Principles of Operation (How Does It Work?)

PRINCIPLES OF OPERATION

The instrument cluster is a configurable, hybrid electronic cluster (HEC) that contains a microprocessor, gauges, indicator lamps, and internal circuitry. The instrument cluster is non-repairable with the exception of the instrument cluster lens. The instrument cluster utilizes hardwired circuitry, the standard corporate protocol (SCP), and universal asynchronous receiver transmitter (UART) based protocol (UBP) communication networks. Communication using the SCP network transmits and receives data between the instrument cluster the PCM, electronic automatic temperature control (EATC), and the anti-lock brake system/traction control/integrated vehicle dynamics (ABS/TC/IVD) module. Communication using the UBP network utilizes data transmitted and received by the instrument cluster and the 4x4 control module, parking aid module, vehicle security module, and the driver seat module.

Instrument Cluster Replacement
When installing a new instrument cluster, contact the Instrument Cluster Program.

CAUTION: When installing a new instrument cluster, the instrument cluster must be re-configured.

It is very important to understand:
- where the input originates from.
- all the information necessary in order for a feature to operate.
- which module(s) receive(s) the input or command message.
- whether the module which received the input controls the output of the feature, or whether it outputs a message over the SCP or UBP network to another module.
- which module controls the output of the feature.

The instrument cluster carries out a display prove-out to verify that the warning/indicator lamps and monitored systems are operating correctly. When the key is turned to the ON position with the engine off, the following indicators will illuminate:
- 4x4 HIGH indicator
- 4x4 LOW indicator
- AWD LOCK (if equipped)
- ABS warning indicator
- air bag warning indicator
- BRAKE warning indicator
- check gauge warning indicator
- LOW WASH indicator
- traction control indicator
- check fuel cap indicator
- safety belt warning indicator
- door ajar indicator

Integrated Circuit Display
The integrated circuit display is a vacuum fluorescent tube display that contains the odometer, trip odometer, outside air temperature and compass display on base clusters and the message center display on message center clusters. For additional information on the message center, refer to Information And Message Center. The compass module and outside air temperature sensor are hardwired to the instrument cluster. The odometer information is transmitted from the PCM through the SCP communication network to the instrument cluster. The instrument cluster displays the appropriate message(s) upon receipt of the outside air temperature, compass heading and odometer data received.

Gauges

Speedometer
The instrument cluster receives the vehicle speed sensor (VSS) signal from the powertrain control module (PCM) through the standard corporate protocol (SCP) communication network. The instrument cluster monitors the VSS input from the PCM and commands the speedometer with a corresponding movement of the pointer.

Odometer
The odometer and trip odometer are viewed through the message center in the integrated circuit display on message center clusters or in the integrated circuit display on base clusters. The odometer is tamper-resistant and accumulates and registers up to one million miles in English mode or one million kilometers in metric mode, based upon rolling count data sent from the PCM via the SCP network. The trip odometer is resettable and accumulates and registers up to 1,608 kilometers (999 miles).

Fuel Gauge
The fuel gauge receives its signal from the fuel level sensor, part of the fuel pump module. The fuel level sensor measures variable resistance in the fuel tank depending on the current fuel level. When the fuel level is low, resistance in the unit is low (15 ohms ± 1 ohm). When the fuel level is high, the resistance is high (160 ohms ± 2 ohms). If equipped with flex-fuel, the basic fuel level indication is the same except that the flex-fuel vehicles incorporate the use of a flex-fuel module. The flex-fuel module is a DC-AC-DC interface, used to prevent reactions created by the interaction of DC current with the fuel. The flex-fuel module is part of the fuel pump module and is installed as an assembly.

Temperature Gauge
The PCM receives the engine coolant temperature status through hardwired circuitry to the engine coolant temperature (ECT) sensor. The instrument cluster receives the engine coolant temperature data from the PCM through the SCP communication network. The instrument cluster monitors the engine coolant temperature data received from the PCM and commands the temperature gauge indication with a corresponding movement of the pointer. If the instrument cluster receives no signal the temperature gauge will default to the cold position.

Oil Pressure Gauge
The instrument cluster is hardwired to the engine oil pressure switch. The engine oil pressure switch consists of a diaphragm and contact points, which are normally open. When there is low or no oil pressure, the engine oil pressure switch remains open and removes the ground to the instrument cluster and when sufficient oil pressure exists, the engine oil pressure switch closes providing a ground signal to the instrument cluster. The instrument cluster monitors the oil pressure and commands the oil pressure gauge indication with a corresponding pointer movement.

Voltage Gauge
The voltage gauge displays the system battery voltage as measured at the instrument cluster run input.

Tachometer
The tachometer is electrically operated and indicates engine speed in revolutions per minute (rpm). The tachometer range is 0 to 7,000 rpm. The tachometer receives the signal through the SCP network from the PCM. If the rpm information sent to the instrument cluster is invalid or missing, the instrument cluster will default the tachometer to 0 rpm.

Warning Indicator Lamps

Air Bag Warning Indicator
The instrument cluster is hardwired to the restraint control module. If an air bag system concern is detected, a DTC is logged and the restraint control module provides a ground path to the instrument cluster turning on the air bag indicator.

