Grand Cherokee 2WD L6-4.0L VIN S (1997)
Odometer: Description and Operation
SYSTEM OPERATION
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 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 the distance values that are received from the Body Control Module (BCM) on the
Chrysler Collision Detection (CCD) data bus.
The BCM uses an input from the Powertrain Control Module (PCM) and internal programming to calculate the distance value. The PCM uses an
input from the Vehicle Speed Sensor (VSS) to send a distance pulse signal 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.
