Code 24, Vehicle Speed Sensor - C & K Series 2WD With 4L80-E Transmission: Notes

Fig 1: Code 24, VSS Circuit Diagram (C & K Series 2WD W/4L80-E Transmission)

Courtesy of GENERAL MOTORS CORP.

VSS output sensor circuit consists of a magnetic induction type speed sensor, Digital Ratio Adapter Controller (DRAC), and wiring. Gear teeth cut in the outside diameter of the rear internal gear induce an alternating current in the sensor when drive wheels are turning. Signal is transmitted to the instrument cluster DRAC where it is converted to a square wave signal which is passed on to the PCM, cruise control, speedometer, and anti-lock brake system. Code 24 will set if gear selector is not in Park or Neutral, input speed is at least 3000 RPM and output speed is less than 200 RPM for at least one second. If input speed sensor is not operational at start up, this can cause VSS to read zero.

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

Test verifies VSS voltage at PCM.
Test verifies operation of VSS.
Test checks circuits No. 821 and 822 up to the instrument cluster.