Part 7 of 8

MALFUNCTION INDICATOR LAMP
A Malfunction Indicator Lamp (MIL) is standard equipment on all instrument clusters. The MIL is located in the Information Center area of the instrument cluster overlay, to the left of center. The MIL consists of a stencilled cutout of the International Control and Display Symbol icon for "Engine" 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. An amber lens behind the cutout in the opaque layer of the overlay causes the icon to appear in amber through the translucent outer layer of the overlay when the indicator is illuminated from behind by a Light Emitting Diode (LED) soldered onto the instrument cluster electronic circuit board. The MIL is serviced as a unit with the instrument cluster.

The Malfunction Indicator Lamp (MIL) gives an indication to the vehicle operator when the Powertrain Control Module (PCM) has recorded a Diagnostic Trouble Code (DTC) for an On-Board Diagnostics II (OBD II) emissions-related circuit or component malfunction. The MIL is controlled by a transistor on the instrument cluster circuit board based upon cluster programming and electronic messages received by the cluster from the PCM over the Programmable Communications Interface (PCI) data bus. The MIL Light Emitting Diode (LED) 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; therefore, the LED will always be OFF when the ignition switch is in any position except ON or Start. The LED only illuminates when it is provided a path to ground by the instrument cluster transistor. The instrument cluster will turn ON the MIL for the following reasons:

- Bulb Test - Each time the ignition switch is turned to the ON position the indicator is illuminated for about seven seconds as a bulb test.

- PCM Lamp-ON Message - Each time the cluster receives a lamp-ON message from the PCM, the indicator will be illuminated. The indicator can be flashed ON and OFF, or illuminated solid, as dictated by the PCM message. For some DTC's, if a problem does not recur, the PCM will send a lamp-OFF message automatically. Other DTC's may require that a fault be repaired and the PCM be reset before a lamp-OFF message will be sent. For more information on the PCM, and the DTC set and reset parameters, (Refer to EMISSIONS CONTROL - OPERATION).

- Communication Error - If the cluster receives no lamp-ON message from the PCM for twenty seconds, the MIL is illuminated by the instrument cluster to indicate a loss of bus communication. The indicator remains controlled and illuminated by the cluster until a valid lamp-ON message is received from the PCM.

- Actuator Test - Each time the cluster is put through the actuator test, the indicator will be turned ON during the bulb check portion of the test to confirm the functionality of the LED and the cluster control circuitry.

The PCM continually monitors the fuel and emissions system circuits and sensors to decide whether the system is in good operating condition. The PCM then sends the proper lamp-ON or lamp-OFF messages to the instrument cluster. For further diagnosis of the MIL or the instrument cluster circuitry that controls the LED, (Refer to INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING). If the instrument cluster turns ON the MIL after the bulb test, it may indicate that a malfunction has occurred and that the fuel and emissions systems may require service. For proper diagnosis of the fuel and emissions systems, the PCM, the PCI data bus, or the message inputs to the instrument cluster that control the MIL, a DRB III scan tool is required. Refer to the appropriate diagnostic information.

ODOMETER
An odometer and trip odometer are standard equipment in all instrument clusters. The odometer and trip odometer information are displayed in a common electronic Vacuum-Fluorescent Display (VFD), which is visible through a small window cutout located in the left lower quadrant of the cluster overlay. 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 knob that extends through the lower edge of the cluster lens, just right of the odometer VFD. When the trip odometer information is displayed, the word "TRIP" is also illuminated in a green color and at the same lighting level as the trip odometer information in the lower right corner of the VFD. Both the odometer and the trip odometer information is stored in the instrument cluster memory.

The odometer can display values up to 499,999 kilometers (499,999 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), the trip odometer display does have a decimal point and will show tenths of a unit (kilometer or mile). The unit of measure (kilometers or miles) 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. During daylight hours (exterior lamps OFF) 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 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 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 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 odometer and trip odometer information is displayed by the instrument cluster Vacuum Fluorescent Display (VFD), and the VFD will not display odometer or trip odometer information after the ignition switch is 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 momentarily with the ignition switch in the ON position will toggle the VFD between the odometer and trip odometer display. Each time the ignition switch is turned to the ON position the VFD will automatically return to the mode (odometer or trip odometer) last displayed when the ignition switch was turned to the OFF position.

