Horns System Description and Operation. GMC Truck Sierra

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 2007 🢒 Sierra - 4WD 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 Horns System Description and Operation

System Description

The horn system consists of the following components:

•	Body control module (BCM)

•	HDLMP WASH fuse 20 A (VD1/UHT)

•	Horn assembly

•	HORN fuse 15 A

•	Horn PCB relay

•	Horn switch

•	Removable horn relay (VD1/UHT)

System Operation

The vehicle horn system is activated under the following conditions:

•	The horn switch is depressed.

•	The body control module (BCM) commands the horns on. The BCM commands the horns on under any of the following conditions:

-	When the panic button is depressed on the remote control door lock transmitter. For further information refer to Keyless Entry System Description and Operation .

-	When the keyless entry system is used to lock the vehicle, a horn chirp may sound to notify the driver that the vehicle has been locked. The notification feature may be enabled or disabled through personalization. For further information refer to Keyless Entry System Description and Operation .

Circuit Operation w/o VD1 or UHT

Battery positive voltage is applied at all times to the horn relay coil and the horn relay switche. Pressing the horn switch applies ground through the switch contact and the horn relay control circuit to the coil side of the relay, energizing the relay. Battery voltage is then applied through the switch side of the relay through the horn control circuit to the horns. The body control module (BCM) may also apply ground to the horn relay control circuit as described above. The horns sound as long as ground is applied to the horn relay control circuit.

Circuit Operation with VD1 or UHT

The VD1 and UHT vehicles have 2 horn relays. One PCB relay integrated into the underhood fuse block and another removable relay mounted in the engine compartment. Battery positive voltage is applied at all times to both horn relay coils and the horn relay switches. Pressing the horn switch applies ground through the switch contacts and the horn relay control circuits to the coil side of the relays, energizing the relays. Battery voltage is then applied through the switch side of the relays through the horn control circuits to the horns. The body control module (BCM) may also apply ground to the horn relay control circuit as described above. The horns sound as long as ground is applied to the horn relay control circuit.