Code 24, Vehicle Speed Sensor (VSS) (Pm Generator): 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 over 3 MPH. The voltage level and the number of 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.

A Code 24 will set when MPH reads zero, transmission is not in Park or Neutral, engine speed is between 1400-4400 RPM, TPS is at 2 percent (closed throttle), and a low airflow condition is sensed. All of these conditions must be met for at least 3 seconds.

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

This test monitors the ECM voltage on circuit No. 389. With wheels turning, the pulsing action created in circuits No. 400 and 401 will result in a voltage signal to the ECM and be displayed as MPH. 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.