Seat Belt Switch: Operation

The driver side front seat belt switch is a hard wired input to the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN), which also controls the seat belt indicator based upon the status of the driver side seat belt switch input. On vehicles with the Occupant Classification System (OCS) the passenger side seat belt switch is designed to provide a status signal to the seat belt switch sense input of the Occupant Restraint Controller (ORC) indicating whether the passenger side front seat belt is fastened. The ORC uses the seat belt switch signal as an additional logic input to determine the status of the passenger side front seat belt. The ORC then sends electronic messages to the EMIC over the Controller Area Network (CAN) data bus to control the seat belt indicator based upon the status of the passenger side seat belt switch input and, on early production vehicles only, based upon electronic messages from the Occupant Classification Module (OCM) indicating whether or not the passenger side front seat is occupied.

A spring-loaded slide with a small window-like opening is integral to the buckle latch mechanism. When a seat belt tip-half is inserted and latched into the seat belt buckle, the slide is pushed downward and the window of the slide exposes the Hall Effect Integrated Circuit (IC) chip within the buckle. The field of the permanent magnet induces a current within the chip. The chip provides this induced current as an output to the ORC. When the seat belt is unbuckled, the spring-loaded slide moves upward and shields the IC from the field of the permanent magnet, causing the output current from the seat belt switch to be reduced.

The seat belt switch receives a supply current from the EMIC (driver side) or the ORC (passenger side), and the EMIC or ORC senses the status of the front seat belt through its connection to the seat wire harness. The EMIC and ORC also monitor the condition of the seat belt switch circuit and will illuminate the airbag indicator in the EMIC then store a Diagnostic Trouble Code (DTC) for any fault that is detected in the seat belt switch circuit.

The hard wired circuits between the seat belt switches and the ORC or the EMIC may be diagnosed using conventional diagnostic tools and procedures. Refer to the SYSTEM WIRING DIAGRAMS article. 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. 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 ELECTRICAL DIAGNOSTIC article.