Grand Cherokee 2WD V8-5.2L VIN Y (1998)
Odometer: Description and Operation
SYSTEM OPERATION
Odometer and Trip Odometer
The odometer and the trip odometer share the same vacuum fluorescent digital display tube in the instrument cluster circuit board. Each gives an
indication of the distance the vehicle has travelled. However, by depressing the reset knob on the face of the instrument cluster, the display mode
can be switched from odometer to trip odometer. Depressing the reset knob for longer than two seconds while in the trip odometer mode will reset
the trip odometer to zero. The odometer and trip odometer display values are based on distance messages received from the Body Control Module
(BCM) on the Chrysler Collision Detection (CCD) data bus.
The BCM uses a distance pulse message relayed from the Powertrain Control Module (PCM) on the CCD data bus and internal programming to
decide what distance message is required. The PCM receives the distance pulse signal input from the Vehicle Speed Sensor (VSS) to relay to the
BCM on the CCD data bus. The BCM stores both the odometer and trip odometer distance information and sends the proper value to the
instrument cluster based upon ignition key-on and trip odometer reset knob messages received on the CCD data bus.
If the instrument cluster is not receiving distance information on the CCD data bus when the ignition switch is turned to the On position, the
odometer display will remain blank. If the instrument cluster does not receive a distance message on the CCD data bus after the ignition switch has
been turned to the On position, the instrument panel circuitry will insert the last normally displayed distance in the odometer display
The VSS is a hall-effect sensor that is installed in the transmission (two-wheel drive) or transfer case (four-wheel drive), and is driven by the
output shaft through a speedometer pinion gear. Incorrect tire size, incorrect axle ratio, a faulty or incorrect speedometer pinion gear, or a faulty
VSS can each result in inaccurate odometer readings.
