Instrument Cluster / Carrier: Description and Operation

The instrument cluster contains an analog speedometer, tachometer, fuel gauge and engine coolant temperature gauge. The instrument cluster receives information through hardwired circuitry. The prove-out for the brake warning indicator is with the ignition switch in the START position. Each time the ignition switch is turned from OFF to ON, the following instrument cluster warning indicators will prove out:
- CHECK ENGINE
- safety belt
- Anti-lock Brake System (ABS)
- air bag
- CHECK GAGE
- THEFT

Printed Circuit
The instrument cluster printed circuit is a flexible circuit that supplies power and ground to the instrument cluster indicators and gauges. It is constructed of copper foil bonded to a polyester base film (usually referred to as Mylar).

The flexible circuit is mounted to the instrument cluster housing and, due to its location, cannot be easily tested or inspected in the vehicle. The flexible circuit is vulnerable to damage when a probe is used for in-vehicle testing because the probe can pierce the printed circuit or, in some cases, burn the copper conductor.

Since there is no approved procedure for in-vehicle testing of the flexible circuit, the instrument cluster must be removed from the vehicle for visual inspection. If no damage is evident, each circuit should be checked with an ohmmeter. If an open circuit or a short is detected, a new flexible circuit must be installed.

Gauge Indication Systems
The indication systems use magnetic gauges mounted in the instrument cluster. All the gauges are constructed with windings that form coils. Typically one coil is wound at a 90 degree angle to the other two. The coils form a magnetic field which varies in direction according to the resistance of the sender, except the battery voltage gauge, which is connected between two of them. The battery voltage gauge varies in direction according to the battery voltage. A primary magnet, to which a shaft and pointer are attached, rotates to align to this primary field, resulting in pointer position. No instrument voltage regulator is used with this system. There is no adjustment, calibration or maintenance required for any gauges.

Instrument Cluster Gauge Amplifier/Check Gage Module

NOTE:
- The fuel gauge and instrument cluster gauge amplifier must be installed as a set. The fuel gauge and instrument cluster gauge amplifier are calibrated together.
- If the ignition switch is left in the ON position during fueling, slow fuel gauge indication response may result. The ignition switch must be placed in the OFF position during or after refueling for accurate fuel gauge indication.

The instrument cluster gauge amplifier electrically averages the fuel sender readings so the gauge displays the actual fuel level and not the fluctuations due to fuel sloshing. The amplifier also supplies the signal to illuminate the CHECK GAGE indicator to indicate low fuel, high engine coolant temperature, or low engine oil pressure. The gauge amplifier is a small printed circuit board located in a pocket on the back of the instrument cluster. The electrical connections are made with a spring-type connector. There are no provisions for calibration or adjustment. The fuel gauge and the instrument cluster gauge amplifier must be installed as a unit.

Water Temperature Indicator Sender Unit
When the engine temperature is low, the resistance of the water temperature indicator sender unit is high, thus restricting the flow of current through the gauge and moving the pointer only a short distance. As the temperature of the coolant increases, the resistance decreases, allowing more current to flow through the gauge and results in a corresponding movement of the pointer.

Oil Pressure Indicator Switch
The oil pressure switch is installed in the engine block and consists of a diaphragm and contact points. With oil pressure, 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.

Charge Indicator System
The battery voltage gauge measures the voltage potential at the battery.

Vehicle Speed Signal
The vehicle speed signal is generated by the Output Shaft Sensor (OSS) and sent to the PCM. The PCM sends the vehicle speed signal via circuit 679 (GY/BK) to the instrument cluster.

Speedometer
The electronic speedometer receives a speed signal from the 4WABS module.

Odometer
A million-mile tamper-resistant odometer is standard. New speedometers have an odometer that can be reset to indicate correct vehicle mileage.

NOTE: Some state laws require that the odometer in any new speedometer must register the same as on the removed odometer. New speedometers and odometer modules with the mileage preset are available through Ford electronic repair centers.

