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). The VFD is soldered onto the cluster electronic circuit board and is visible through a window with a smoked clear lens located in the lower edge of the speedometer dial face in the instrument cluster. The dark lens over the VFD prevents it from being clearly visible when it is not illuminated. However, the odometer and trip odometer information are not displayed simultaneously The trip odometer reset switch on the instrument cluster 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, just right of the speedometer.
All odometer and trip odometer distance information is stored in the instrument cluster memory. This information can be increased when the proper inputs are provided to the instrument cluster, but the information cannot be decreased. The odometer can display values up to 999,999 kilometers (999,999 miles). The odometer latches at these values, and will not roll over to zero. 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), while 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 instrument cluster odometer/trip odometer is selected at the time that it 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 VFD is illuminated at full brightness for clear visibility. At night (exterior lamps are On) the VFD lighting level is adjusted with the other cluster illumination lamps using the panel lamps dimmer control ring on the control stalk of the left multi-function switch. The instrument cluster converts an electronic dimming level message received from the Body Control Module (BCM) over the Programmable Communication Interface (PCI) data bus to a digital dimming level signal for controlling the lighting level of the VFD. Flow- ever, a "Parade" mode position of the panel lamps dimmer control ring 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 indicator is controlled by the instrument cluster 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 last previously selected odometer or trip odometer information when the ignition switch is turned to the On or Start positions. 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 VFD illuminated will toggle the display between the odometer and trip odometer information. Each time the VFD is illuminated with the ignition switch in the On or Start positions, the display will automatically return to the last mode selected (odometer or trip odometer).
- Trip Odometer Rese - When the trip odometer reset switch button is pressed and held for longer than about two seconds with the ignition switch in the On or Start positions, the trip odometer will be reset to 0.0 kilometers miles). The VFD must be displaying the 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 each of the VFD segments 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 DRBIII scan tool is required. Refer to the appropriate diagnostic information.