Principles of Operation (How Does It Work)

Speedometer-Odometer
On vehicle equipped with gasoline engines, the speedometer/odometer is hardwired to the powertrain control module (PCM). The vehicle speed signal is transmitted directly from the PCM to the speedometer/odometer. The PCM receives its signal from the output shaft speed sensor (OSS).

On vehicle equipped with diesel engines, the speedometer/odometer is hardwired to the vehicle speed sensor (VSS).

Safety Belt Warning Indicator
The safety belt warning indicator receives its ground from the warning chime module. When the driver safety belt is buckled it provides the ground for the warning chime module. The safety belt warning indicator prove out is in the RUN position and is controlled by the warning chime module.

Brake Warning Indicator
The brake warning indicator receives its ground signals from the following sources:
^ the parking brake switch provides a ground when the parking brake is depressed
^ the dual brake warning switch provides a ground when there is low brake pressure
^ the Anti-lock Brake System (ABS) control module provides a ground when it senses an ABS system malfunction.
^ the low vacuum switch senses low engine vacuum and provides a ground

The ignition switch provides the brake warning indicator prove out by supplying a ground when it is in the START position.

Anti-lock Brake System (ABS) Warning Indicator
The ABS warning indicator receives its ground from the ABS module when a malfunction is detected in the ABS system. The ABS warning indicator prove out is in the RUN position and is controlled by the ABS module.

SERVICE ENGINE SOON Warning indicator
The SERVICE ENGINE SOON warning indicator receives its ground from the Electronic Engine Control (EEC) module. The SERVICE ENGINE SOON warning indicator prove out flashes in the RUN position and is controlled by the EEC.

Air Bag Warning Indicator
The air bag warning indicator receives a ground from the Electronic Crash Sensor (ECS) module when a system malfunction or deployment has occurred. The air warning indicator prove out is in the RUN position and is controlled by the ECS module.

WAIT TO START INDICATOR (Diesel Only)
The Powertrain Control Module (PCM) provides the ground for the WAIT TO START indicator. The glow plugs and the WAIT TO START indicator operate at the same time. The light illuminates until the PCM has provided time for the glow plugs to heat the chamber. The PCM then opens the indicator ground circuit, turning off the indicator lamp. The WAIT TO START indicator prove out is in the RUN position and is controlled by the PCM.

WATER IN FUEL Indicator (Diesel Only)
The WATER IN FUEL indicator receives a ground signal when water is sensed in the fuel. The fuel tank sender unit grounds the PCM and the PCM then grounds the indicator lamp, turning on the indicator. The WATER IN FUEL indicator prove out is in the RUN position and is controlled by the PCM.

Speed Control Indicator
The speed control indicator is hardwired to the speed control module on gasoline equipped vehicles and to the PCM on diesel equipped vehicles. When the speed control is engaged, the speed control module or PCM provides a ground path to the cluster and turns on the speed control indicator.