If the actual vehicle mileage cannot be determined, the repair centers are able to supply odometers set to "0" miles. An odometer mileage sticker is supplied with the new odometer. This sticker must display the estimated vehicle mileage and be affixed to the driver door jamb.

Trip Odometer
The trip odometer indicates how many miles the vehicle has been driven since the last reset.

Tachometer
The tachometer is a 6,000 rpm tachometer. It has four terminals: one labeled B (12 to 14.5 V), one labeled S (EDIS tach signal in), and two labeled G (cylinder selection grounds). The bottom ground (G) terminal is grounded. The top ground (G) terminal is grounded through a 4.32 k ohm resistor in a 6-cylinder engine vehicle and is connected directly to ground for an 8-cylinder engine vehicle.

Fuel Gauge
The fuel gauge receives its 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 present fuel level. If the fuel level is low, the resistance of the fuel level sensor is low. If the fuel level is high, the resistance of the fuel level sensor high. On flex-fuel vehicles, basic fuel level indication is the same as gasoline vehicles, except that the flex-fuel vehicles incorporate the use of a flex-fuel module. The flex-fuel module is a DC-AC-DC interface, used to prevent reactions created by the interaction of DC current with the fuel. The flex-fuel module is part of the fuel pump module and is installed as an assembly.

Warning Indicators

Brake System
The red brake warning light (BRAKE) is used to indicate a low fluid level, brake malfunction or a parking brake that is not fully released. The brake fluid level switch is located in the brake fluid reservoir.

The yellow brake warning indicator is used to indicate a malfunction or deactivation of the. anti-lock brake system (ABS). It illuminates when triggered by the ABS control module and stays illuminated as long as the malfunction remains in the system.

Charging System Warning Indicator
The charge system warning indicator illuminates when there is no generator (GEN) output.

When the ignition switch contacts are closed, battery current flows through the charge indicator and the parallel resistor (390 ohms) to the voltage indicator, and the indicator illuminates.

When the generator builds up enough voltage to energize a circuit in the voltage regulator, the indicator goes out.

CHECK ENGINE Light
The CHECK ENGINE/Malfunction Indicator Lamp (MIL) is illuminated when a Diagnostic Trouble Code (DTC) or malfunction is sensed in the closed loop by the Powertrain Control Module (PCM).

Air Bag
If an air bag system malfunction is detected a DTC is set and the air bag indicator is illuminated.

Safety Belt
The safety belt warning indicator is powered through the GEM module. When the ignition key is turned on, the indicator illuminates for four to eight seconds even if the safety belt is buckled.

Low Fuel
When the fuel level drops to a predetermined level, the CHECK GAGE indicator will illuminate.

Door Ajar
The DOOR AJAR indicator illuminates when any of the vehicle doors are open.

High Beam
The high beam indicator is illuminated when the high beams are on.

Overdrive (O/D) Off
The O/D OFF indicator illuminates when the transmission overdrive is turned off. This dual function indicator will also flash off and on if a transmission malfunction is detected.

Anti-Theft
Once triggered, the anti-theft system flashes the low beam headlamps, the parking lamps, the THEFT indicator and sounds the horns.

Speed Control
The speed control indicator (SPEED CONT) lamp will illuminate when the speed control is engaged.

CHECK FUEL CAP Indicator
The CHECK FUEL CAP indicator is used to indicate critical 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 the PCM provides a ground to the instrument cluster and illuminates the indicator. Once the PCM has detected a loose fuel cap and the indicator is illuminated, the indicator will remain illuminated until the fuel cap is secured and the vehicle has been running for several minutes.

CHECK GAGE
The CHECK GAGE indicator will illuminate if any of the following occur:
- Engine oil pressure drops below approximately 42 kPa (6 psi).
- Fuel level drops below approximately 4-8L (1-2 gal).
- Engine temperature exceeds approximately 121°C (250°F).