Principles of Operation (How Does It Work?)

PRINCIPLES OF OPERATION

The Expedition and Navigator instrument clusters are configurable, hybrid electronic clusters (HEC) that contain a microprocessor, gauges, indicator lamps, and internal circuitry. The instrument cluster is non-repairable at the dealership level with the exception of the warning indicator bulbs on the Expedition only and the instrument cluster lens on both the Expedition and Navigator clusters. The instrument cluster utilizes hardwired circuitry, the standard corporate protocol (SCP), and UART based protocol (UBP) communication networks. Communication using the SCP network transmits and receives data between the instrument cluster, the PCM, and the anti-lock brake system/traction control/integrated vehicle dynamics (ABS/ITC/IVD) module. Communication using the UBP network utilizes data transmitted and received by the instrument cluster and the four-wheel drive control module, power liftgate module (Navigator only), parking aid module, air suspension module, vehicle security module, driver seat module and the electronic air temperature control (EATC).

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 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. When the ignition switch is turned to the ON position with the engine off, the following indicators will illuminate:
- 4x4 HIGH indicator
- 4x4 LOW indicator
- ABS warning indicator
- air bag warning indicator
- BRAKE warning indicator
- oil pressure warning indicator
- coolant temperature warning indicator
- low fuel warning indicator
- HI TEMP/LOW OIL warning indicator
- low washer fluid indicator
- traction control indicator
- CHECK SUSP indicator
- door ajar indicator

Gauge Indication Systems

Instrument Cluster Replacement

CAUTION: When installing a new instrument cluster, the instrument cluster must be re-configured.

When installing a new instrument cluster, contact the Instrument Cluster Program.

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

Speedometer
The instrument cluster receives the vehicle speed sensor (VSS) signal from the powertrain control module (PCM) through the standard corporate protocol (SCP) communication network. The instrument cluster micro-processor monitors the VSS input from the PCM and commands the speedometer with a corresponding movement of the 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 miles in English mode or one million kilometers in metric mode based upon rolling count data sent from the PCM through the SCP network. The trip odometer is resettable and accumulates and registers up to 1,000 miles or 1,000 kilometers.

Fuel Gauge
The instrument cluster is hardwired to the fuel sending unit, which is a variable resistor controlled by the action of a float arm. When the fuel level is low, resistance in the unit is low (15 ohms ± 1 ohm). When the fuel level is high, the resistance is high (160 ohms ± 2 ohms). The instrument cluster micro-processor monitors the input from the fuel sender and commands the fuel gauge indication according to the fuel level data.

Temperature Gauge
The PCM receives the engine coolant temperature status through hardwired circuitry to the engine coolant temperature (ECT) sensor. The instrument cluster receives the engine coolant temperature data from the PCM through the SCP communication network. The instrument cluster microprocessor monitors the engine coolant temperature data received from the PCM and commands the temperature gauge indication with a corresponding movement of the pointer.

Oil Pressure Gauge
The instrument cluster is hardwired to the oil pressure sender unit. The oil pressure sender unit 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 and when sufficient oil pressure exists, the oil pressure switch closes providing a ground signal to the instrument cluster. The instrument cluster microprocessor monitors the oil pressure and commands the oil pressure gauge indication with a corresponding pointer movement.

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

Tachometer
The instrument cluster receives the tachometer data from the PCM through the SCP network and commands the tachometer according to the data.

Warning Indicators

Charging System Warning Indicator
The instrument cluster receives the charging system status from the PCM through the SCP communication network. Charging system data is monitored by the instrument cluster microprocessor and when charging system voltage is low, turns on the charging system indicator by providing a ground.

BRAKE Warning Indicator
The parking brake switch is hardwired to the instrument cluster and the brake fluid level switch is hardwired to the ABS module. The instrument cluster BRAKE warning indicator utilizes two inputs. The first input is provided by the parking brake switch and when applied, provides a ground to the instrument cluster turning on the BRAKE warning indicator. The second input is controlled by the ABS module. The ABS module, upon receipt of a low brake fluid level signal, ABS concern, or base brake system concern, provides a brake signal to the instrument cluster through the SCP communication network. The instrument cluster microprocessor upon receipt of the brake signal, controls the BRAKE warning indicator according to the monitored signal.

