Principles of Operation (How Does It Work)

NOTE: A new instrument cluster must be reconfigured. REFER to Module Communications Network (Information Bus).

The instrument cluster is a Hybrid Electronic Cluster (HEC). The instrument cluster uses both hardwired circuitry and the Standard Corporate Protocol (SCP) communication network to transmit and receive information.

There are two basic instrument cluster configurations, the base cluster (except SVT) and the instrument cluster and oil pressure and oil temperature configuration (SVT only). The base cluster configuration is available as either a low series or sports series, which is determined by the option level content of the vehicle. The instrument cluster and oil pressure and oil temperature cluster configuration utilizes a base (instrument cluster) cluster similar to the base cluster with the addition of a separately mounted oil pressure and oil temperature cluster. The oil pressure and oil temperature cluster utilizes both common and unique hardwired inputs and the SCP communication network to receive data.

An additional feature of the instrument cluster and oil pressure and oil temperature cluster configuration is the use of an electro-luminescent backlighting strategy. The electro-luminescent backlighting utilizes switched DC to high AC voltage circuitry. The secondary (minor) cluster 12V DC into AC voltage that is variable up to 180V AC through the dimmer switch control.

CAUTION: The SVT instrument cluster utilizes high AC voltage for the electroluminescent backlighting system in both the base (major) and secondary (minor) clusters. Care must be exercised when making measurements to the instrument cluster circuits.

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.
^ does the module which received the input control the output of the feature, or does it output a message over the SCP 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 miniature bulbs for monitored systems are functioning correctly. When the ignition switch is placed in the ON position with the engine off, the following warning indicators will prove out:
^ check transmission indicator
^ low fuel warning indicator
^ brake warning indicator
^ ice warning indicator

The following indicators are also displayed during prove-out but are not controlled by the instrument cluster:
^ Malfunction Indicator Lamp (MIL) indicator
^ charging system warning indicator
^ Anti-lock Brake System (ABS) warning indicator
^ safety belt warning indicator
^ traction control indicator
^ oil pressure indicator
^ air bag warning indicator
^ air bag deactivation warning indicator
^ door ajar warning indicator
^ speed control indicator

Tachometer
Engine speed information is relayed to the instrument cluster from the Powertrain Control Module (PCM) via the Standard Corporate Protocol (SCP) network.

Speedometer
The instrument cluster receives the vehicle speed signal from the PCM over the SCP network and displays it on the speedometer gauge. If the instrument cluster receives no vehicle speed signal the speedometer defaults to 0.0 km/h (0.0 mph).

Fuel Gauge
The instrument cluster receives the fuel level information from the fuel sender unit (part of the fuel pump module). This is a variable resistor which varies the ground supply to the gauge. When the fuel level is low, the resistance is low, when the fuel level is high the resistance is high. If an invalid input signal is received, the fuel gauge will then default to below the empty position. The fuel level input signal is heavily damped to allow for movement of fuel in the tank when the ignition switch is in the ON position.

Temperature Gauge
Engine coolant temperature information is received by the instrument cluster from the PCM over the SCP network. If the engine coolant temperature information is missing or invalid, the temperature gauge will indicate below the cold (C) position.

Oil Pressure Gauge (SVT Only)
There are two inputs required for correct oil pressure gauge operation. The first input to the instrument cluster is through hardwired circuitry to the oil pressure switch. The second input is the engine rpm, which comes from the PCM through the SCP network. When there is low oil pressure, the oil pressure switch opens and the instrument cluster micro-processor commands the oil pressure gauge into the low region of the gauge. When oil pressure is present the oil pressure switch closes, providing a ground to the instrument cluster and the instrument cluster micro-processor commands the oil pressure gauge into the appropriate region. The rpm signal allows the instrument cluster microprocessor to vary the needle position based upon the speed of the vehicle.

Oil Temperature Gauge (SVT Only)
The engine oil temperature signal is transmitted to the instrument cluster from the PCM through the SCP communication network. The instrument cluster micro-processor upon receipt of the oil temperature data, commands the oil temperature gauge indication to the appropriate needle position.

