Cherokee 4WD L6-4.0L VIN S (1998)
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 values are based on distance pulse messages received from the Powertrain Control
Module (PCM) on the Chrysler Collision Detection (CCD) data bus.
The PCM uses an input from the Vehicle Speed Sensor (VSS) and internal programming to decide what distance pulse signal is required. The
PCM then sends the proper message to the instrument cluster circuitry on the CCD data bus. The instrument cluster stores both the odometer and
trip odometer distance information and displays the proper value based upon ignition key-on and trip odometer reset knob inputs. The instrument
cluster also stores the odometer display mode (odometer or trip odometer), and will return to the mode that was selected prior to the ignition
switch being turned off.
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. If the
instrument cluster is receiving CCD messages, but cannot display odometer values due to an internal error, the odometer display will be blank.
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. Refer to Powertrain Management/Computer and Control systems for more information on
the PCM and the VSS. Refer to Transmission and Drivetrain for more information on the speedometer pinion gear.
The odometer and trip odometer can also be used to digitally display a stored DTC. Refer to Powertrain Management/Computer and Control
systems for more information on DTCs and their retrieval.