Horn System - Service Information: Overview Dodge Dart PF

DESCRIPTION

An electrically-operated dual-note horn system is standard factory-installed equipment in this vehicle. Depressing the upper surface of the Driver Air Bag (DAB) trim cover in the center of the steering wheel actuates the horn switch, which provides the vehicle operator with a convenient, audible signaling device that can be used to alert pedestrians or the operators of other vehicles in near proximity.

The horn system features one low-note horn unit and one high-note horn unit. The Body Control Module (BCM) serves as the controller for the horn system, which enables the system to also provide audible outputs to support other vehicle features such as the horn chirp verification of the optional Remote Keyless Entry (RKE) and Remote Start systems as well as the pulsing horn deterrents of the optional Vehicle Theft Alarm (VTA) and the RKE Panic mode.

The horn system includes the following major components, which are described in further detail elsewhere in this service information

1. Horn Switch Plate - The floating horn switch plate is secured to the back of the DAB within the steering wheel hub cavity and also serves as the mounting bracket between the DAB and the steering wheel.
2. Horns - The low note and high note electromagnetic diaphragm-type trumpet horns are each secured by a mounting bracket to the forward-facing outboard ends of the upper radiator cross member.

Certain functions and features of the horn system rely upon resources shared with other electronic modules in the vehicle over a Local Interface Network (LIN) data bus as well as over the Controller Area Network (CAN) data bus. Other electronic modules in the vehicle that may affect horn system operation are

1. Body Control Module - The Body Control Module (BCM) is concealed within the instrument panel to the left of the steering column and communicates over the CAN data bus. Refer to «MODULE, BODY CONTROL, DESCRIPTION»(ref-646224-S31141207742014072800000) .
2. Local Interface Network Module - A LIN module is used only on vehicles that are not equipped with the optional speed control system. The LIN module is a LIN slave node that is concealed beneath the bezel on the right horizontal spoke of the steering wheel. Refer to «MODULE, LOCAL INTERFACE NETWORK, DESCRIPTION»(ref-646224-S05074530802014072800000) .
3. Radio Frequency Hub Module - The Radio Frequency Hub Module (RFHM) (also known as the RF Hub) is concealed on the underside of the package shelf behind the rear seat. It serves as the RF receiver for the Remote Keyless Entry (RKE) or FOB with Integrated Key (FOBIK) transmitters and communicates over the CAN data bus. Refer to «MODULE, RADIO FREQUENCY (RF HUB), DESCRIPTION»(ref-646224-S30712734272014072800000) .
4. Speed Control Switch Pod - The speed control switch pod is used only on vehicles equipped with the optional speed control system. This switch pod includes an integral LIN slave node and is secured to the right horizontal spoke bezel of the steering wheel. Refer to «SWITCH, SPEED CONTROL, DESCRIPTION»(ref-646241-S03171217022014072800000) .
5. Steering Control Module - The Steering Control Module (SCM) is an electronic circuit board which, along with the multifunction switch, is integral and internal to the Steering Column Control Module (SCCM) mounting housing. The SCM is a LIN master node and a gateway for the CAN data bus. The SCCM mounting housing is concealed beneath the steering column shrouds at the top of the steering column, directly beneath the steering wheel. Refer to «MODULE, STEERING COLUMN, DESCRIPTION»(ref-646224-S15426219732014072800000) .

The SCM and the BCM each contain a microprocessor and programming that allow them to communicate with each other and other electronic modules in the vehicle using the Controller Area Network (CAN) data bus. In addition the LIN module, the speed control switch pod and the SCM communicate with each other using a Local Interface Network data bus. Refer to COMMUNICATION, DESCRIPTION .

Hard wired circuitry connects the various horn system components to each other through the electrical system of the vehicle. These hard wired circuits are integral to several wire harnesses, which are routed throughout the vehicle and retained by many different methods. These circuits may be connected to each other and to the vehicle electrical system through the use of a combination of soldered splices, splice block connectors and many different types of wire harness terminal connectors and insulators. Refer to the appropriate wiring information. The wiring information includes wiring diagrams, proper wire and connector repair procedures, further details on wire harness routing and retention as well as pin out and location views for the various wire harness connectors, splices and grounds.

OPERATION

The horn system operates on battery current received from an output of the Body Control Module (BCM) through a relay soldered onto the power circuit board of the BCM. The BCM controls the relay based upon internal programming as well as electronic message inputs received from the Steering Control Module (SCM) over the Controller Area Network (CAN) data bus. The horn system circuit is designed so that the system will remain operational, regardless of the status of the ignition switch.

The vehicle operator can control typical horn system signaling through the horn switch within the hub of the steering wheel. When the upper surface of the Driver AirBag (DAB) trim cover is depressed, it provides a hard wired analog input to the Local Interface Network (LIN) slave node integral to the LIN module or the speed control switch pod in the right horizontal spoke of the steering wheel. The LIN slave node then sends an electronic horn switch status message to the LIN master node integral to the SCM. Then the SCM, which is also a gateway to the CAN data bus, relays an electronic horn request message to the BCM over the CAN data bus.

