Horn Switch - Operation

OPERATION

The floating horn switch contacts allow the vehicle operator to actuate the horns by depressing anywhere on the upper surface of the Driver AirBag (DAB) trim cover in the center of the steering wheel. The four sets of horn switch contacts are wired in parallel so they perform as a single switch. One contact from each switch receives source current from the Local Interface Network (LIN) slave node in the right horizontal spoke of the steering wheel. On vehicles without the optional speed control system, the LIN slave node is the LIN module. On vehicles equipped with the optional speed control system, the LIN slave node is integral to the speed control switch pod.

When the DAB trim cover is depressed, the DAB housing compresses the coil springs isolating one or more of the horn switch contacts causing at least one of the four pairs of electrically conductive contacts to close. When the DAB trim cover is released, the coil springs on the switch contacts return the DAB to its at rest position and open the horn switch contacts, which opens the horn switch circuit.

The horn switch circuit provides inputs to the LIN slave node. The LIN slave node continually monitors this input and, when a change of the switch state occurs, will send electronic horn switch status messages over the LIN data bus to the Steering Angle Sensor (SAS). The SAS is both a LIN master node and a Controller Area Network (CAN) gateway. The SAS will relay the electronic horn switch status messages through the gateway and over the CAN data bus to the Body Control Module (BCM) (also known as the Common Body Controller/CBC). The BCM then controls the output to the horn relay within the Power Distribution Center (PDC) accordingly.

The hard wired circuits between components related to the horn switch contacts may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, details of wire harness routing and retention, connector pin out information and location views for the various wire harness connectors, splices and grounds.

However, conventional diagnostic methods will not prove conclusive in the diagnosis of the horn switch contacts or the electronic controls or communication between modules and other devices that provide some features of the horn system. The most reliable, efficient, and accurate means to diagnose the horn switch contacts or the electronic controls and communication related to horn system operation requires the use of a diagnostic scan tool.