Principles of Operation

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 and indicator bulbs. The instrument cluster uses hardwired circuitry, the controller area network (CAN) and the universal asynchronous receiver transmitter (UART)-based protocol (UBP) communication networks. Communication using the CAN transmits and receives data between the instrument cluster and the powertrain control module (PCM), and the anti-lock brake system (ABS) module. Communication using the UBP network uses data transmitted and received by the instrument cluster, and the electronic automatic temperature control (EATC), vehicle security module (VSM), and the driver seat module. The restraints control module (RCM) and the parking aid module communication is on the international standards organization (ISO) network. When installing a new instrument cluster, the instrument cluster must be configured.

The following items must be configured when installing a new instrument cluster:
- Body and security module
- Overspeed warning
- Outside air temperature and compass
- Automatic temperature control type
- Outside air units
- Belt minder
- Speedometer scaling
- Flex fuel (luxury message center cluster)
- Autolamp delay timer (luxury message center cluster)
- Autolocks (luxury message center cluster)
- Transit mode
- Fuel tank size (luxury message center cluster)

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 communication 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 ignition switch is turned to the ON position, the charging system warning indicator and the malfunction indicator lamp (MIL) illuminate until the engine starts and is running normally. The safety belt warning indicator proves out for 6 seconds or until the safety belt is fastened. The door ajar warning indicator illuminates only with the key in the START/RUN position and one or more doors are open, turning off only when the doors are closed. When the ignition switch is turned to the ON position with the engine off, the following indicators illuminate for approximately 3 seconds with the exception of the air bag warning indicator, which illuminates for approximately 6 seconds:
- ABS warning indicator
- BRAKE warning indicator
- 4x4 high indicator
- LOW RANGE indicator
- Electronic throttle control (ETC)
- Traction control indicator

Integrated Circuit Display
The driver information messages are transmitted to the instrument cluster over the communication network. The compass module and outside air temperature sensor are hardwired to the instrument cluster. The odometer and trip odometer information is transmitted from the PCM through the communication network to the instrument cluster.

NOTE: On vehicles equipped with electronic automatic temperature control (EATC), the climate control assembly displays the outside air temperature. The instrument cluster only displays the outside air temperature on vehicles that are not equipped with EATC.

In addition to the compass, outside air temperature and odometer/trip odometer, the integrated circuit provides the driver with information using a text-based format. The CHECK GAUGES display illuminates when there is low oil pressure, high engine coolant temperature or when the vehicle has entered into the fail-safe cooling mode.

Gauges

Speedometer
The instrument cluster receives the vehicle speed sensor (VSS) signal which originates in the ABS module and is transmitted to the PCM over the communication network. The PCM monitors the VSS input and sends it to the instrument cluster over the communication network. With the VSS input, the instrument cluster provides the speedometer with a corresponding pointer movement.

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

Odometer/Trip 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 999,999 kilometers or miles, based upon rolling count data sent from the PCM over the communication network. The trip odometer accumulates and registers up to 999.9 kilometers or miles and can be reset.

Fuel Gauge
The instrument cluster receives the fuel level 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. For vehicles equipped with flex-fuel, when the fuel level is low, resistance in the unit is low (7 ohms ± 2 ohms). When the fuel level is high, the resistance is high (138 ohms ± 4 ohms). For vehicles not equipped with flex-fuel, when the fuel level is low, the resistance in the unit is low (15 ohms ± 2 ohms). When the fuel level is high, the resistance is high (160 ohms ± 4 ohms).

The instrument cluster uses 4 different operating modes to calculate the fuel level:
- Anti-slosh (default mode)
- Key OFF fueling
- Key ON fueling
- Recovery

After a fuel fill up, the time for the fuel gauge to move from empty (E) to full (F) ranges from 2 seconds to 55 minutes depending on which operating mode the fuel gauge is in.

The default fuel gauge mode is called the anti-slosh mode. To prevent fuel gauge changes from fuel slosh (gauge instability due to changes in fuel sender readings caused by fuel moving around in the tank), the fuel gauge takes approximately 55 minutes to go from empty (E) to full (F).

The key OFF fueling mode (2 seconds to read empty [E] to full [F]) requires 3 conditions be met:
- The key must be in the OFF position throughout the entire refueling of the vehicle.
- At least 15% of the vehicle's fuel capacity must be added to the fuel tank.
- The instrument cluster must receive a valid key ON fuel sender reading within 1 second of the key being put into the RUN position. The key ON sample readings are considered valid if the fuel sender reading is between 15 ohms ± 2 ohms and 160 ohms ± 4 ohms.

If these conditions are not met, the fuel gauge stays in the anti-slosh mode, which results in a slow to read full (F) event.

The key ON fueling mode (approximately 90 seconds to read empty [E] to full [F]) requires 3 conditions be met:
- The transmission is in PARK (P) (automatic transmissions), or the parking brake is applied (manual transmissions).
- The key is in the RUN position.
- At least 15% of the vehicle's fuel capacity must be added to the fuel tank.

In key ON fueling mode, a 30-second timer activates after the transmission is put into the PARK (P) position or when the parking brake is applied. When the 30 second time has elapsed and at least 15% of the vehicle's fuel capacity has been added, the fuel gauge response time is 90 seconds to read from empty (E) to full (F). When the transmission is shifted out of PARK (P) or the parking brake is released, the fuel gauge strategy reverts to the anti-slosh mode. This mode prevents slow to read full events from happening if the customer refuels the vehicle with the key in the RUN position.

