Engine Diagnosis

Diagnostic Trouble Code 24:

Vehicle Speed Sensor Circuit:

CIRCUIT DESCRIPTION
The Vehicle Speed Sensor (VSS) circuit consists of a magnetic induction type sensor, VSS buffer and wiring. Gear teeth pressed on the outside diameter of the output carrier assembly induce an alternating current in the sensor. On two wheel drive vehicles, this current is transmitted to the vehicle speed signal buffer where it is passed on to the PCM. The VSS buffer compensates for various axle ratios and converts the signal to a square wave for use by the speedometer, cruise control and antilock brake system. Since vehicle speed is taken from the transfer case on four wheel drive vehicles, the transmission vehicle speed sensor signal on these units goes directly to the PCM. DTC 24 will set when vehicle speed is more than 7 mph for over 10 seconds while vehicle speed buffer pulses equal zero.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Verifies power and ground to VSS buffer module.

2. The first test checks the vehicle speed sensor signal to the PCM.

3. Test two checks the vehicle speed sensor signal to the digital ratio adapter.

4. Test three directly verifies the vehicle speed sensor signal.

DIAGNOSTIC AIDS
Check all connections especially at the transmission pass-thru connector.

Refer to Diagnosis By Symptom / Intermittents - Intermittent Malfunctions