Principles of Operation
The Body Control Module (BCM) supplies the switched and control voltage to the horn relay (integrated into the BCM).
The horn switch consists of 2 sets of contacts separated by springs. The lower set is connected to ground and the upper set is connected to the horn signal circuit. When the driver air bag module is pressed, it pushes down on the upper set of contacts, collapsing the springs and allowing the contacts to touch. When the contacts touch, it completes the circuit and provides the ground signal which is routed through the clockspring, Steering Column Control Module (SCCM) and then to the BCM. The BCM then energizes the horn relay sending voltage to the horn, enabling the horn to sound.
The BCM also provides a momentary ground to the horn relay when the anti-theft system is armed, and an alternating on/off ground when the panic button is pressed on the Remote Keyless Entry (RKE) transmitter.
Normal Operation
When the driver air bag module is pressed, the normally open horn switch (part of the steering wheel) is closed and a path to ground is routed through the clockspring and the Steering Column Control Module (SCCM) and the horn relay is energized. The Body Control Module (BCM) supplies the switched and control voltage to the horn relay, which is integrated into the BCM. The horn relay then provides voltage to the horn, enabling the horn to sound.
This pinpoint test is intended to diagnose the following
- Fuse
- Wiring, terminals or connectors
- Horn
- Clockspring
- Steering wheel harness
- Horn switch (part of the steering wheel)
- BCM
- SCCM
When the driver air bag module is pressed, the normally open horn switch (part of the steering wheel) is closed and ground is routed through the clockspring and the Steering Column Control Module (SCCM) to the horn relay, energizing the horn relay. The Body Control Module (BCM) supplies the switched and control voltage to the horn relay, which is integrated into the BCM. The horn relay then provides voltage to the horn, enabling the horn to sound.
This pinpoint test is intended to diagnose the following
- Wiring, terminals or connectors
- Clockspring
- Steering wheel harness
- Horn switches (part of the steering wheel)
- BCM
- SCCM