Anti-Lock Brake System (ABS) Warning Indicator
The ABS warning indicator is used to indicate an ABS concern or deactivation of the ABS. The instrument cluster, upon receipt of the ABS message from the ABS module through the SCP communication network, turns on the ABS warning indicator.

BRAKE Warning Indicator
The parking brake switch is hardwired to the instrument cluster and the brake fluid level switch is hardwired to the ABS module. The instrument cluster BRAKE warning indicator utilizes two inputs. The first input is provided by the parking brake switch and when applied, provides a ground to the instrument cluster turning on the BRAKE warning indicator. The second input is controlled by the ABS module. The ABS module, upon receipt of a low brake fluid level signal or base brake system concern, provides a brake signal to the instrument cluster through the SCP communication network. The instrument cluster upon receipt of the brake signal, turns on or off the BRAKE warning indicator according to the monitored data.

Charging System Warning Indicator
The instrument cluster receives the charge signal from the PCM through the SCP network. When the generator output is insufficient to maintain the battery state of charge the instrument cluster will illuminate the charging system indicator.

Check Gauge Warning Indicator
The check gauge warning indicator will illuminate when any of the following conditions exist: the engine oil pressure drops below approximately 42 kPa (6 psi), the engine temperature exceeds approximately 118°C (244°F), the fuel level drops below approximately 15 percent of fuel system capacity (base cluster only).

Door Ajar Warning Indicator (Base Cluster)
The door ajar switches provide a ground signal to the vehicle security module. The vehicle security module, upon receipt of the door ajar ground data, supplies a door ajar status message to the instrument cluster through the UBP communication network. The instrument cluster monitors the door ajar status and commands the door ajar indicator on or off according to the door ajar status message.

Safety Belt Warning Indicator
The restraint control module monitors the safety belt position through the safety belt switch (part of the buckle). When the safety belt is buckled, the restraint control module receives a ground signal and sends an SCP message to the instrument cluster to turn off the safety belt warning indicator. When the safety belt is unbuckled, the ground to the restraint control module is removed and the restraint control module sends an SCP safety belt warning message to the instrument cluster to turn on the indicator.

Indicator Lamps

CHECK FUEL CAP Indicator (Base Cluster)
The check fuel cap indicator is used to indicate significant leaks in the fuel tank evaporative system due to a loose fuel cap or other fuel evaporative system concerns. Fuel tank pressure is monitored by the PCM and once a leak is detected, the PCM signals a fault to the instrument cluster through the SCP network. Once the PCM has detected a loose fuel cap and the check fuel cap indicator is illuminated, the check fuel cap indicator will remain illuminated until the fuel cap is secured and the vehicle has been running for several minutes or the ignition has been cycled once.

High Beam Indicator
The instrument cluster provides a ground for the high beam indicator. When the high beams are turned on, the multifunction switch provides a power signal to the instrument cluster through hardwired circuitry and illuminates the high beam indicator.

Low Washer Fluid Indicator (Base Cluster)
The instrument cluster is hardwired to the low washer fluid switch. The low washer fluid switch closes and provides a ground to the instrument cluster when the washer fluid is low, turning on the low washer fluid indicator. When the washer fluid is above the low level, the low washer fluid switch opens and removes the ground to the instrument cluster and the low washer fluid indicator turns off.

O/D OFF Indicator
The instrument cluster receives the overdrive off signal from the PCM through the SCP communication network. The overdrive off switch is hardwired to the PCM. When the transmission overdrive is selected off, the overdrive off switch provides a ground signal to the PCM. The PCM, upon receipt of the overdrive off ground signal, provides an SCP overdrive off signal to the instrument cluster and the instrument cluster will turn on the O/D OFF indicator.

RH and LH Turn Indicators
The instrument cluster provides a ground for the RH and LH turn indicators. When the multifunction switch is in the RH or LH turn position, power is supplied to the instrument cluster through hardwired circuitry and the RH or LH turn indicators flash on and off.

SERVICE ENGINE SOON Indicator
The malfunction indicator lamp indicator is illuminated when a diagnostic trouble code (DTC) is detected by the powertrain control module (PCM). The instrument cluster receives the MIL data from the PCM through the SCP network.

Speed Control Indicator
The instrument cluster receives the speed control signal from the PCM through the SCP communication network. When the speed control is engaged, the PCM provides a ground to the instrument cluster and turns on the speed control indicator.

Traction Control Indicator (Message Center Cluster)
The traction control indicator flashes when the vehicle traction control is in active mode or is being controlled by the ABS/TC/IVD module. The instrument cluster receives the traction control signal from the anti-lock brake system/traction control/integrated vehicle dynamics (ABS/TC/IVD) module through the UBP communication network. The instrument cluster monitors the traction control signal and when the ABS/TC/IVD module detects a traction control concern, the instrument cluster will turn on the traction control indicator.

4x4 HIGH and 4x4 LOW Indicators
The instrument cluster receives the 4x4 HIGH and 4x4 LOW information from the four-wheel drive module through the UPB communication network. When either 4x4 high or 4x4 low are selected, the four-wheel drive control module will provide a 4x4 status signal to the instrument cluster and turn on the appropriate indicator.

AWD LOCK (if equipped)
The instrument cluster receives the AWD indicator status from the 4x4 control module. When all-wheel drive is selected, the 4x4 control module provides an indicator on command over the UBP communication network to the instrument cluster to turn on the AWD LOCK indicator.