Code 24: VSS: Notes

WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 1990 Pontiac Grand Am, 1990 Pontiac 6000, 1990 Oldsmobile Cutlass Cruiser, 1990 Oldsmobile Cutlass Ciera, and 1990 Oldsmobile Cutlass Calais. However, it is still accessible from the selected car via links, so may be relevant.

The speed sensor, which is a Permanent Magnet (PM) generator, provides the ECM with vehicle speed information. The PM generator, mounted in the transmission, produces a pulsing voltage signal whenever the vehicle speed is more than 3 MPH. The voltage level and pulses increase with vehicle speed. The ECM converts the pulsing voltage to MPH, which is used by the ECM in calculations to determine vehicle adjustments.

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

A Code 24 will set when MPH reads zero, transmission is not in Park or Neutral, engine speed is between 1800-4400 RPM, TPS is at zero percent (closed throttle) and a high manifold vacuum is sensed by the MAP sensor. All of these conditions must be met for 3-5 seconds. The PM generator only produces a voltage signal if drive wheels are turning greater than 3 MPH.
Before replacing the ECM, PROM should be checked for correct application.