Odometer
The instrument cluster records the total mileage of the vehicle, using information received from the PCM and electronically displaying this information in a LCD display. If this information is not received, the LCD will display all dashes. On the LCD display there is a tripmeter which can be reset by using the reset button.

Traction Control Indicator
The instrument cluster provides a traction control indication to inform the driver when the traction control is active. The traction control signal comes from the ABS module and is hardwired to the instrument cluster. When the traction control is in the active mode the ABS module provides a ground signal to the instrument cluster and the traction control indicator is turned on.

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 and once a leak is detected, the PCM 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 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. REFER to Computers and Control Systems.

Speed Control Indicator
The speed control indicator is hardwired to the speed control module. When the speed control has been engaged the speed control module provides a ground to the instrument cluster to turn on the speed control indicator.

Low Fuel Warning Indicator
Incorporated into the instrument cluster is a low fuel warning indicator which illuminates when the fuel drops to a pre-determined level.

Brake Warning Indicator
The brake warning indicator has multiple functions. The brake warning indicator self-tests the system when the ignition switch is in the engine RUN position by grounding the circuit. The brake warning indicator illuminates if the brake fluid is low or if the parking brake is set. If both the ABS warning indicator and the brake system warning indicators are illuminated, a concern exists in the ABS module.

Safety Belt Indicator
The instrument cluster safety belt indicator illuminates if the driver safety belt is not fastened when the ignition switch is turned to the ON position. The instrument cluster receives the safety belt status hardwired from the Generic Electronic Module (GEM). The safety belt indicator will turn off after 60 seconds from when the engine is started, regardless of the driver safety belt status.

ABS Warning Indicator
The instrument cluster ABS system indicator is hardwired directly to the ABS module. The ABS warning indicator should prove out when the ignition switch is turned to the ON position. An open circuit, a short to battery, or an ABS failure will illuminate the ABS warning indicator.

Malfunction Indicator Lamp (MIL)
The malfunction indicator lamp (MIL) illuminates when a Diagnostic Trouble Code (DTC) is registered in the PCM if the concern affects exhaust emissions.

Powertrain Malfunction Indicator Lamp
The powertrain malfunction indicator lamp illuminates when a DTC is registered in the PCM which does not affect exhaust emissions. This lamp will also Illuminate if the fail-safe cooling strategy is invoked by the PCM.

Engine Oil Pressure Warning Indicator
The engine oil pressure warning indicator is hardwired to the engine oil pressure switch. With the ignition switch in the ON position, the oil pressure indicator illuminates. After the engine is started and the oil pressure builds up, the oil pressure switch opens and switches off the oil pressure warning indicator.

Door Ajar Indicator
The door ajar indicator is controlled by the GEM, the anti-theft alarm door locking module, and the door, liftgate and luggage compartment lid switches. The system operates by supplying a ground when a door or liftgate is opened or not fully closed, which will illuminate the indicator.

Air Bag Warning Indicator
The instrument cluster air bag warning indicator is hardwired to the restraint control module. An open circuit, a short to battery or an air bag restraint system concern will illuminate the air bag warning indicator.

Charge System Warning Indicator
The PCM controls the charging system and the charge system warning indicator. The PCM is therefore responsible for turning the lamp off once the system is running and illuminating it under fault conditions (including stall conditions).

Shift Up Indicator (Base Cluster Only)
The PCM controls the shift up indicator. This indicator informs the driver when to change gear.

High Beam Indicator
The high beam indicator will illuminate when the multifunction switch is in the high beam position by sending a battery signal to the instrument cluster.

Turn/Hazard Indicators
The right and left turn indicators will illuminate when the multifunction switch is in either turn signal position or hazard lamps position by sending a battery signal to the instrument cluster.

Configuration of the Instrument Cluster
New instrument clusters will illuminate all of the warning indicators until the instrument cluster has been configured using the diagnostic tool. REFER to Module Communications Network (Information Bus).