Part 4A

FUEL GAUGE
A fuel gauge is standard equipment on all instrument clusters. The fuel gauge is located in the lower right quadrant of the instrument cluster, below the oil pressure gauge. The fuel gauge consists of a movable gauge needle or pointer controlled by the instrument cluster circuitry and a fixed 90 degree scale on the cluster overlay that reads left-to-right from E (or Empty) to F (or Full). An International Control and Display Symbol icon for "Fuel" is located on the cluster overlay, in the center of the gauge directly above the hub of the gauge needle. An arrowhead pointed to the left side of the vehicle is imprinted on the cluster overlay next to the "Fuel" icon in the fuel gauge to provide the driver with a reminder as to the location of the fuel filler access. The fuel gauge graphics are white against a black field except for a single red graduation at the low end of the gauge scale, making them clearly visible within the instrument cluster in daylight. When illuminated from behind by the panel lamps dimmer controlled cluster illumination lighting with the exterior lamps turned ON, the white graphics appear blue-green and the red graphics appear red. The orange gauge needle is internally illuminated. Gauge illumination is provided by replaceable incandescent bulb and bulb holder units located on the instrument cluster electronic circuit board. The fuel gauge is serviced as a unit with the instrument cluster.

The fuel gauge gives an indication to the vehicle operator of the level of fuel in the fuel tank. This gauge is controlled by the instrument cluster circuit board 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 fuel gauge is an air core magnetic unit that receives battery current on the instrument cluster electronic circuit board through the fused ignition switch output (run-start) circuit whenever the ignition switch is in the ON or Start positions. The cluster is programmed to move the gauge needle back to the low end of the scale after the ignition switch is turned to the OFF position. The instrument cluster circuitry controls the gauge needle position and provides the following features:

- Percent Tank Full Message - Each time the cluster receives a message from the PCM indicating the percent tank full, the cluster programming applies an algorithm to calculate the proper gauge needle position, then moves the gauge needle to the proper position on the gauge scale. The algorithm is used to dampen gauge needle movement against the negative effect that fuel sloshing within the fuel tank can have on accurate inputs from the fuel tank sending unit to the PCM.

- Less Than 12.5 Percent Tank Full Message - Each time the cluster receives messages from the PCM indicating the percent tank full is 12.5 (one- eighth) or less for 10 consecutive seconds and the vehicle speed is zero, or for 60 consecutive seconds and the vehicle speed is greater than zero, the gauge needle is moved to the proper position on the gauge scale, the low fuel indicator is illuminated, and a single chime tone is sounded. The low fuel indicator remains illuminated until the cluster receives messages from the PCM indicating that the percent tank full is greater than 12.5 (one-eighth) for 10 consecutive seconds and the vehicle speed is zero, or for 60 consecutive seconds and the vehicle speed is greater than zero, or until the ignition switch is turned to the OFF position, whichever occurs first. The chime tone feature will only repeat during the same ignition cycle if the low fuel indicator is cycled OFF and then on again by the appropriate percent tank full messages from the PCM.

- Less Than Empty Percent Tank Full Message - Each time the cluster receives a message from the PCM indicating the percent tank full is less than empty, the gauge needle is moved to the far left (low) end of the gauge scale and the low fuel indicator is illuminated immediately. This message would indicate that the fuel tank sender input to the PCM is a short circuit.

- More Than Full Percent Tank Full Message - Each time the cluster receives a message from the PCM indicating the percent tank full is more than full, the gauge needle is moved to the far left (low) end of the gauge scale and the low fuel indicator is illuminated immediately. This message would indicate that the fuel tank sender input to the PCM is an open circuit.

- Message Failure - If the cluster fails to receive a percent tank full message, it will hold the gauge needle at the last indication until a new message is received, or until the ignition switch is turned to the OFF position, whichever occurs first.

- Actuator Test - Each time the cluster is put through the actuator test, the gauge needle will be swept to several calibration points on the gauge scale in a prescribed sequence in order to confirm the functionality of the gauge and the cluster control circuitry.

The PCM continually monitors the fuel tank sending unit, then sends the proper messages to the instrument cluster. For further diagnosis of the fuel gauge or the instrument cluster circuitry that controls the gauge, (Refer to INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING).

For proper diagnosis of the fuel tank sending unit, the PCM, the PCI data bus, or the message inputs to the instrument cluster that control the fuel gauge, a DRB III scan tool is required. Refer to the appropriate diagnostic information.

GEAR SELECTOR INDICATOR
An electronic automatic transmission gear selector indicator is standard factory-installed equipment on this model, when it is also equipped with an optional automatic transmission. The gear selector indicator information is displayed in a Vacuum-Fluorescent Display (VFD), which is visible through a small window cutout located in the lower right quadrant of the cluster overlay. The gear selector indicator displays the following characters from left to right:"P," "N," "D," "2," and "1." Respectively, these characters represent the park, reverse, neutral, drive, second gear, and first gear positions of the transmission gear selector lever on the steering column. The VFD illuminates a rectangular box around the character that represents the currently selected lever position.

