Odometer and Trip Odometer

The odometer and the trip odometer share the same Liquid Crystal Display (LCD) on 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 upon odometer and trip odometer messages received from the Powertrain Control Module (PCM) on the Chrysler Collision Detection (CCD) data bus.

The PCM uses a speed pulse input received from the Controller Anti-lock Brake (CAB) and internal programming to decide what vehicle speed and distance messages are required. The PCM then sends the proper messages to the instrument cluster circuitry on the CCD data bus. The CAB uses an input from the rear wheel speed sensor and internal programming, which includes a programmable pinion factor to compensate for different axle gear ratios and tire sizes, to determine what speed pulse output is required. The CAB then sends the proper speed pulse to the PCM on a hard wired circuit.

The instrument cluster stores both the last odometer and last trip odometer distance messages it receives from the PCM, and displays the proper value based upon ignition key-on and trip odometer reset knob inputs. If the instrument cluster stops receiving distance messages from the PCM during its current ignition key-on cycle, the odometer or trip odometer will display the last distance value that was received. If the instrument cluster has not received any distance messages from the PCM during its current ignition key-on cycle, the odometer or trip odometer display will blink.

The rear wheel speed sensor is excited by an exciter ring on the differential case within the rear axle housing. Incorrect tire size, incorrect axle ratio, an incorrect pinion factor, a faulty or improperly installed rear wheel speed sensor, a faulty rear axle exciter ring, or a faulty CAB can each result in inaccurate odometer readings. For diagnosis of the odometer and trip odometer inputs, a DRB scan tool and the proper Diagnostic Procedures are recommended.