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Vehicle Speed Sensor

  1. The following speed procedure applies if Code 24 is stored in ECM or suspected incorrect input from vehicle speed sensor exists. Connector C1 (10-wire connector) is located on right corner of instrument cluster and C12 (12-wire connector) is located on left side of instrument cluster.
  2. Check speedometer operation. If speedometer operates correctly, proceed to step 3). Repair or replace speedometer if speedometer is not operating properly.
  3. Disconnect C1 (right side) connector from instrument cluster. Using ohmmeter, measure resistance from Black/Blue wire of C1 connector and ground. If resistance is less than .3 ohm, proceed to step 4). If resistance is greater than .3 ohm, repair Black/Blue wire between instrument cluster and ground connection, located left of cigarette lighter and lower support on instrument panel.
  4. Disconnect C2 (left side) connector from instrument cluster. Turn ignition on. Using voltmeter, measure voltage from Yellow/Green wire of connector C2 and ground. If voltage is greater than 5 volts, proceed to step 8). If voltage is less than 5 volts, proceed to step 5).
  5. Turn ignition off. Disconnect 18-pin connector from ECM, located under left side of dash. Using ohmmeter, measure resistance between Yellow/Green wire of ECM connector and C2 (left side) instrument cluster connector.
  6. If resistance is greater than .3 ohm, repair open circuit in Yellow/Green wire. If resistance is less than .3 ohm, proceed to step 7).
  7. Connect ohmmeter form Yellow/green wire of 18-pin ECM connector and ground. If continuity exists, repair short to ground in Yellow/Green wire. If no continuity exists, replace ECM.
  8. Disconnect speedometer cable from speedometer. Connect ohmmeter across terminals No. 1 and 2 of vehicle speed sensor. See Fig 1 . Measure resistance while rotating speedometer head.
  9. 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.
Fig 1: Vehicle Speed Sensor Terminal ID
G90D17940Courtesy of GENERAL MOTORS CORP.
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