Principles of Operation

PRINCIPLES OF OPERATION

When installing a new instrument cluster, it is necessary to upload the module configuration to the scan tool. Following installation of the new instrument cluster, download the module configuration from the scan tool into the new instrument cluster.Refer to Information Bus (Module Communications Network).

The following items are configurable:
- Overspeed warning
- Belt minder
- 4x4 feature
- Speedometer scaling
- Electronic automatic temperature control (EATC)
- Default language
- Trailer brake controller
- Transit mode
- Tank configuration

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 warning bulbs, and the transmission range selector. 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 uses data transmitted and received between the instrument cluster, the trailer brake control (TBC) electronic control unit, 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, the vehicle security module, and the electronic automatic temperature control (EATC).

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 CAN 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. The safety belt warning indicator proves-out for 65-seconds or until the safety belt is fastened. The malfunction indicator lamp (MIL), and the wait to start indicator (diesel engines) illuminate continuously until the engine is started and operating normally. When the ignition switch is turned to the ON position with the engine off, the following indicators illuminate for 3 seconds:
- LOW RANGE indicator
- 4x4 indicator
- BRAKE warning indicator
- ABS warning indicator
- Charging system warning indicator
- Door ajar indicator
- Air bag warning indicator (6 seconds)
- Electronic throttle control

Integrated Circuit Display
The integrated circuit display is a vacuum fluorescent tube display that contains the odometer, trip odometer on base clusters and the compass display on message center clusters. The compass module is hardwired to the instrument cluster. The odometer information is transmitted from the PCM through the communication network to the instrument cluster. The instrument cluster displays the appropriate message(s) upon receipt of the compass heading and odometer data received.

Gauges

Speedometer
The instrument cluster receives the vehicle speed sensor (VSS) signal from the PCM through the communication network. The instrument cluster monitors the VSS input from the PCM and commands a corresponding movement of the speedometer 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 kilometers in metric mode or one million miles in English mode, based upon rolling count data sent from the PCM over the communication network. The trip odometer is resettable and accumulates and registers up to 9,999 kilometers or 9,999 miles.

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. 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 in the unit is high (160 ohms ± 4 ohms).

NOTE: It is critical to follow the pinpoint test diagnostic methods to make sure the correct mode is being used during diagnostics.

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 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 (automatic transmissions) or when the parking brake is applied (manual transmissions). 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. The key ON fueling 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 during 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.

Engine Coolant Temperature Gauge
The instrument cluster monitors the engine coolant temperature data received from the PCM over the communication network, and commands the temperature gauge indication with a corresponding movement of the pointer. The temperature gauge also indicates when failsafe cooling is active.

Oil Pressure Gauge
The instrument cluster is hardwired to the oil pressure sender unit. The instrument cluster monitors the oil pressure data and commands the oil pressure gauge indication with a corresponding movement of the pointer. The oil pressure indicator sender unit consists of a diaphragm and contact points. When the engine is started, the contact points close, causing the gauge to indicate normal oil pressure. With no oil pressure, the contacts open and the gauge indicates low oil pressure.

Voltage Gauge (Manual Transmission Only)
The voltage gauge displays the system voltage as measured at the instrument cluster RUN input circuit.

Transmission Temperature Gauge (Automatic Transmission Only)
The instrument cluster receives the transmission temperature information from the PCM over the communication network. The instrument cluster monitors the transmission temperature data and commands the gauge indication with a corresponding movement of the pointer.

Tachometer
The tachometer is electrically operated and indicates the engine speed in revolutions per minute (rpm). The tachometer range is 0 to 6,000 rpm (gasoline vehicles) or 0 to 5,000 rpm (diesel engines). 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.

Turbo Boost (Diesel Only)
The PCM sends the instrument cluster a message over the communication network indicating the boost range of the turbocharger.

Warning Indicator Lamps

Air Bag Warning Indicator
The instrument cluster is hardwired to the restraint control module (RCM). If an air bag system concern is detected, a diagnostic trouble code (DTC) is logged, and the RCM 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 communication network, turns on the ABS warning indicator.

BRAKE Warning Indicator
The instrument cluster BRAKE warning indicator illuminates when the parking brake is applied, or when there is a low brake fluid level. 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 when the electrical connector is disconnected.

Charging System Warning Indicator
On vehicles equipped with gasoline engines and diesel engines with a single generator, when the ignition switch contacts are closed, battery current flows through the charging system indicator and the parallel resistor (390 ohms) to the voltage regulator. Internal circuitry in the voltage regulator provides a ground path to the instrument cluster and the indicator illuminates. When the generator builds up enough voltage to energize the voltage regulator, voltage is applied to the ground side of the indicator effectively removing the ground path and turning the indicator off. On diesel engine vehicles equipped with dual generators, when the ignition switch contacts are closed, battery current flows through the charging indicator and the parallel resistor (390 ohms) to the PCM. The PCM provides a ground to the instrument cluster and the charging system warning indicator illuminates. When the generator builds up enough voltage to energize the voltage regulator, voltage is applied to the PCM. The PCM, upon receipt of the generator charging voltage, removes the ground to the instrument cluster and turns off the charging system warning indicator.

Safety Belt Warning Indicator
The safety belt warning indicator is powered through the instrument cluster and is grounded through the safety belt switch. When the safety belt is buckled, the switch opens and the instrument cluster turns off the safety belt warning indicator. When the safety belt is unbuckled, the switch closes and provides a ground to the instrument cluster to illuminate the safety belt warning indicator.

Malfunction Indicator Lamp (MIL)
The instrument cluster receives engine data from the PCM over the communication network. If a DTC is set by the PCM, the MIL illuminates.

Indicator Lamps

High Beam Indicator
The instrument cluster provides a ground for the high beam indicator. When the high beam headlamps 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.

Speed Control Indicator
The instrument cluster receives the speed control signal from the PCM over the communication network. The PCM communicates to the instrument cluster to illuminate the speed control indicator when the speed control is engaged.

Wait to Start Indicator (Diesel Only)
The wait to start signal is transmitted to the instrument cluster over the communication network from the PCM. The wait to start indicator illuminates when the ignition switch is in the ON position with the engine OFF indicating that the glow plugs are heating.

Tow Haul Indicator
The tow haul indicator illuminates when the tow haul button is pressed on the column-mounted transmission range selector lever. When the vehicle is in the tow mode, the indicator is illuminated by a signal from the PCM to inform the operator that the vehicle will not shift into overdrive. When the indicator is illuminated, the vehicle also provides engine braking and early transmission downshifts when braking on downhill grades.

4x4 HIGH/LOW RANGE Indicators
The 4x4 HIGH and LOW RANGE indicators are both hardwired to the instrument cluster from the 4x4 control module when equipped with electronic shift, or from the 4x4 control switch when equipped with manual shift. The instrument cluster provides the 4x4 indicators with power and the 4x4 control module, or 4x4 switch, provides the ground depending on whether 4x4 high or LOW RANGE is selected.

Wrench Indicator
The instrument cluster receives the electronic throttle control (ETC) status from the PCM over the communication network. When a system concern is detected, the PCM sends the instrument cluster a command signal to illuminate the wrench indicator.