Electric Speedometer

An electric speedometer drive is standard equipment on all S/T models. Integrated circuits control the air core speedometer and stepper motor odometer, Lighting is provided by removable bulb and socket assemblies that insert into the back of the instrument cluster.
The speedometer system consists of the instrument cluster, vehicle speed sensor (VSS). PCM/VCM and related wiring.
The one-piece instrument cluster mounts in front of the driver in the instrument panel. It is not serviceable. If diagnosis leads to a malfunctioning instrument cluster, it must be replaced. 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 4000 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 to match the new final drive or tire size. If not the signal will not be accurate for proper speedometer/odometer operation. Arm incorrect signal can affect antilock brakes and 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 two-wheel drive models and the transfer case output shaft housing on four-wheel drive models.