Seat Sensor/Switch: Description and Operation
The 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 seat belt switch input.
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, and the EMIC senses the status of the front seat belt through its connection to the seat wire
harness. The EMIC also monitors the condition of the seat belt switch circuits 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 circuits.
The hard wired circuits between the seat belt switch and the EMIC 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.