Part 1
SYSTEM OPERATIONCoolant 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 an engine coolant temperature message 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 message is required. The PCM then sends the proper message to the instrument cluster on the CCD data bus.
If the PCM message indicates that coolant temperature is high, the instrument cluster circuitry moves the gauge needle into the beginning of the red zone on the gauge face, turns on the Check Gauges lamp, and generates a single chime tone. If the PCM message indicates that coolant temperature is critical, the instrument cluster circuitry moves the gauge needle to the stop at the end of the red zone on the gauge face.
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. Refer to Powertrain Management/Computer and Control Systems for more information on the PCM and the coolant temperature sensor.
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 a fuel level message 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 message is required. The PCM then sends the proper message to the instrument cluster on the CCD data bus. If the vehicle is equipped with the high-line instrument cluster, when the PCM message indicates that the fuel level is below one-eighth of a full tank, the instrument cluster circuitry turns on the low fuel warning lamp and generates a single chime tone.
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 The Trip Odometer
The odometer and the trip odometer share the same vacuum fluorescent digital display tube in 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 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 on distance pulse messages received from the Powertrain Control Module (PCM) on the Chrysler Collision Detection (CCD) data bus.
The PCM uses an input from the Vehicle Speed Sensor (VSS) and internal programming to decide what distance pulse signal is required. The PCM then sends the proper message to the instrument cluster circuitry on the CCD data bus. The instrument cluster stores both the odometer and trip odometer distance information and displays the proper value based upon ignition key-on and trip odometer reset knob inputs. The instrument cluster also stores the odometer display mode (odometer or trip odometer), and will return to the mode that was selected prior to the ignition switch being turned off.
If the instrument cluster is not receiving distance information on the CCD data bus when the ignition switch is turned to the On position, the odometer display will remain blank. If the instrument cluster does not receive a distance message on the CCD data bus after the ignition switch has been turned to the On position, the instrument panel circuitry will insert the last normally displayed distance in the odometer display. If the instrument cluster is receiving CCD messages, but cannot display odometer values due to an internal error, the odometer display will be blank.
The VSS is a hall-effect sensor that is installed in the transmission (two-wheel drive) or transfer case (four-wheel drive), and is driven by the output shaft through a speedometer pinion gear. Incorrect tire size, incorrect axle ratio, a faulty or incorrect speedometer pinion gear, or a faulty VSS can each result in inaccurate odometer readings. Refer to Powertrain Management/Computer and Control systems for more information on the PCM and the VSS. Refer to Transmission and Drivetrain for more information on the speedometer pinion gear.
The odometer and trip odometer can also be used to digitally display a stored DTC. Refer to Powertrain Management/Computer and Control systems for more information on DTCs and their retrieval.
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 an engine oil pressure message 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 message is required. The PCM then sends the proper message to the instrument cluster on the CCD data bus. If the PCM message indicates that oil pressure is low, the instrument cluster circuitry moves the gauge needle to below the zero graduation on the gauge face, and turns on the Check Gauges lamp.
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 a vehicle speed message received from the Powertrain Control Module (PCM) on the Chrysler Collision Detection (CCD) data bus.
The PCM uses an input from the Vehicle Speed Sensor (VSS) and internal programming to decide what vehicle speed message is required. The PCM then sends the proper message to the instrument cluster on the CCD data bus.
The VSS is a hall-effect sensor that is installed in the transmission (two-wheel drive) or transfer case (four-wheel drive), and is driven by the output shaft through a speedometer pinion gear. Incorrect tire size, incorrect axle ratio, a faulty or incorrect speedometer pinion gear, or a faulty VSS can each result in inaccurate speedometer readings. Refer to Powertrain Management/Computer and Control Systems for more information on the PCM and the VSS. Refer to Transmission and Drivetrain for more information on the speedometer pinion gear.
Tachometer
The tachometer gives an indication of the engine speed in revolutions-per-minute (RPM). The instrument cluster circuitry controls the gauge pointer position. The instrument cluster circuitry calculates the proper gauge pointer position based upon an engine speed message received from the Powertrain Control Module (PCM) on the Chrysler Collision Detection (CCD) data bus.
The PCM uses an input from the crankshaft position sensor and internal programming to calculate what engine speed message is required. The PCM then sends the proper message to the instrument cluster on the CCD data bus. The crankshaft position sensor is a hall-effect sensor installed near the rear of the engine, where it is aimed at the trigger wheel attached to the rear flange of the crankshaft.
Refer to Powertrain Managemen/Computer and Control System for more information on the PCM. Refer to Powertrain Management/Computer and Control System for more information on the crankshaft position sensor.
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 a system voltage message 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 message is required. The PCM then sends the proper message to the instrument cluster on the CCD data bus.
If the PCM message indicates that the charging system has failed, the instrument cluster circuitry moves the gauge needle to the 9 Volt graduation on the gauge face, and turns on the Check Gauges lamp. If the PCM message indicates that system voltage is high, the instrument cluster circuitry moves the gauge needle to the 19 Volt graduation on the gauge face, and turns on the Check Gauges lamp.
Refer to Powertrain Management/Computer and Control Systems for more information on the PCM. Refer to Starting and Charging/Charging Systems for more information on charging system components and diagnosis.
Airbag Indicator Lamp
The airbag indicator lamp gives an indication when the airbag system is faulty or inoperative. The lamp is turned on by the instrument cluster circuitry for about seven seconds when 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 a message received from the Airbag Control Module (ACM) on the Chrysler Collision Detection (CCD) data bus.
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 message to the instrument cluster on the CCD data bus to turn the lamp on or off. If the ACM sends a lamp-on message after the bulb test, it indicates that the ACM has detected a system malfunction and/or that the airbag system has become inoperative.
Each time the instrument cluster circuitry receives a lamp-on message from the ACM, it will light the lamp for twelve seconds or the duration of the airbag system malfunction, whichever is longer. If the instrument cluster receives no lamp messages from the ACM for more than five seconds, it will light the lamp for twelve seconds or until another lamp-off message from the ACM, whichever is longer.
Refer to Air Bags and Seat Belts/Air Bag 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 hard-wired in the instrument cluster, and is completely controlled by the Controller Anti-lock Brake (CAB). It receives battery voltage through the instrument cluster fused ignition switch output feed circuit, and is grounded by the CAB. 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 system self-tests.
The CAB continually monitors the ABS circuits and sensors to decide whether the system is in good operating condition. 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. Refer to Brakes and Traction Control/Brakes/Anti-Lock Brake System for more information.
Brake Warning Lamp
The brake warning lamp gives an indication when the parking brake is applied, or when the pressures in the two halves of the split brake hydraulic system are unequal. The lamp is turned on when the ignition switch is in the Start position as a bulb test. After the bulb test, the lamp is controlled by hard-wired inputs from the parking brake switch and/or the brake warning switch.
The brake warning switch 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. The parking brake switch closes to ground when the parking brake is applied. Refer to Brakes and Traction Control/Brakes/Anti-Lock Brake System for more information.
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. The gauge data messages for which the instrument cluster is programmed to turn on the check gauges lamp are:
- Engine coolant temperature is high or critical
- Engine oil pressure is low
- Charging system failure
- System voltage is high.