Principles Of Operation

Turn Signal and Hazard Lamps

Principles of Operation

The Body Control Module (BCM) monitors the multifunction switch position by sending voltage signals to the multifunction switch and the Front Controls Interface Module (FCIM). When the multifunction switch is in the LH or RH TURN position, or the hazard flasher lamp switch is pressed, that input signal is routed to ground.

When the BCM (Body Control Module) receives a request for a turn signal or hazard lamp function, the BCM (Body Control Module) supplies on/off voltage to the appropriate turn lamps.

On 4-door vehicles, turn relays interrupt the stoplamp switch output and allow the BCM (Body Control Module) to control voltage to the combination stop/turn lamps.

The timed on/off cycle for the turn lamps is determined by the BCM (Body Control Module) and is set to flash approximately 75 times per minute if both the front and rear turn lamps operate correctly. If an individual turn lamp is inoperative, the BCM (Body Control Module) flashes the remaining turn lamp approximately 150 times per minute.

The timed on/off cycle for the hazard lamp function is set to flash all the turn lamps approximately 75 times per minute.

Field-Effect Transistor (FET) Protection

A Field-Effect Transistor (FET) is a type of transistor that, when used with module software, monitors and controls current flow on module outputs. The FET (Field-Effect Transistor) protection strategy prevents module damage in the event of excessive current flow.

The BCM (Body Control Module) utilizes a FET (Field-Effect Transistor) protective circuit strategy for many of its outputs (such as a turn lamp output circuit). Output loads (current level) are monitored for excessive current (typically short circuits) and are shut down when a fault event is detected. A short circuit DTC sets when the fault event occurs.

The circuit remains off until the fault is corrected and the ignition is cycled off and then back on, the module resets the FET (Field-Effect Transistor) protection and allows the circuit to function.

The FET (Field-Effect Transistor) protected circuits for the turn lamp system are the turn relay coil ground circuits and the front and rear turn lamp voltage supply circuits.