Code 24 - VSS: Notes

The ECM applies and monitors 12 volts on circuit No. 437. Circuit No. 437 is connected to the vehicle speed sensor buffer in the instrument cluster. The speed sensor buffer alternately grounds circuit No. 437 when drive wheels are turning. This pulsing action takes place about 2000 times per mile and the ECM will calculate vehicle speed based on the time between pulses. "P" Bodies use a Permanent Magnet (PM) generator mounted in the transmission to send signals to the VSS buffer in the instrument panel.

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

1. 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.
2. A voltage of less than one volt at the IP connector indicates that circuit No. 437 is shorted to ground. If after disconnecting circuit No. 437 at the vehicle speed sensor, 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 circuit No. 437 wire is grounded. If circuit No. 437 is not grounded, there is a faulty connection at the ECM, or a faulty ECM.