Code 24 Vehicle Speed Sensor (VSS) Circuit: Notes

ECM supplies 12 volts to VSS. With vehicle moving, reed switch inside VSS will open and close 4 times per revolution of speedometer cable. As reed switch opens and closes, voltage at ECM is toggled high and low. ECM converts this toggled voltage into vehicle speed displayed as MPH or KPH. Code 24 will set if constant voltage (high or low) lasts at least 4 seconds.

1. Checks for intermittents.
2. Checks for VSS not receiving 12 volts from ECM (open in Yellow/Green wire or faulty ECM).
3. Checks for poor ground connection or a faulty VSS.