Principles of Operation (How Does It Work?)

PRINCIPLES OF OPERATION

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

The instrument cluster (IC) is a hybrid electronic cluster (HEC). The instrument cluster uses both hardwired and the standard corporate protocol (SCP) line to transmit and receive information. It is very important to understand:
- where the input originates from.
- all 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 line network to another module?
- which module controls the output of the feature.

The instrument cluster carries out a display prove-out to verify that all warning/indicator miniature bulbs and monitored systems are functioning correctly. When the ignition switch is in the ON position with the engine off, the following warning indicators will illuminate:
- malfunction indicator lamp (MIL) (SERVICE ENGINE SOON)
- charging system indicator
- low oil pressure warning indicator
- anti-lock brake (ABS) warning indicator
- safety belt warning indicator
- air bag warning indicator
- BRAKE warning indicator
- low fuel indicator
- THEFT indicator
- low coolant warning indicator (3.0L engine)
- O/D OFF indicator

Gauge Indication Systems
The gauge indication systems use air-core gauges mounted in the instrument cluster. No adjustment, calibration, or maintenance is necessary for any of the gauges. The gauges cannot be installed separately.

Instrument Cluster Replacement
When instrument cluster replacement is necessary, contact the Instrument Cluster Replacement Program at 1-800-259-9700.

Speedometer
The instrument cluster receives the vehicle signal from the powertrain control module (PCM) via the SCP line. If the instrument cluster receives no signal the speedometer will default to 0.0 km/h (0.0 mph).

Odometer
The vehicle is equipped with two odometers. The primary odometer shows cumulative distance. The second odometer is the trip and tenths odometer.

Tachometer
The tachometer is electrically operated and indicates engine speed in a range of 0 to 8,000 rpm. The tachometer receives the signal via the SPC line from the PCM. If the rpm information sent to the instrument cluster is invalid or missing the instrument cluster will default the tachometer to 0.0 rpm.

Fuel Gauge
The instrument cluster receives the fuel signal via the hardwired circuitry from the fuel pump module. The fuel pump module changes resistance according to the amount of fuel in the fuel tank and varies the current flow through the fuel gauge. A low resistance will result in a lower gauge indication, while a high resistance will result in a higher gauge indication. The fuel gauge is controlled by the instrument cluster micro processor and varies the position according to data received form the fuel pump module.

Temperature Gauge
The instrument cluster receives the engine coolant temperature signal from the PCM via the SCP line and displays the information on the temperature gauge. If the instrument receives no signal the temperature gauge will default to the COLD position.

Low Oil Pressure Warning Indicator
The low oil pressure warning indicator is hardwired to the oil pressure switch and is identified by an oil can symbol on the instrument cluster. The oil pressure switch is a normally closed switch. When the engine is off or has no oil pressure the switch is closed, providing a gradual path to turn on the light. When the engine is running and there is oil pressure present, the switch is opened and no ground is provided.

Low Coolant Level Warning Indicator - 3.0L (4V) Engine
The low coolant level warning indicator illuminates when the instrument cluster receives a signal that the engine coolant is low. When the vehicle is parked, there is a two second delay before the instrument cluster illuminates the low coolant indicator. When the vehicle is moving, there is a 25 second delay before the instrument cluster illuminates the low coolant indicator.

Charging System Indicator
On the 3.0L (4V) engine, the charging system indicator is hardwired to the generator and illuminates when the generator output is insufficient to maintain the battery state of charge. On 2.0L Zetec engine, the instrument cluster receives its signal from the PCM via the SCP line.

Air Bag Warning Indicator
The air bag warning indicator is hardwired to the restraint control module. When the supplemental restraint system (SRS) is operating correctly, the air bag warning indicator illuminates for approximately six seconds when the ignition switch is turned on. It only illuminates after starting if a malfunction is present in the SRS.

Service Engine Soon Indicator
When the ignition is in the ON position the bulb will prove out. During vehicle operation, the malfunction indicator lamp (MIL) illuminates when the PCM has detected a fault. If a fault is detected the PCM sends a signal to the instrument cluster via the SCP line and turns on the MIL lamp.

High Beam Indicator
The high beam indicator is hardwired to the steering column multifunction switch and illuminates when the headlamps are placed in the high beam position or the flash-to-pass position.

Turn Indicator
The RH or LH turn indicators are hardwired to the steering column multifunction switch and illuminate intermittently relative to the position of the turn signal switch on the steering column.

Brake Warning Indicator
The brake system warning indicator has multiple functions. It illuminates when the parking brake is applied, when the brake fluid level is low or when a fault is detected in the anti-lock brake system (ABS). It utilizes both hardwired circuitry and the instrument cluster micro processor. The bulb prove-out occurs for approximately three seconds after placing the ignition is in the RUN position. The BRAKE warning indicator will go out following prove-out if the brake fluid level is correct and the parking brake is released.

Anti-Lock Brake Warning Indicator (ABS) (if equipped)
The anti-lock brake warning indicator (ABS) illuminates when the anti-lock brake control module detects a fault in the system. If a fault is detected the anti-lock brake control module sends a signal to the instrument cluster via the hardwired circuitry and the instrument cluster illuminates the ABS warning indicator.

Safety Belt Warning Indicator
The safety belt warning indicator illuminates when the driver safety belt is not fastened. The driver safety belt switch (part of the retractor) is hardwired to the instrument cluster and provides the input into the instrument cluster signaling when the safety belt is connected. The instrument cluster then illuminates the bulb depending on the safety belt retractor position.

Theft Indicator
The theft indicator located in the instrument cluster is controlled by the signal sent via the SCP line from the PCM.

4WD Indicator Lamp (if equipped)
The 4WD indicator is hardwired to the 4WD switch. When 4WD is selected the 4WD switch provides voltage to the cluster and illuminates the 4WD indicator.

Speed Control Indicator (if equipped)
The speed control indicator is hardwired to the speed control module and illuminates when the speed control is switched on.

Door Ajar Indicator
The door ajar indicator is hardwired to the generic electronic module (GEM) and will illuminate when any of the doors or the liftgate are opened.

Low Fuel Warning Indicator
The low fuel warning indicator proves out for three seconds when the ignition is placed in the RUN position. The indicator will then remain on if the fuel level is less than approximately three gallons.

O/D OFF indicator (if equipped)
The O/D OFF indicator will illuminate when the transmission overdrive has been turned off. The instrument cluster receives a switch status signal via SCP line from the PCM.

PRND21 Indicator (automatic transaxle only)
The instrument cluster PRND21 indicator is a liquid crystal display (LCD) that displays the transmission range selected. Two sets of input signals are necessary for the PRND21 to operate correctly. The instrument cluster receives the transmission range signal via hardwired circuitry from the transmission range selector and displays the appropriate range in the LCD. The brake shift interlock module provides the second input signal. If the brake shift interlock module input is not present, the P range will not be highlighted in the LCD display.

Check Fuel Cap
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 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 indicator will remain illuminated until the fuel cap is secured and the vehicle has been running for several minutes.