Speedometer

The speedometer is an analog gauge that is located in the instrument cluster. The PCM/VCM receives an analog input from the vehicle speed sensor and converts it to a digital signal containing 4,000 pulses per mile (PPM) for the instrument cluster.

The PCM/VCM sends this digital output (4,000 PPM) to the instrument cluster on a designated circuit. These pulses can be measured in Hertz (Hz) using a Digital Multimeter (DMM) on the AC scale. The PCM/VCM calibration 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 antilock brakes and the cruise control systems.

The speedometer system consists of the instrument cluster, Vehicle Speed Sensor (VSS), PCM/VCM and related wiring. 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 (2WD) models and the transfer case output shaft housing on 4-Wheel Drive (4WD) models.

Repairs to the instrument cluster can only be performed by an authorized instrument cluster service center.