Principles of Operation (How Does It Work?)

NOTE:
- The instrument cluster, front electronic module (FEM), and the rear electronic module (REM) must be reconfigured upon replacement. Refer to Module Communications Network (Information Bus).
- The diagnostic tool may display ICM for the instrument cluster.
- For any concerns with the restraint control module (RCM), refer to Air Bag Systems.

The instrument cluster is a hybrid electronic instrument cluster (HEC). The vehicle electronic functions are divided into zones. The instrument cluster, FEM, and REM use the standard corporate protocol (SCP) communication network to transmit and receive information. It is very important to understand:
- where the input (command) originates from
- all information (messages) necessary in order for a feature to operate
- which module(s) receive(s) the input or command message
- does the module which received the input (message), control the output of the feature, or does it output a message over the SCP communication network to another module
- which module controls the output of the feature

The instrument cluster communicates with the FEM, REM, anti-lock brake system/traction control/interactive vehicle dynamics (ABS/TC/IVD), powertrain control module (PCM), steering column lock (SCL), message center (MC) module, and the RCM over the SCP to control the gauges, indicators, and chimes.

Integrated Circuit Display
The integrated circuit display maintains three separate functions housed in a single display area, the warning center display, the trip A/B, and the odometer display.

Warning Center Display
The warning center display is a florescent vacuum tube display that alerts the driver of a lamp outage condition. The FEM and REM both control the exterior illumination. When an exterior lamp(s) is inoperative, the FEM or REM notify the instrument cluster over the SCP communication network and the instrument cluster illuminates the warning center message LAMP OUT. The warning center message will remain on until the condition is corrected. Once the condition is corrected, the warning center will display the trip odometer.

Trip A/B And Odometer Displays
The vehicle speed signal (VSS) from all four wheels is hardwired directly to the ABS/TC. The speed status is then sent to the instrument cluster by the ABS/TC over the SCP communication network to establish a rolling count.

PRNDL Display
The digital transmission range (TR) sensor is hardwired directly to the PCM. The status of the gear selection is sent to the instrument cluster from the PCM over the SCP communication network.

Gauges

Fuel Gauge
The fuel gauge system has a saddle-type fuel tank with two integrated fuel senders: the fuel delivery module and the jet pump module. The fuel delivery module is located in the right side of the fuel tank and the jet pump module is located in the left side of the fuel tank. Fuel level status is sent directly to the REM, which is hardwired to the fuel senders. The REM sends the fuel data to the instrument cluster via the SCP line. Normal operating range of the fuel delivery module is from 16 ± 2 ohms at empty (E) to 155 ± 4 ohms at full (F). Normal operating range of the jet pump module sender is from 19 ± 2 ohms at empty (E) to 160 ± 2 ohms at full (F). If either the REM or jet pump module fuel sender has an open or shorted signal, the instrument cluster will log diagnostic trouble code (DTC) B1201. If the jet pump module sender is open, the fuel gauge will default to the fuel delivery module sender value only and the fuel gauge will indicate E to 1/2 tank (depending on the fuel level on the fuel delivery module side of the tank). If the fuel delivery module is open, the fuel gauge will default to the empty position.

Speedometer Gauge
The instrument cluster uses a vehicle speed signal from the ABS/TC/IVD system to control the movement of the speedometer pointer. Vehicle speed information is sent to the ABS/TC/IVD module from all four wheel speed sensors, which is then sent to the instrument cluster by the ABS/TC/IVD module over the SCP communication network.

Tachometer Gauge
The instrument cluster uses crankshaft speed information, sent to the PCM from the crankshaft position sensor, to control the movement of the tachometer pointer. The crankshaft position sensor is hardwired directly to the PCM, which provides the crankshaft position sensor status to the instrument cluster over the SCP communication network.

Temperature Gauge
The cylinder head temperature sensor is hardwired directly to the PCM. The status of the cylinder head temperature is sent from the PCM over the SCP communication network to the instrument cluster. Normal operating temperature is 60°C (140°F) to 120°C (248°F). Redline starts at 121°C (249.8°F).

Warning Indicator Lamps

Air Bag Warning Indication
The supplemental restraint system is monitored and controlled by the RCM. The status of the supplemental system is sent from the RCM to the instrument cluster through hardwired circuitry. The AIR BAG warning indicator is illuminated if the restraint control module (RCM) sends a ground signal to the instrument cluster.

ABS Warning Indication
The ABS is monitored by the ABS, ABS/TC or ABS/TC/IVD module, which sends the status signal to the instrument cluster over the SCP communication network. The instrument cluster uses this input to determine whether or not there is a fault with the ABS, ABS/TC or ABS/TC/IVD system and turns on the ABS warning indicator according to the input.