In addition, the Radio Frequency Hub Module (RFHM) (also known as the RF Hub) send electronic horn request messages to the BCM over the CAN data bus in response to inputs received from the Remote Keyless Entry (RKE) transmitter in vehicles without the optional Passive Entry Keyless Go (PEKG) system, or received from the FOB with Integrated Key (FOBIK) transmitter in vehicles with the PEKG system. Lastly, as the Vehicle Theft Security System (VTSS) controller, the BCM can activate the horn system based upon programming and both hard wired and electronic message inputs from the various VTSS components.

The horns can be activated by the BCM to support each of the following features

1. Remote Keyless Entry System - Remote Keyless Entry (RKE) system Panic mode audible alert.
2. Remote Keyless Entry System - Remote Keyless Entry (RKE) system Lock request audible verification.
3. Remote Start System - Remote Start System Start request audible verification.
4. Vehicle Theft Alarm - Vehicle Theft Alarm (VTA) audible alarm.

The RKE system Lock request audible verification is a customer programmable feature, which allows the feature to be enabled or disabled to suit individual preferences. Refer to CENTER, ELECTRONIC VEHICLE INFORMATION, OPERATION .

The hard wired circuits between components related to the horn system 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 system or the electronic controls and 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 system or the electronic controls and communication related to horn system operation requires the use of a diagnostic scan tool. Refer to DIAGNOSIS AND TESTING and DIAGNOSIS AND TESTING .

Each horn has a path to ground at all times through its wire harness connection to an eyelet terminal secured to the body sheet metal. The horns are completely controlled by a fused B(+) output received through a relay soldered onto the power Printed Circuit Board (PCB) within and controlled by the Body Control Module (BCM).

Within the two halves of the horn housing are a flexible diaphragm, a plunger, an electromagnetic coil and a set of contact points. The diaphragm is secured in suspension around its perimeter by the mating surfaces of the horn housing. The plunger is secured to the center of the diaphragm and extends into the center of the electromagnetic coil. The contact points control the current flow through the windings of the electromagnetic coil.

When the horn is energized, electrical current flows through the closed contact points to the electromagnetic coil. The resulting electromagnetic field draws the plunger and diaphragm toward it until that movement mechanically opens the contact points. When the contact points open, the electromagnetic field collapses allowing the plunger and diaphragm to return to their relaxed positions and closing the contact points again. This cycle continues repeating at a very rapid rate producing the vibration and movement of air that creates the sound that is directed through the horn trumpet outlet.

The horns as well as the hard wired input circuits for the horns may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information.

The horn relay is a electromechanical device that consists of an electromagnetic coil, a resistor and a pair of normally open electrical contacts. One of the two electrical contacts is fixed, while the other contact is movable. The movable relay contact is held away from the fixed contact by spring pressure. The horn relay for this vehicle is soldered in place on the Printed Circuit Board (PCB) internal to the Body Control Module (BCM), which is located within the instrument panel outboard of the steering column.

The horn relay cannot be repaired or adjusted and, if ineffective or damaged, the entire BCM unit must be replaced.

The horn relay within the Body Control Module (BCM) switches battery current to the horns when the BCM energizes the electromagnetic coil of the relay. When the electromagnetic relay coil is energized, it draws and holds the normally open movable contact of the relay against the fixed relay contact. The closed relay contacts supply fused battery current from the BCM to energize the horns.

When the BCM de-energizes the electromagnetic relay coil, spring pressure returns the movable contact to the normally open position, which de-energizes the horns. The resistor within the relay is connected in parallel with the electromagnetic coil, and helps to dissipate voltage spikes that are produced when the coil is de-energized.

The hard wired output of the horn relay within the BCM may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the BCM or the electronic controls and communication between modules and other devices that provide some features of the BCM controlled horn relay. The most reliable, efficient and accurate means to diagnose the BCM or the electronic controls and communication related to BCM controlled horn relay operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.

The floating horn switch plate allows 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 three 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 the floating horn switch plate causing at least one of the three sets of electrically conductive horn switch contacts to close. When the DAB trim cover is released, the coil springs on the switch plate 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 Control Module (SCM). The SCM is both a LIN master node and a Controller Area Network (CAN) gateway. The SCM will relay the electronic horn switch status messages through the gateway and over the CAN data bus to the Body Control Module (BCM). The BCM then controls the output to the horns accordingly.

The hard wired circuits between components related to the horn switch plate 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 plate or the electronic controls and 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 plate or the electronic controls and communication related to horn system operation requires the use of a diagnostic scan tool. Refer to DIAGNOSIS AND TESTING .