Powertrain Controls - ECM/PCM

DTC 24 Vehicle Speed Sensor:

Vehicle Speed Sensor Wiring Diagram:

Circuit Description:

Vehicle speed information is provided to the Engine Control Module (ECM) by the Vehicle Speed Sensor (VSS), which is a Permanent Magnet (PM) generator mounted in the transaxle. The PM generator produces a pulsing voltage whenever vehicle speed is over about 3 mph. The AC 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. The vehicle speed can be displayed with a scan tool.

The ECM supplies a signal, on CKT 817, to operate the speedometer and the odometer. The VSS signal is also sent to the cruise control module.

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 24 will set if vehicle speed equals 0 mph when:

^ Engine speed is between about 2200 and 4400 RPM.
^ TP sensor voltage less than 2%.
^ Low load condition (low MAP voltage), high manifold vacuum).
^ Transaxle not in park or neutral.
^ VSS less than or equal to 3 mph.
^ All above conditions are met for 4 seconds.

These conditions are met during a road load deceleration.
Disregard a DTC 24 that sets when the drive wheels are not turning. This can be caused by a faulty PNP switch circuit.
The PM generator only produces a signal if the drive wheels are turning greater than 3 mph.

2. At this point, the ECM is not sending vehicle speed data to the scan tool. If the scan tool is connected and functioning properly, the ECM is at fault. If the ECM is faulty and must be replaced, the new ECM must be programmed. Refer to "ECM Replacement and Programming Procedures"

Diagnostic Aids:


Scan tool should indicate a vehicle speed whenever the drive wheels are turning greater than 3 mph.

A problem in CKT 817 will not affect the VSS input or the readings on a scan tool.

Check CKTs 400 and 401 for proper connections to be sure they are clean and tight and the harness is routed correctly. - Intermittent Malfunctions

A faulty or misadjusted Park/Neutral Position (PNP) switch can result in a false DTC 24. Use a scan tool and check for the proper signal while in a drive range. Refer to Chart C-1A Park/Neutral Switch Diagnosis for the PNP switch check.