Speedometer
The speedometer is an analog gauge in the instrument cluster. The VCM/PCM sends vehicle speed pulses to the instrument cluster on a designated circuit.
The speedometer system consists of the instrument cluster, Vehicle Speed Sensor (VSS), PCM/VCM and related wiring. Repairs to the instrument cluster can only be performed by an authorized instrument cluster service center.
The PCM/VCM converts the analog output from the vehicle speed sensor to a digital signal containing 4,000 pulses per mile (PPM) for the instrument cluster. The PCM/VCM is matched to the final drive and tire size of each vehicle. If the final drive or tire size is changed for any reason, the PCM/VCM must be updated in order to match the new final drive or tire size. If not, the signal will not be accurate for proper speedometer/odometer operation. An incorrect signal can affect the anti-lock -brakes and the cruise control systems.
The VSS is a permanent magnet signal generator that sends an analog signal proportional to the propeller shaft speed to the PCM/VCM. The VSS mounts to the transmission tailshaft extension housing on 2 wheel drive models and the transfer case output shaft housing on 4 wheel drive models.