Vehicle Speed Sensor Check (4WD): Notes

The Vehicle Speed Sensor (VSS) circuit consists of a magnetic induction-type sensor, vehicle speed sensor buffer module, 4WD low switch and wiring. Gear teeth, pressed on outside diameter of output carrier assembly, induce an alternating current in the sensor. This current is transmitted to the buffer module. Buffer module compensates for various axle ratios, and converts signal to a square wave for use by speedometer, cruise control, anti-lock brake system and PCM.

Buffer module sends 2 different signals to PCM. Circuit No. 437 relays transfer case output speed to PCM. PCM uses transfer case output speed signal and 4WD low switch to determine transmission output shaft speed. PCM uses transmission output shaft speed to control shift points, line pressure, TCC, Code 24 and Code 72. Circuit No. 1716 relays vehicle speed, which is used to control engine operating functions and Code 16.

NOTE: Test numbers refer to numbers on diagnostic chart.

This test checks VSS signal to PCM.
This test checks VSS signal to the buffer module.
This test checks VSS signal.