Relay Controls

Fog Lamp Relay

The fog lamp switch is a direct input to the BCM. The BCM sends a PCI Bus message to the FCM informing it to turn on the fog lamp relay. The fog lamp relay is then powered through low side control on pin No. 33 of the FCM. This circuit is electronically controlled and continuously monitored for malfunctions. Fog lamp functionality is not equipped on all vehicles. The FCM "learns" that the vehicle is equipped with fog lamps by reading the BCM PCI Bus message.

Park Lamp Relay

The park lamp switch is a direct input to the BCM. The BCM sends a PCI Bus message to the FCM informing it to turn on the park lamp relay. The park lamp relay is then powered through low side control on pin No. 13 of the FCM. This circuit is electronically controlled and continuously monitored for malfunctions.

Front Wiper On Relay

The front wiper switch is a direct input to the BCM. The BCM sends a PCI Bus message to the FCM informing it to turn on the front wiper on relay. The front wiper on relay is then powered through low side control on pin No. 14 of the FCM. This circuit is electronically controlled and continuously monitored for malfunctions.

Front Wiper High/Low Relay

The front wiper switch is a direct input to the BCM. The BCM sends a PCI Bus message to the FCM informing it to turn on the front wiper high/low relay. The relay switches power between the low speed and high speed windings of the wiper motor. The front wiper high/low relay is powered through low side control on pin No. 34 of the FCM. This circuit is electronically controlled and continuously monitored for malfunctions.

Accessory Relay

The accessory relay works in conjunction with the FCM's power accessory delay feature to control the operation of the radio, power windows, washer motors, wiper motors and power outlet. The accessory relay is turned on through low side control on pin No. 35 of the FCM. This circuit is electronically controlled and continuously monitored for malfunctions. Depending on the ignition switch position, the accessory relay will remain on or will time-out and turn off. The accessory relay remains on in the RUN and ACCY positions of the ignition switch. In the UNLK and OFF positions, the relay will remain energized for 45 seconds then turn off. During this time-out period, if the driver or passenger doors are opened, the relay will turn off immediately. While the ignition switch is in the START position, the relay will also drop-out, then resume operation. Accessory relay operation is most noticeable by observing the operation of the radio or blower functions.

Horn Relay

The horn relay operates through a direct wire input to the FCM from the horn switch (FCM pin No. 17), or a PCI Bus message from the BCM. The relay responds to the horn switch, remote door lock and VTA alarm functions. The horn relay is powered through low side control on pin No. 10 of the FCM. Under normal operating conditions, if the horn is pressed for longer than 30 seconds, the FCM will automatically deactivate the horn to prevent damage to it. The FCM will reactivate control of the relay after a 25 second cool-down period. This circuit is electronically controlled and continuously monitored for malfunctions.

Front & Rear Blower Relay

The blower control switch is part of the Automatic Temperature Control (ATC) or A/C-Heater Control Module, (Manual Temp). When the blower switch is turned on, the ATC or A/C-Heater Control Module sends a PCI Bus message to the FCM. The front and rear blower relay is then powered through low side control on pin No. 30 of the FCM. The relay provides the high side to the blower motor, and the blower speed is governed through low side control in the ATC or A/C-Heater Control Module. This circuit is electronically controlled and continuously monitored for malfunctions.

Name Brand Speakers (NBS) Relay

The NBS relay operates through the vehicle bus interface between the radio and the FCM. When the radio is turned on, the radio sends a PCI Bus message to the FCM. The NBS relay is then powered on through low side control on pin 11 of the FCM. The relay supplies power to the amplified speaker, and ground is supplied through the radio. This circuit is electronically controlled and continuously monitored for malfunctions.

Electronic Back Light (EBL) Relay

The rear defrost switch is part of the Automatic Temperature Control or A/C-Heater Control Module (Manual Temp). When the ignition switch is in the RUN position and the rear defrost switch is turned on, the ATC or A/C-Heater Control Module sends a PCI Bus message to the FCM. The EBL run only relay is then powered through low side control on pin No. 31 of the FCM. The relay provides the high side to the rear window defrost grid, and ground is attached to the vehicle body. The FCM will only allow the rear defrost to operate in the RUN position. This circuit is electronically controlled and continuously monitored for malfunctions.