Part 1

SYSTEM OPERATION
Coolant Temperature Gauge
The coolant temperature gauge gives an indication of the engine coolant temperature. The instrument cluster circuitry controls the gauge pointer position. The instrument cluster circuitry calculates the proper gauge pointer position based upon engine coolant temperature messages received from the Powertrain Control Module (PCM) on the Chrysler Collision Detection (CCD) data bus.

The PCM uses an input from the engine coolant temperature sensor and internal programming to decide what engine coolant temperature messages are required. The PCM then sends the proper messages to the instrument cluster on the CCD data bus.

If the PCM messages indicate that coolant temperature is too high, the instrument cluster circuitry moves the gauge needle to the high end of the scale on the gauge face, turns on the Check Gauges lamp, and sends a chime tone request to the Central Timer Module (CTM).

The engine coolant temperature sensor is installed in a threaded hole that penetrates a coolant passage of the engine. It is a thermistor-type sensor that changes its internal resistance with changes in engine coolant temperature.

Fuel Gauge
The fuel gauge gives an indication of the level of fuel in the fuel tank. The instrument cluster circuitry controls the gauge pointer position. The instrument cluster circuitry calculates the proper gauge pointer position based upon fuel level messages received from the Powertrain Control Module (PCM) on the Chrysler Collision Detection (CCD) data bus.

The PCM uses an input from the fuel gauge sending unit and internal programming to decide what fuel level messages are required. The PCM then sends the proper messages to the instrument cluster on the CCD data bus. If the PCM messages indicate that the fuel level is below one-eighth of a full tank for more than ten seconds (60 seconds if the vehicle speed input is greater than zero miles-per-hour), the instrument cluster circuitry turns on the low fuel warning lamp and sends a chime tone request to the Central Timer Module (CTM).

The fuel gauge sending unit is mounted to the electric fuel pump module located inside the fuel tank. The sending unit has a float attached to the end of a swing-arm. The float moves up or down within the fuel tank as the fuel level changes. As the float moves, an electrical contact on the pivot end of the swing-arm wipes across a resistor coil, which changes the internal electrical resistance of the sending unit.

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.

Oil Pressure Gauge
The oil pressure gauge gives an indication of the engine oil pressure. The instrument cluster circuitry controls the gauge pointer position. The instrument cluster circuitry calculates the proper gauge pointer position based upon engine oil pressure messages received from the Powertrain Control Module (PCM) on the Chrysler Collision Detection (CCD) data bus.

The PCM uses an input from the engine oil pressure sensor and internal programming to decide what engine oil pressure messages are required. The PCM then sends the proper messages to the instrument cluster on the CCD data bus. If the PCM messages indicate that oil pressure is too low, the instrument cluster circuitry moves the gauge needle to the 0 PSI graduation on the gauge face, turns on the Check Gauges lamp, and sends a chime tone request to the Central Timer Module (CTM). If the PCM messages indicate that oil pressure is too high, the instrument cluster circuitry moves the gauge needle to the 110 PSI graduation on the gauge face.

The engine oil pressure sensor is installed in a threaded hole that penetrates an oil passage of the engine. The engine oil pressure sensor contains a flexible diaphragm and a variable resistor coil. The diaphragm moves in response to changes in the engine oil pressure, which changes the internal electrical resistance of the sensor.

Speedometer
The speedometer gives an indication of the current vehicle speed. The instrument cluster circuitry controls the gauge pointer position. The instrument cluster circuitry calculates the proper gauge pointer position based upon vehicle speed 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 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 speedometer readings. For diagnosis of the speedometer inputs, a DRB scan tool and the proper Diagnostic Procedures are recommended.

Voltmeter
The voltmeter gives an indication of the electrical system voltage. The instrument cluster circuitry controls the gauge pointer position. The instrument cluster circuitry calculates the proper gauge pointer position based upon system voltage messages received from the Powertrain Control Module (PCM) on the Chrysler Collision Detection (CCD) data bus.

The PCM uses an input from the electrical system and internal programming to decide what system voltage messages are required. The PCM then sends the proper messages to the instrument cluster on the CCD data bus. If the PCM messages indicate that the charging system has failed, the electrical system voltage is less than 11 volts or greater than 16.6 volts, the instrument cluster circuitry turns on the Check Gauges lamp and sends a chime tone request to the Central Timer Module (CTM). Refer to Starting and Charging/Charging Systems for more information on the charging system components and their diagnosis.

Airbag Indicator Lamp
The airbag indicator lamp gives an indication when the airbag system is faulty or inoperative. The lamp is controlled by the instrument cluster circuitry based upon messages received from the Airbag Control Module (ACM) on the Chrysler Collision Detection (CCD) data bus. The lamp is turned on by the ACM for about seven seconds when the ignition switch is turned to the On position as a bulb test.

