Grand Cherokee 2WD V8-4.7L VIN J (2004)
Seat Belt Buckle Switch: Description and Operation
Fig. 43 Front Seat Belt Buckle
SEAT BELT SWITCH
The seat belt switch for this model is actually a Hall Effect-type sensor. This sensor consists of a fixed-position, Hall Effect Integrated Circuit (IC)
chip and a small permanent magnet that is integral to the driver side front seat belt buckle. The driver side front seat belt buckle is located on a
stamped steel stanchion within a molded plastic scabbard and secured with a screw to the floor panel transmission tunnel on the inboard side of the
driver side front seat cushion. The seat belt switch is connected to the vehicle electrical system through a two-lead pigtail wire and connector on the
driver side front seat belt buckle-half, which is connected to a wire harness connector and take out of the body wire harness on vehicles with manual
seat adjusters, or to a connector and take out of the power seat wire harness on vehicles with power seat adjusters. A radio noise suppression capacitor
is connected in parallel with the IC where the two pigtail wire leads connect to the IC pins.
The seat belt switch cannot be adjusted or repaired and, if faulty or damaged, the entire driver side front seat belt buckle-half unit must be replaced.
The seat belt switch is designed to provide a status signal to the seat belt switch sense input of the Air- bag Control Module (ACM) indicating whether
the driver side front seat belt is fastened. The ACM uses the seat belt switch input as a factor in determining what level of force with which it should
deploy the multistage driver and passenger airbags. In addition, the ACM sends electronic messages to the ElectroMechanical Instrument Cluster
(EMIC) to control the seat belt indicator based upon the status of the driver side front seat belt switch.
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 ACM, which monitors
the current to determine the status of the driver side front seat belt. 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 ACM, and the ACM senses the status of the driver side front seat belt through its pigtail wire
connection to the airbag overlay wire harness. The ACM also monitors 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. For proper diagnosis of
the seat belt switch, a DRBIII scan tool is required. Refer to the appropriate diagnostic information.
