Code 24 - Output Speed Sensor Low (1992 2WD): Notes

Fig 1: Output Speed Sensor Component Diagram (1992 2WD)

Courtesy of GENERAL MOTORS CORP.

The speed sensor, which is a Permanent Magnet (PM) generator, provides Digital Ratio Adapter Control (DRAC) with vehicle speed information. PM generator, mounted in transmission, produces a pulsing voltage signal whenever vehicle speed is more than 3 MPH. Voltage level and pulse increase with vehicle speed. DRAC converts PM generator signal to a pulsing signal by grounding circuit 437 (Brown wire) 2000 times per mile. Control module uses this signal in calculations to determine vehicle adjustments.

Code 24 will set under following conditions: vehicle speed is zero, transmission is not in Park or Neutral, engine speed is more than 3000 RPM, and PCM/TCM input circuit 437 is constant. All of these conditions must be met for 1.5 seconds. PM generator only produces voltage signal if drive wheels are turning faster than 3 MPH.

1. This tests for voltage variation while wheels are turning. Voltage will be low at low wheel speeds (4-6 volts at 20 MPH).
2. This step determines whether VSS assembly is faulty, circuit 437 is grounded, or PCM/TCM connector or PCM/TCM is faulty.
3. This signal indicates an open circuit 437 or faulty DRAC.
4. This is a normal voltage signal.