The ACM continually monitors the airbag system circuits and sensors to decide whether the system is in good operating condition. The ACM then sends the proper messages to the instrument cluster on the CCD data bus to turn the lamp on or off. If the ACM turns the lamp on after the bulb test, it indicates the ACM has detected a system malfunction and/or that the airbag system has become inoperative. The instrument cluster circuitry will also send a chime request to the Central Timer Module (CTM) when a lamp-on message is received from the ACM. A lamp-on message does not mean that either or both airbags will not deploy upon an impact, only that they might not deploy, depending upon the nature of the detected malfunction. Each time that the instrument cluster circuitry receives a lamp-on message from the ACM, it will light the lamp for three seconds or the duration of the airbag system malfunction, whichever is longer.

The airbag indicator lamp also has a lamp backup feature. About ten seconds after the ignition switch is turned to the On position, if an inoperative airbag warning lamp circuit was detected during the bulb test sequence, the instrument cluster circuitry will flash the seat belt reminder lamp on and off for about thirty seconds. If the seat belt reminder lamp stays on after flashing for thirty seconds, or comes on at any time other than about ten seconds after the initial ignition-on sequence, it may indicate that an airbag system fault has been detected and that the airbag indicator lamp is inoperative.

See Seat Belt Reminder Lamp in the Description and Operation for more information on the airbag lamp backup feature. Refer to AIRBAG System in Air Bags and Seat Belts/Air Bags for more information on the airbag system.

Anti-Lock Brake System Lamp
The Anti-Lock Brake System (ABS) lamp gives an indication when the ABS system is faulty or inoperative. The lamp is controlled by the instrument cluster circuitry based upon messages received from the Controller Anti-lock Brake (CAB) on the Chrysler Collision Detection (CCD) data bus. The lamp is turned on by the CAB for about two seconds when the ignition switch is turned to the On position as a bulb test.

After the bulb test, the CAB turns the lamp on or off based upon the results of the ABS self-tests. The CAB continually monitors the ABS circuits and sensors to decide whether the system is in good operating condition. The CAB then sends the proper messages to the instrument cluster on the CCD data bus to turn the lamp on or off. If the CAB turns the lamp on after the bulb test, it indicates that the CAB has detected a system malfunction and/or that the ABS system has become inoperative. If only the amber ABS lamp is illuminated, and the red brake warning lamp remains off, the base brake system will operate normally.

Each time the instrument cluster circuitry receives a lamp-on message from the CAB, it will light the lamp for the duration of the ABS malfunction. The CAB will also flash this lamp during the diagnostic mode, unless a hard fault is present. If a hard fault is present, the ABS lamp will illuminate without flashing.

Brake Warning Lamp
The brake warning lamp gives an indication when the parking brake is applied, when the pressures in the two halves of the split brake hydraulic system are unequal, if the Anti-lock Brake System (ABS) lamp has failed and an ABS fault occurs, and during ABS diagnostics. The lamp is turned on by the instrument cluster circuitry for about two seconds when the ignition switch is moved to the Start position as a bulb test. After the bulb test, the lamp is controlled by a hard wired input from the parking brake switch and/or by the instrument cluster circuitry based upon messages received from the Controller Anti-lock Brake (CAB) on the Chrysler Collision Detection (CCD) data bus.

The CAB turns the lamp on or off based upon the results of the ABS self-tests. The CAB continually monitors the ABS circuits and sensors, including the brake warning switch and the ABS lamp, to decide whether the system is in good operating condition. The CAB then sends the proper messages to the instrument cluster on the CCD data bus to turn the lamp on or off. If the CAB turns the lamp on after the bulb test, it indicates that the CAB has detected a system malfunction.

The parking brake switch is hard wired to the instrument cluster and closes to ground when the parking brake is applied. The brake warning switch is hard wired to the CAB and closes to ground when it senses unequal hydraulic pressures in the two halves of the split brake hydraulic system, possibly due to low brake fluid level or brake fluid leakage.

After the bulb test, if the red brake warning lamp remains illuminated with the parking brake released, the base brake system may not be operational. The vehicle should never be operated while the red brake warning lamp is illuminated.

Check Gauges Lamp
The check gauges lamp gives an indication when certain gauges reflect a condition requiring immediate attention. The lamp is turned on by the instrument cluster circuitry for about three seconds after the ignition switch is turned to the On position as a bulb test. After the bulb test, the lamp is controlled by the instrument cluster circuitry based upon gauge data messages received from the Powertrain Control Module (PCM) on the Chrysler Collision Detection (CCD) data bus.

The PCM uses several inputs to decide what gauge data messages are required. The PCM then sends the proper message to the instrument cluster on the CCD data bus. When the instrument cluster circuitry receives a gauge data message that requires the check gauges lamp to be turned on, it also sends a chime tone request to the Central Timer Module (CTM).

The gauge data messages for which the instrument cluster is programmed to turn on the check gauges lamp are:
- Engine coolant temperature is high
- Engine oil pressure is low
- System voltage is high or low.