ABS Warning Indicator
The ABS warning indicator is used to indicate an ABS concern or deactivation of the ABS. The instrument cluster receives the ABS message from the ABS module through the SCP communication network.

Malfunction Indicator Lamp (MIL)
The malfunction indicator lamp (MIL) is illuminated when a diagnostic trouble code (DTC) is detected by the powertrain control module (PCM). The instrument cluster receives the MIL data from the PCM through the SCP network.

Air Bag Warning Indicator
The instrument cluster is hardwired to the restraint control module. If an air bag system concern is detected, a DTC is logged and the restraint control module provides a ground path to the instrument cluster turning on the air bag indicator.

Safety Belt Warning Indicator
The restraint control module monitors the safety belt position through the safety belt buckle switch. When the safety belt is buckled, the restraint control module receives a ground signal and sends a SCP message to the instrument cluster to turn off the safety belt warning indicator. When the safety belt is unbuckled, the ground to the restraint control module is removed and the restraint control module sends a SCP safety belt warning message to the instrument cluster to turn on the indicator.

Low Fuel Warning Indicator (if equipped)
The low fuel warning indicator is controlled by the instrument cluster microprocessor and utilizes hardwired fuel level data from the fuel pump module. When the fuel level drops below approximately one-sixteenth of a tank, the instrument cluster microprocessor turns on the low fuel warning indicator.

Coolant Temperature Warning Indicator (if equipped)
The PCM receives the engine coolant temperature status through hardwired circuitry from the engine coolant temperature (ECT) sensor. Engine coolant temperature status is subsequently transmitted to the instrument cluster from the PCM through the SCP communication network. The instrument cluster microprocessor monitors the engine coolant temperature data received from the PCM and commands the coolant temperature warning indicator on when coolant temperature reaches 244°-250°F (118°-121°C).

Low Oil Pressure Warning Indicator (if equipped)
The instrument cluster is hardwired to the oil pressure sender unit. The oil pressure sender unit consists of a diaphragm and contact points, which are normally open. When there is low (under 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 microprocessor monitors the oil pressure ground signal and commands the low oil pressure warning indicator on or off according to engine oil pressure.

Door Ajar Indicator
The door ajar switches provide a ground signal to the vehicle security module. The vehicle security module, upon receipt of the door ajar ground data, supplies a door ajar status message to the instrument cluster through the UBP communication network. The instrument cluster microprocessor monitors the door ajar status and commands the door ajar indicator on or off according to the door ajar status message.

Traction Control Indicator - Navigator
The traction control indicator flashes when the vehicle traction control is in active mode or is being controlled by the ABS/TC/IVD module. The instrument cluster receives the traction control signal from the anti-lock brake system/traction control/integrated vehicle dynamics (ABS/TC/IVD) module through the UBP communication network. The instrument cluster monitors the traction control signal and when the ABS/TC/IVD module detects a traction control concern, the instrument cluster microprocessor will turn on the traction control 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.

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.

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

HI TEMP/LOW OIL Warning Indicator - Expedition
The HIGH TEMP/LOW OIL warning indicator will illuminate when either of the following conditions exist:
- if the engine oil pressure drops below approximately 42 kPa (6 psi)
- if the engine temperature exceeds approximately 118°C (244°F)

Low Washer Fluid Indicator - Expedition
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.

CHECK SUSP Indicator - Expedition
The instrument cluster is hardwired to the suspension control module. The CHECK SUSP indicator is powered through the instrument cluster, and when the air suspension is activated, the suspension control module provides the ground to the instrument cluster and illuminates the CHECK SUSP indicator.

Overdrive Off Indicator
The instrument cluster receives the overdrive off signal from the PCM through the SCP communication network. The overdrive off switch is hardwired to the PCM. When the transmission overdrive is selected off, the overdrive off switch provides a ground signal to the PCM. The PCM upon receipt of the overdrive off ground signal, provides an SCP overdrive off signal to the instrument cluster and the instrument cluster microprocessor will turn on the overdrive off indicator.

4x4 HIGH and 4x4 LOW Indicators
The instrument cluster receives the 4x4 HIGH and 4x4 LOW information from the four-wheel drive control module through the UPB communication network. When either 4x4 high or 4x4 low are selected, the four-wheel drive control module will provide a 4x4 status signal to the instrument cluster microprocessor and turn on the appropriate indicator.