, repair open circuit in Yellow wire. If resistance is less than .3 ohm, proceed to step 7).
- Connect ohmmeter from Yellow wire of 18-pin ECM connector and ground. If continuity exists, repair short to ground in Yellow wire. If no continuity exists, replace ECM.
- Disconnect speedometer cable from speedometer. Connect ohmmeter across vehicle speed sensor terminals at speedometer head. See Fig 1
. Measure resistance while rotating speedometer head.
- If resistance decreases to less than 5 ohms, 4 times per revolution, replace ECM. If resistance does not decrease to less than 5 ohms, 4 times per revolution, replace speedometer.
Courtesy of GENERAL MOTORS CORP.