During daylight hours (exterior lamps OFF) the gear selector indicator 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 thumbwheel on the headlamp switch. However, a "Parade" mode position of the panel lamps dimmer thumbwheel allows the VFD to be illuminated at full brightness while the exterior lamps are turned ON during daylight hours. The gear selector indicator VFD is serviced as a unit with the instrument cluster.

The electronic gear selector indicator gives an indication to the vehicle operator of the transmission gear that has been selected with the automatic transmission gear selector lever. This gauge is controlled by the instrument cluster circuit board based upon cluster programming. The cluster circuitry automatically configures itself for the proper automatic transmission model based upon the hard wired transmission range sensor MUX circuit input to the cluster. Each time the cluster is disconnected from battery current for more than about five minutes, it must configure itself again for the automatic transmission model that is in the vehicle when it is reconnected to battery current. The gear selector indicator information is displayed by a dedicated Vacuum Fluorescent Display (VFD) on the instrument cluster electronic circuit board, and the VFD will not display the gear selector indicator information after the ignition switch is turned to the Off position. The instrument cluster circuitry configures the gear selector indicator VFD based upon the following inputs from the transmission range sensor:

- Open Circuit - If the transmission range sensor MUX circuit is open, the cluster circuitry controls the gear selector indicator display based upon electronic messages received from the electronic Transmission Control Module (TCM) over the Programmable Communications Interface PCI data bus. If the input is open circuit and no electronic messages are received from the TCM within two seconds, the instrument cluster circuitry will cycle the indicated gear selector position from P, to R, to N, to D to 2 repeatedly and continuously until the condition is resolved or until the ignition switch is turned to the Off position, whichever occurs first.

- Resolved Circuit - If the transmission range sensor MUX circuit is resolved, the cluster circuitry controls the gear selector indicator display based upon the resistance value of the hard wired input from the transmission range sensor. If the cluster has configured itself for the transmission range sensor input and detects a short to ground in the transmission range sensor MUX input, the cluster will indicate all positions in the VFD; or, if this input is open circuit, the cluster will blink all positions in the VFD. The VFD display for the short-to-ground and open circuit conditions will continue until the condition is resolved or until the ignition switch is turned to the Off position, whichever occurs first.

- Actuator Test - Each time the cluster is put through the actuator test, the VFD will display all of its characters at once, then step through each character segment individually during the VFD portion of the test to confirm the functionality of the VFD and the cluster control circuitry.

On models with a TCM, the TCM continually monitors the transmission range sensor, then sends the proper gear selector indicator messages to the instrument cluster. On models without a TCM, the instrument cluster continually monitors the hard wired transmission range sensor multiplexed input. For further diagnosis of the gear selector indicator or the instrument cluster circuitry that controls this function, (Refer to INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING). On models with a TCM, for proper diagnosis of the transmission range sensor, the TCM, the PCI data bus, or the message inputs to the instrument cluster that control the gear selector indicator, a DRB III scan tool is required. Refer to the appropriate diagnostic information.

HIGH BEAM INDICATOR
A high beam indicator is standard equipment on all instrument clusters. The high beam indicator is located near the upper edge of the instrument cluster overlay, between the tachometer and the speedometer. The high beam indicator consists of a stenciled cutout of the International Control and Display Symbol icon for "High Beam" in the opaque layer of the instrument cluster overlay. The dark outer layer of the overlay prevents the indicator from being clearly visible when it is not illuminated. A blue lens behind the cutout in the opaque layer of the overlay causes the icon to appear in blue when it is illuminated from behind by a replaceable incandescent bulb and bulb holder unit located on the instrument cluster electronic circuit board, The high beam indicator is serviced as a unit with the instrument cluster.

The high beam indicator gives an indication to the vehicle operator when the headlamp high beams are illuminated. This indicator is hard wired on the instrument cluster electronic circuit board, and is controlled by the Central Timer Module (CTM) through the high beam indicator driver circuit input to the cluster based upon a control signal to the CTM from the headlamp beam select switch. The headlamp beam select switch is integral to the multi-function switch on the left side of the steering column. The high beam indicator bulb receives battery current on the instrument cluster electronic circuit board through a fused B(+) circuit at all times; therefore, the indicator remains operational regardless of the ignition switch position. The indicator only illuminates when it is provided with a path to ground by the CTM. The high beam indicator can be diagnosed using conventional diagnostic tools and methods. For proper diagnosis of the CTM and the inputs to the CTM that control the high beam indicator driver circuit, a DRB III scan tool is required. Refer to the appropriate diagnostic information.