Seat Belt Switch - Operation

OPERATION

The driver side seat belt switch is designed to control a path to ground for the seat belt switch sense input of the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN). The passenger side seat belt switch is designed to control a sense input to the Occupant Restraint Controller (ORC). The seat belt switch plunger is actuated by the seat belt webbing wound onto the seat belt retractor spool. When the seat belt tip-half webbing is pulled out of the retractor far enough to engage the seat belt buckle-half, the switch plunger is extended and closes the seat belt switch sense circuit. Conversely, when the seat belt tip-half webbing is wound onto the retractor spool the switch plunger is depressed, opening the sense circuit.

The EMIC monitors the driver side seat belt switch status through the hard wired input, then controls the illumination of the seatbelt indicator and the generation of audible electronic chime tones based upon that input. The ORC monitors the passenger side seat belt switch and Occupant Detection Sensor (ODS) input status through hard wired inputs. If the ORC logic determines that the seat belt is not buckled while the seat is occupied, it sends an electronic message to the EMIC over the Controller Area Network (CAN) data bus requesting seat belt indicator illumination.

The driver side seat belt switch receives ground through its connection to the body wire harness from another take out of the body wire harness. An eyelet terminal connector on that ground take out is secured under a ground screw. The driver side seat belt switch is connected in series between ground and the driver side seat belt switch sense input of the EMIC. The passenger side seat belt switch receives a clean ground from the ORC and is connected in series between the clean ground and the passenger side seat belt switch input of the ORC.

The hard wired circuits between the seat belt switches and the EMIC (driver side) or ORC (passenger side) 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 switches or the electronic controls or communication between other modules and devices that provide features of the Supplemental Restraint System (SRS). The most reliable, efficient, and accurate means to diagnose the seat belt switches or the electronic controls and communication related to seat belt switch operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.