Electronic Speedometer

The instrument cluster contains a high-torque type electric speedometer. Integrated circuits control the air core speedometer and the stepper motor odometer. A removable bulb and socket assembly, that inserts into the back of the instrument cluster, provides the lighting of the speedometer.

The speedometer system consists of the following components:
^ The instrument cluster
^ The Vehicle Speed Sensor (VSS)
^ The Vehicle Control Module (VCM)
^ The Powertrain Control Module (PCM) (Diesel only)
^ Any related wiring

The 1 piece instrument cluster mounts in front of the driver in the instrument panel. The instrument cluster is not serviceable. If a diagnosis leads to a malfunctioning instrument cluster, you must repair or replace the instrument cluster through an authorized service center.

Diesel applications use a VSS buffer in the speedometer system. The VSS buffer is a solid-state device that converts the analog output from the VSS to a digital signal that contains 4,000 pulses per mile for the instrument cluster.

The VSS buffer matches to the final drive and tire size of each vehicle. Replace the VSS buffer with the proper VSS buffer part number that matches the vehicle. If the final drive or tire size changes for any reason, replace the VSS buffer with the buffer that matches the new final drive or tire size. If you do not do this, the signal will not be accurate for proper speedometer/odometer calibration. An incorrect VSS buffer may also affect the following components:
^ The antilock brakes
^ The automatic transmission
^ The Vehicle Control Module (VCM)
^ The Powertrain Control Module (PCM) (Diesel only)
^ All cruise control systems

The VSS buffer attaches to the bottom rear of the instrument panel carrier, to the right of the steering column.

The VSS is a permanent magnet signal generator that sends an analog signal proportional to the propeller shaft speed to the VCM (Gasoline engines), or to the VSS buffer (Diesel engines).

The VSS mounts to the transmission tailshaft extension housing. Refer to Vehicle Speed Sensor Replacement or Vehicle Speed Sensor Replacement in Automatic Transmission - 4L60E or Automatic Transmission - 4L80E.