Code 24: VSS: Notes

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.

1. A Code 24 will set when MPH reads zero, transmission is not in Park or Neutral, engine speed is between 1200-4400 RPM, TPS is less than 2 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.
2. If 8-12 volts are present at the instrument panel (I/P) connector, there is an open between I/P connector and VSS or a faulty vehicle speed sensor. A voltage signal of less than one volt at the I/P connector indicates signal line is shorted to ground or open. If line is not open or grounded, check for faulty ECM connections or faulty ECM.