Odometer: Description and Operation
ODOMETERAn odometer and trip odometer are standard equipment in all instrument clusters. The odometer and trip odometer information are displayed in a common electronic, blue-green Vacuum-Fluorescent Display (VFD), which is located in the lower edge of the speedometer dial face in the instrument cluster and, when illuminated, is visible through a small window cutout in the gauge overlay. However, the odometer and trip odometer information are not displayed simultaneously. The trip odometer reset switch on the instrument cluster electronic circuit board toggles the display between odometer and trip odometer modes by depressing the odometer/trip odometer switch button that extends through the lower edge of the cluster lens to the right of the speedometer.
All odometer and trip odometer distance information is stored in the instrument cluster memory This distance information can be increased when the proper inputs are provided to the instrument cluster, but the distance information cannot be decreased. The odometer can display values up to 999,999 kilometers (999,999 miles). The odometer will not roll over, but will latch at the maximum value. The trip odometer can display values up to 999.9 kilometers (999.9 miles) before it rolls over to zero. The odometer display does not have a decimal point and will not show values less than a full unit (kilometer or mile), the trip odometer display does have a decimal point and will show tenths of a unit (kilometer or mile).
The unit of measure for the odometer and trip odometer display is not shown in the VFD. The unit of measure for the odometer/trip odometer is selected at the time that the instrument cluster is manufactured, and cannot be changed. If the instrument cluster has a kilometers-per-hour primary speedometer scale, the odometer/trip odometer registers kilometers; and, if the cluster features a miles-per-hour primary speedometer scale, the odometer/trip odometer registers miles.
During daylight hours (exterior lamps OFF) the VFD is illuminated at full brightness for clear visibility. At night (exterior lamps are ON) the instrument cluster converts an electronic dimming level message received from the Body Control Module (BCM) over the Programmable Communications Interface (PCI) data bus to a digital dimming level signal for controlling the lighting level of the VFD. However, a "Parade" mode position of the panel lamps dimmer control ring on the control stalk of the left (lighting) multi-function switch allows the VFD to be illuminated at full brightness if the exterior lamps are turned ON during daylight hours.
The VFD, the trip odometer switch, and the trip odometer switch button are serviced as a unit with the instrument cluster.
The odometer and trip odometer give an indication to the vehicle operator of the distance the vehicle has traveled. This gauge is controlled by the instrument cluster electronic circuitry based upon cluster programming and electronic messages received by the cluster from the Powertrain Control Module (PCM) over the Programmable Communications Interface (PCI) data bus. The odometer and trip odometer information is displayed by the instrument cluster Vacuum Fluorescent Display (VFD). The VFD will only display odometer or trip odometer information after the ignition switch is turned to the ON or Start positions, and will display the information in the odometer or trip odometer mode based upon the selection that was active when the ignition switch was last turned to the OFF position. The instrument cluster circuitry controls the VFD and provides the following features:
- Odometer/Trip Odometer Display Toggling - Actuating the trip odometer reset switch button momentarily with the ignition switch in the ON position will toggle the display between the odometer and trip odometer information. Each time the ignition switch is turned to the ON or Start positions, the display will automatically return to the last mode selected (odometer or trip odometer) before the ignition switch was turned to the OFF position.
- Trip Odometer Reset - When the trip odometer reset switch button is depressed and held for longer than about two seconds with the ignitions switch in the ON or Start positions, the trip odometer will be reset to 000.0 kilometers (miles). The VFD must be displaying the current trip odometer information in order for the trip odometer information to be reset.
- Communication Error - If the cluster fails to receive a distance message during normal operation, it will hold and display the last data received until the ignition switch is turned to the OFF position. If the cluster does not receive a distance message within one second after the ignition switch is turned to the ON position, it will display the last distance message stored in the cluster memory. If it is determined that the distance information stored in the cluster memory is corrupt, it will display in the VFD. If the cluster is unable to display distance information due to an error internal to the cluster, the VFD display will be blank.
- Actuator Test - Each time the cluster is put through the actuator test, the VFD will step sequentially through a display of "000000" through "999999", then display the cluster software version number to confirm the functionality of the VFD and the cluster control circuitry.
The PCM continually monitors the vehicle speed pulse information received from the vehicle speed sensor, then sends the proper distance messages to the instrument cluster. For further diagnosis of the odometer/trip odometer or the instrument cluster circuitry that controls these functions, refer to Instrument Cluster Diagnosis and Testing. For proper diagnosis of the vehicle speed sensor, the PCM, the PCI data bus, or the electronic message inputs to the instrument cluster that control the odometer/trip odometer, a DRB III scan tool is required Refer to the appropriate diagnostic information.