Recovery mode is incorporated into the instrument cluster strategy to recover from a missing fuel level input after a refueling event. Missing fuel level inputs result from intermittent opens in the fuel sender or its circuits. Recovery mode (empty [E] to full [F] approximately 20 minutes) is initiated when the following 2 conditions are met:
- The instrument cluster is in the anti-slosh (default) mode.
- The actual fuel level in the tank is greater than what is being displayed by the fuel gauge.

Temperature Gauge
The PCM receives the engine coolant temperature status through hardwired circuitry to the cylinder head temperature (CHT) sensor. The instrument cluster receives the engine coolant temperature data from the PCM over the communication network. The instrument cluster monitors the engine coolant temperature data received from the PCM and provides the temperature gauge indication with a corresponding movement of the pointer. If the instrument cluster receives no signal the temperature gauge defaults to the COLD position.

Oil Pressure Gauge
The instrument cluster is hardwired to the oil pressure switch. The oil pressure switch consists of a diaphragm and contact points, which are normally open. When there is low or no oil pressure, the oil pressure switch remains open and removes 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 and provides the oil pressure gauge indication with a corresponding pointer movement.

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

Warning Indicators

Air Bag Warning Indicator
The air bag warning indicator is used to provide a status of the supplemental restraint system. The instrument cluster is hardwired to the RCM. If an air bag system concern is detected, a DTC is logged and the RCM provides a ground path to the instrument cluster turning on the air bag warning 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 communication network, turns on the ABS warning indicator.

BRAKE Warning Indicator
The instrument cluster BRAKE warning indicator illuminates when:
- the parking brake is applied.
- there is low brake fluid level.
- the brake fluid level switch is disconnected.
- an electronic brake distribution (EBD) concern exists.
- a loss of communication between the ABS module and the instrument cluster occurs.

The parking brake switch and the brake fluid level switch are hardwired to the instrument cluster. The parking brake switch provides a ground to the instrument cluster when the parking brake switch is applied. The brake fluid level switch provides a ground to the instrument cluster when the brake fluid level is low or an open circuit or if the switch is disconnected. The base brake system and the EBD system are monitored by the ABS module. When a concern exists with the base brake system or EBD, the ABS module provides a signal to the instrument cluster through the communication network. The instrument cluster turns the BRAKE warning indicator on or off, according to the monitored data.

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

Door Ajar Warning Indicator
The door ajar switches provide a ground signal to the instrument cluster on vehicles not equipped with the remote keyless entry (RKE) system and to the VSM on vehicles equipped with the RKE system. The VSM, upon receipt of the door ajar ground data, supplies a door ajar status message to the instrument cluster through the communication network. The instrument cluster monitors the door ajar status and commands the door ajar warning indicator on or off according to the door ajar status message.

Safety Belt Warning Indicator
The RCM monitors the safety belt position through the safety belt switch (part of the buckle). The RCM communicates the status of the safety belt switch to the instrument cluster through hardwired circuitry. When the safety belt is unbuckled, the safety belt switch closes to ground, signaling the RCM that the safety belt is unbuckled. The RCM provides a ground signal to the instrument cluster to turn on the safety belt warning indicator. When the safety belt is buckled, the safety belt switch opens to the RCM and the RCM in turn removes the ground to the instrument cluster to turn off the safety belt warning indicator.

Tire Pressure Monitoring System (TPMS) Warning Indicator
The instrument cluster receives the TPMS messages from the VSM over the communication network. If the VSM determines that the tire pressure has exceeded the limits, a message is sent to the instrument cluster to turn on the TPMS warning indicator. If a TPMS fault condition exists, the VSM sends a message to the instrument cluster to flash the TPMS warning indicator.

Indicator Lamps

Wrench Warning Indicator
The PCM monitors the electronic throttle control and provides the instrument cluster with the ETC status over the communication network. When a system concern is detected, the PCM provides the instrument cluster with a signal commanding the instrument cluster to turn on the wrench warning indicator.

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.

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.

Malfunction Indicator Lamp (MIL)
The MIL is illuminated when a DTC is detected by the PCM. The instrument cluster receives the MIL data from the PCM through the communication network.

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

4x4 HIGH and 4x4 LOW Indicators
The instrument cluster receives the 4x4 HIGH and 4x4 LOW information from the PCM through the communication network. When either 4x4 high or 4x4 low are selected, the PCM provides a 4x4 status signal to the instrument cluster to turn on the appropriate indicator.

Traction Control Indicator
The instrument cluster receives the traction control signal from the ABS module through the communication network. The instrument cluster monitors the traction control message and when the ABS module detects a traction control concern, the instrument cluster illuminates the traction control indicator. The instrument cluster also flashes the traction control indicator when the vehicle traction control is in active mode.

O/D OFF Indicator
The overdrive (O/D) off function is controlled by the O/D off switch located on the shifter assembly. When the transmission is placed in the O/D off position, the O/D off switch provides voltage to the PCM. The O/D off status is then transmitted to the instrument cluster from the PCM over the communication network.