DTC 24

Chart - Code 24 Vehicle Speed Sensor:

Wiring Diagram for Vehicle Speed Sensor.:

CODE 24


VEHICLE SPEED SENSOR (VSS) CIRCUIT


Circuit Description:


Vehicle speed information is provided to the ECM by the vehicle speed sensor, a permanent magnet (PM) generator mounted in the transmission. The PM generator produces a pulsing voltage whenever vehicle speed is over about 3 mph. The A/C voltage level and the number of pulses increases with vehicle speed. The ECM converts the pulsing voltage to mph, and the mph can be displayed with a "Scan" tool. The function of the VSS buffer, used in past model years, has been incorporated into the ECM. The ECM supplies the necessary signal for the instrument panel (4004 pulses per mile) for operating the speedometer and the odometer.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. Code 24 will set if vehicle speed signal equals less than 3 mph when:
Engine is running.
No Code 29 or 31.
When the vehicle is in 4th gear.
All conditions met for 40 seconds.
The PM generator only produces a signal if drive wheels are turning greater then 3 mph.

2. Before replacing the ECM, check the Mem-Cal for correct application.


Diagnostic Aids:


"Scan" should indicate a vehicle speed whenever the drive wheels are turning greater than 3 mph. Check CKT 400 and 401 for proper connections to be sure they are clean and tight and the harness is routed correctly. Refer to "Intermittents" in DIAGNOSIS BY SYMPTOM - NO TROUBLE CODE STORED.