Principles of Operation

PRINCIPLES OF OPERATION

The instrument cluster is a hybrid electronic instrument cluster (HEC). The instrument cluster and the smart junction box (SJB) use a combination of hardwired circuitry and the standard corporate protocol (SCP) communication network to transmit and receive information. It is very important to understand:
- where the input originates.
- 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 communication network to another module.
- which module controls the output of the feature.

When installing a new instrument cluster, it is necessary to upload the module configuration to the diagnostic tool. Following installation of the instrument cluster, download the module configuration from the diagnostic tool into the new instrument cluster. The following items are configurable:
- base display
- low tire pressure warning
- brake system level
- safety belt minder
- overspeed warning
- enhanced door ajar warning display
- overhead display
- speedometer
- default language
- oil life
- oil life status and warning

The base and optional instrument clusters both contain gauges, indicator lamps, and warning lamps that are designed to provide the driver with system status and to alert the driver that certain conditions exist in the vehicle. The optional instrument cluster contains the message center and is located in the cluster. Gauges provide information to the driver indicating the status of systems. The systems that use gauges include vehicle speed, fuel level, engine coolant temperature, and engine rpm. Indicator lamps provide information to the driver of conditions that exist in the vehicle. The indicator lamps include the turn signal, low washer fluid level, traction control, and speed control. Warning indicator lamps provide information to the driver of conditions that could potentially alter vehicle performance. Examples of the warning indicators include the ABS, BRAKE, safety belt, air bag, and low oil pressure.

Each time the ignition switch is turned from OFF to ON, the charging system indicator, the low oil pressure indicator and the malfunction indicator lamp (MIL) prove out and remain on until the engine is started. The safety belt warning indicator proves out for 65 seconds, or turns off when the safety belt is buckled. The air bag indicator proves out for approximately 6-8 seconds while the following instrument cluster indicators and warning indicators prove out for approximately 3 seconds:
- ABS warning indicator
- low tire pressure warning indicator
- lamp out (base cluster only)
- door ajar (base cluster only)
- low fuel
- BRAKE system
- TRAC OFF (if equipped)
- TRAC ACTIVE (if equipped)(base cluster only)
- check fuel cap
- transmission malfunction
- low washer fluid level (base cluster only)
- failsafe cooling warning indicator (base cluster only)

Instrument Cluster Gauges

Engine Coolant Temperature Gauge
The temperature gauge displays the engine coolant temperature (ECT), or the cylinder head temperature (CHT), received from the powertrain control module (PCM) via a network message. The temperature gauge also indicates when failsafe cooling is active. It is a "flat response" gauge providing an indication of whether the engine is cold, normal, overheated, or in failsafe cooling mode. The input temperature and corresponding output gauge command are both filtered to smooth out the pointer movement.

Fuel Gauge
The fuel gauge is to display the quantity of the gasoline in the fuel tank without making the slosh of the fuel in the tank apparent to the customer. A variable resistance driven by a float sends a resistance related to fuel height to the SJB via a hardwired input. The fuel level input data is received over the SCP network from the SJB. The instrument cluster receives the fuel level message and uses the data in the message to display the amount of fuel. The displayed fuel level is also transmitted to the engine controller for emissions purposes. A fast fill feature is also implemented where, if the engine is left running and the vehicle is fueled, the fuel gauge updates at the fast rate if the vehicle speed is less than or equal to 0.5 mph (0.8 km/h) continuously for 5 seconds, the transmission is in PARK, and the fuel level exceeds 2.5 gal (9.46 l) from the fuel level recorded when the vehicle stopped.

Speedometer
The instrument cluster receives the vehicle speed sensor (VSS) signal from the ABS module, via the controller area network (CAN) circuits, and monitors the VSS input and commands the speedometer pointer.

Tachometer
The tachometer gauge displays the engine revolution speed accurately and responsively. The input to the instrument cluster is a SCP message from the PCM. The tachometer gauge feature operates only when the ignition switch is in the RUN or START positions.

