Code 24: Vehicle Speed Sensor (VSS) (L Body): Notes
Vehicle speed information is provided to the ECM by the vehicle speed sensor, which is a permanent magnet (PM) generator. It is mounted in the transaxle. The PM generator produces a pulsing voltage whenever vehicle speed is over 3 mph. The A/C voltage level and the number of pulses increases with vehicle speed. The ECM then converts the pulsing voltage to MPH, which is used for calculations, and the MPH can be displayed with the "SCAN" tester.
The function of VSS buffer used in past model years has been incorporated into the ECM. The ECM then supplies the necessary signal for the instrument panel (4000 pulses per mile) for operating the speedometer and the odometer. If the vehicle is equipped with cruise control the ECM also provides a signal (2000 pulses per mile) to the cruise control module.
- Code 24 will set if vehicle speed equals 20 mph when the following conditions occur:
- Engine speed is between 1100 and 4400 RPM.
- Low load condition, low MAP voltage, high manifold vacuum.
- Not in park or neutral.
- All conditions met for 5 seconds. These conditions are met during a road load deceleration. Disregard Code 24 that sets when drive wheels are not turning. The PM generator only produces a signal when the drive wheels are turning more than 3 mph.