Operation

OPERATION

As messages are sent over the CAN bus circuit, the Front Control Module (FCM) reads these messages and controls power to some of the vehicles electrical systems by completing the circuit to ground (low side driver) or completing the circuit to 12 volt (high side driver). The following functions are controlled by the FCM:

- Front turn signals
- Stop, turn signal and tail lamps
- Front and rear hazard warning lamps
- Headlamps
- Fog Lamps
- Daytime running lamps - if equipped
- Horn
- Windshield and liftgate wiper and washer systems
- Transfer case shifting
- Trailer tow wiring output
- Rear window defroster power and timing
- Air conditioning condenser cooling fan

The FCM provides the following features for the above function:

- It provides a illuminated approach feature that turns the headlamps on when the vehicle is unlocked with the Remote Keyless Entry (RKE) transmitter.
- It flashes lamps in response to turn signal, RKE and Vehicle Theft Security System (VTSS) inputs.
- It sounds the horn in response to RKE and VTSS inputs.
- It turns off the horn in the event of excessively long operation that could otherwise damage the horn.
- It turns off the windshield washer motor after 10 seconds of continuous operation to protect the motor.
- It minimizes voltage variations to the headlamps to extend bulb life and to equalize the light output from the lamps, which might otherwise differ due to variations in wiring resistance.
- If the headlamps are left on, it automatically turns them off after eight minutes to protect the battery from discharge. It monitors battery voltage and turns off non-essential functions such as the fog lamps, rear window defogger, and heated seats if necessary to conserve battery power.
- It operates the high-beam headlamps at reduced intensity by pulse-width modulation of the power supply to provide the daytime running lamps.
- It provides the variable delay intermittent windshield and liftgate wiper time delay features, and the vehicle speed sensitive windshield wiper delay variation.
- It acts as a link between the CAN bus network for critical powertrain and anti-lock brake systems and the network for body and interior modules.