Instrument Cluster Indicators

Low Tire Warning Indicator
The low tire pressure monitoring system detects a significant loss of inflation in a single wheel by utilizing the anti-lock brake system (ABS) to monitor the wheel speed sensors for small changes in wheel speed, indicating a low tire. Upon initialization, the low tire pressure monitoring system records the relative wheel speeds of the vehicle for future reference. During operation, the system compares the current vehicle wheel speeds to the recorded wheel speeds. If a tire loses air pressure with respect to the other tires, the ABS module will send a signal via the standard corporate protocol (SCP) network to the instrument cluster and illuminate the low tire warning indicator.

Following the correction of a low tire, the system must be re-initialized. Place the ignition switch in the ON position, press the odometer/trip odometer button 2 times until the display reads "TIRE RESET" or "CHECK TIRES AND RESET". Press and hold the odometer/trip odometer button for approximately 3 seconds until the low tire warning indicator flashes 3 times, indicating the system is initializing.

Check Fuel Cap Indicator
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. If a leak is detected, it signals a fault to the instrument cluster via 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 remains illuminated until the fuel cap is secured and the vehicle has been running for several minutes.

TRAC ACTIVE Indicator (if equipped)
The TRAC ACTIVE indicator illuminates during a traction control event if the vehicle is equipped with traction control and the instrument cluster is configured for traction control.

TRAC OFF Indicator (if equipped)
The TRAC OFF indicator illuminates if the traction control is disabled.

Air Bag Warning Indicator
The supplemental restraint system is monitored and controlled by the restraint control module (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 RCM sends a ground signal to the instrument cluster.

ABS Warning Indicator
The ABS is monitored by the ABS 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 and illuminates. The ABS warning indicator according to the input.

BRAKE Warning Indicator
The brake warning indicator supports 3 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 SJB. The status of both the brake fluid level and parking brake switches are sent from the SJB to the instrument cluster over circuits 1309 (RD/YE) and 1305 (DB). The base brake system status is monitored by the ABS 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 (Base Cluster Only)
The door ajar warning indicator feature informs the driver that any of the 4 doors or liftgate is open or not completely closed. The door ajar warning indicator information is delivered from the SJB to the instrument cluster over the SCP network.

Malfunction Indicator Lamp (MIL)
The MIL is illuminated when a diagnostic trouble code (DTC) is detected by the PCM. The instrument cluster receives the MIL data from the PCM via the SCP network.

Low Fuel Level Warning Indicator
The low fuel indicator illuminates when the fuel level gets low. The instrument cluster receives the fuel level information directly from the fuel sender.

Safety Belt Warning Indicator
The instrument cluster receives the safety belt warning status from the RCM over circuits 1083 (LB/BK) and 608 (BK/YE). 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 turns off the indicator. When the safety belt is unfastened, the safety belt switch closes and grounds the circuit to the RCM and the indicator illuminates.

Low Oil Pressure Warning Indicator
The oil pressure switch is hardwired to the instrument cluster. The oil pressure switch unit consists of a diaphragm and contact points, which are normally open. When there is low (under 41 kPa [6 psi]) or no oil pressure, the oil pressure switch remains open, removing the ground to the instrument cluster. When sufficient oil pressure exists, the oil pressure switch closes, providing a ground signal to the instrument cluster. The instrument cluster monitors the oil pressure ground signal and commands the low oil pressure warning indicator on or off according to engine oil pressure.

Check Transmission Warning Indicator
When the transmission is malfunctioning the PCM sends the instrument cluster a message over the SCP communication network and the instrument cluster illuminates the indicator.

Speed Control Indicator
The speed control status is sent by the speed control activator to the instrument cluster via the SCP communication network. The speed control indicator illuminates when the speed control is set.

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.

LH and RH Turn Signal 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.

Lamp Out Indicator (Base Cluster Only)
The lamp out information is delivered from the SJB to the instrument cluster over the SCP network. The purpose of this indicator is to inform the driver that 1 or more of the exterior lamps are inoperative.

Low Washer Fluid Warning Indication (Base Cluster Only)
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.

Failsafe Cooling Warning Indicator (Base Cluster Only)
The failsafe cooling warning indicator informs the driver the engine is overheating due to loss of engine coolant fluid or other cause and the PCM is taking on limp home strategy. The other purpose is to inform the driver the engine cannot be cooled enough with the limp home strategy and the engine is about to be shut down by the PCM. The failsafe cooling indicator information is delivered from the PCM to the instrument cluster over the SCP network.