Code 24 - VSS: Notes

Vehicle speed information is sent to ECM from speed sensor. The speed sensor buffer functions have been incorporated into ECM. The ECM converts pulsing signal from speed sensor, about 4000 pulses per mile, to a vehicle speed. ECM then calculates vehicle speed based on the time between pulses, then sends signal to instrument cluster for speedometer and odometer operation.

NOTE: The "Scan" tester reading should closely match the speedometer reading with drive wheels turning.

NOTE: Test numbers refer to test numbers on diagnostic chart.

To avoid possible damage to CV joints on FWD vehicles, always support control arms whenever drive wheels are turning off of ground. Code 24 will set if vehicle is stopped when the following conditions occur:
- Reference signal indicates engine speed is between 1400 and 4400 RPM.
- Throttle angle is less than 2 percent (closed throttle).
- Low load condition (low airflow or high vacuum).
- Transmission not in Park or Neutral.
- All conditions met for 4-5 seconds. These conditions are met during a road load deceleration. Disregard Code 24 that sets when drive wheels are not turning.
A voltage of less than one volt at the IP connector indicates that Vehicle Speed Sensor (VSS) circuit is shorted to ground. If after disconnecting VSS, the voltage reads greater than 10 volts, the vehicle speed sensor is faulty. If voltage remains less than 10 volts, then it is possible that VSS circuit is grounded. If VSS circuit is not grounded, there is a faulty connection at the ECM, or a faulty ECM.