- Trip Odometer Reset - When the trip odometer reset switch is pressed and held for longer than about two seconds, the trip odometer will be reset to 000.0 kilometers (miles). The VFD must be displaying the trip odometer information in order for the trip odometer information to be reset.

- Message Failure - If the cluster fails to receive a distance message during normal operation, it will flash the odometer/trip odometer distance information ON and OFF repeatedly until a distance message is received, or until the ignition switch is turned to the OFF position, whichever occurs first. 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 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 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.

The PCM continually monitors 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 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.

OIL PRESSURE GAUGE
An oil pressure gauge is standard equipment on all instrument clusters. The oil pressure gauge is located in the upper right quadrant of the instrument cluster, above the fuel gauge. The oil pressure 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 "L" (or Low) to "H" (or High). An International Control and Display Symbol icon for "Engine Oil" is located on the cluster overlay, in the center of the gauge directly above the hub of the gauge needle. The oil pressure 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 oil pressure gauge is serviced as a unit with the instrument cluster.

The oil pressure gauge gives an indication to the vehicle operator of the engine oil pressure. 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 oil pressure 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:

- Engine Oil Pressure Message - The instrument cluster circuitry restricts the oil pressure gauge needle operation in order to provide readings that are consistent with customer expectations. Each time the cluster receives a message from the PCM indicating the engine oil pressure is between about 6.9 kPa (1 psi) and 137.9 kPa (20 psi), the cluster holds the gauge needle at a point about 11 degrees above the low end of normal increment on the gauge scale. Each time the cluster receives a message from the PCM indicating the engine oil pressure is between about 517.1 kPa (75 psi) and 755 kPa (109.5 psi), the cluster holds the gauge needle at a point about 7.4 degrees below the high end of normal increment on the gauge scale. When the cluster receives messages from the PCM indicating the engine oil pressure is between about 137.9 kPa (20 psi) and 517.1 kPa (75 psi), the gauge needle is moved to the actual pressure position on the gauge scale.

- Engine Oil Pressure Low Message - Each time the cluster receives a message from the PCM indicating the engine oil pressure is below about 6.9 kPa (1 psi), the gauge needle is moved to the L (Low) graduation at the far left end of the gauge scale, the check gauges indicator is illuminated, and a single chime tone is generated. The gauge needle remains at the low end of the scale and the check gauges indicator remains illuminated until the cluster receives a message from the PCM indicating that the engine oil pressure is above about 6.9 kPa (1 psi), or until the ignition switch is turned to the OFF position, whichever occurs first. The cluster will only turn the check gauges indicator lamp ON in response to an engine oil pressure low message if the engine speed message is greater than zero.

- Engine Oil Pressure High Message - Each time the cluster receives a message from the PCM indicating the engine oil pressure is above about 755 kPa (109.5 psi), the gauge needle is moved to the H (High) graduation at the far right end of the gauge scale. The gauge needle remains at the high end of the scale until the cluster receives a message from the PCM indicating that the engine oil pressure is below about 755 kPa (109.5 psi), or until the ignition switch is turned to the OFF position, whichever occurs first.

- Message Failure - If the cluster fails to receive an engine oil pressure 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 engine oil pressure sensor to determine the engine oil pressure. The PCM then sends the proper engine oil pressure messages to the instrument cluster. For further diagnosis of the oil pressure gauge or the instrument cluster circuitry that controls the gauge, (Refer to INSTRUMENT CLUSTER - DIAGNOSIS AND TESTING). If the instrument cluster turns ON the check gauges indicator due to a low oil pressure gauge reading, it may indicate that the engine or the engine oiling system requires service. For proper diagnosis of the engine oil pressure sensor, the PCM, the PCI data bus, or the message inputs to the instrument cluster that control the oil pressure gauge, a DRB III scan tool is required. Refer to the appropriate diagnostic information.