Brake Warning Indication
The brake warning indicator supports three separate functions: base brake system failure, low brake fluid level, and engagement of the parking brake. These functions are controlled by the parking brake control switch, the brake fluid level switch and the brake system itself. The brake fluid level switch and the parking brake control switch are hardwired directly to the FEM. The status of both the brake fluid level and parking brake switches are sent from the FEM to the instrument cluster over the SCP communication network. The base brake system status is monitored by the ABS/TC module and sent to the instrument cluster over the SCP communication network.

Charging System Warning Indicator
The charging system controls are accomplished through the PCM, which monitors the output of the generator through hardwired circuitry. The status of the charging system is then relayed from the PCM to the instrument cluster over the SCP communication network.

Door Ajar Warning Indication (Base Cluster Only)
The rear door switches and the decklid ajar switch are directly hardwired to the REM. The door switches for the front of the vehicle are directly hardwired to the FEM. The FEM and REM both use the multiple inputs from the door switches and the decklid ajar switch to determine whether the doors and the decklid ajar switch are in the opened or closed position. The door ajar status is sent to the instrument cluster from both the FEM and REM over the SCP communication network.

Engine Over-Temperature Warning Indicator
The engine over-temperature status is determined by the cylinder head temperature sensor, which is hardwired directly to the PCM. The status of the cylinder head temperature is sent from the PCM over the SCP communication network to the instrument cluster. The instrument cluster then determines whether or not the cylinder head temperature is above the over-temperature threshold.

Low Fuel Warning Indicator (Base Cluster Only)
There are two fuel tank senders, which are hardwired directly to the REM. The status of the fuel level from both senders is sent from the REM over the SCP communication network to the instrument cluster. The instrument cluster uses these inputs to determine the overall fuel level in the tank and illuminates the low fuel warning indicator if the fuel level is low.

Low Washer Fluid Warning Indication (Base Cluster Only)
The low washer fluid level switch is hardwired directly to the FEM. The FEM monitors the washer fluid level status and sends it to the instrument cluster via the SCP communication network.

Safety Belt Warning Indicator
The instrument cluster receives the safety belt warning status from the RCM through hardwired circuitry. The safety belt switch is hardwired to the RCM. When the safety belt is fastened, the safety belt switch opens and removes the ground to the RCM and when the safety belt is unfastened, the safety belt switch closes and grounds the circuit to the RCM.

Indicator Lamps

Advance Traction Indication
The status of the advance traction control system is communicated to the instrument cluster from the ABS/TC/IVD module over the SCP communication network. When the advance traction control system is switched OFF, the ABS/TC/IVD module will send a command to the instrument cluster to illuminate the advance traction indicator.

CHECK FUEL CAP (Base Cluster Only)
The CHECK FUEL CAP indicator is used to indicate significant leaks in the fuel tank evaporative system due to a loose fuel cap. Fuel tank pressure is monitored by the PCM and if a leak is detected it signals a fault to the instrument cluster over the SCP network. Once the PCM has detected a loose fuel cap and the CHECK FUEL CAP indicator is illuminated, the indicator will remain illuminated until the fuel cap is secured and the ignition switch has been cycled one time.

Electronic Throttle Control (Base Cluster Only)
The instrument cluster receives the electronic throttle control status from the PCM over the SCP communication network. When a system concern is detected, the PCM sends the instrument cluster a command signal to turn the electronic throttle control indicator ON.

High Beam Indication
The multifunction switch is hardwired directly to the instrument cluster. The headlamp status is then sent from the instrument cluster to the FEM via the SCP communication network.

Low Oil Pressure Indication
The low oil pressure switch is hardwired to the FEM. The status of the oil pressure is sent from the FEM to the instrument cluster via the SCP communication network.

Malfunction Indicator Lamp (MIL)
After the engine is started, the MIL proves out for a duration of three seconds. If the instrument cluster does not receive a message from the PCM within five seconds, it sends two messages to the PCM and attempt to reestablish communication. If the instrument cluster is unable to reestablish communication, the instrument cluster illuminates the MIL and logs a diagnostic trouble code (DTC).

Speed Control Indication
The speed control status is monitored by the PCM and then relayed to the instrument cluster via the SCP communication network. The speed control indicator illuminates when the speed control is set.

Steering Column Lock Indication
The instrument cluster monitors the key-in-ignition status, ignition switch position status and the steering column lock status. When the key is in the ignition, the key is in the RUN position and the steering column is locked, the instrument cluster turns on the steering column lock warning indicator. The steering column lock status is sent to the instrument cluster from the steering column lock (SCL) module over the SCP communication network.

Traction Control Indication
The status of the traction control is communicated to the instrument cluster from the ABS/TC/IVD module via the SCP communication network. When the traction control system is active, the ABS/TC/IVD module sends a command to the instrument cluster to illuminate the traction control indicator.

Turn/Hazard Indication
The multifunction switch is hardwired directly to the instrument cluster. The instrument cluster sends the signal from the multifunction switch to both the FEM and REM via the SCP communication network while simultaneously illuminating the turn/hazard indicators. The FEM and the REM use these inputs from the instrument cluster to illuminate the exterior lighting as necessary.