Grand Cherokee 2WD Limited V8-4.7L (2002)
Seat Belt Buckle Switch: Description and Operation
Fig.22 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 are integral to each front seat belt buckle. The front seat belt buckles are each 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 each front seat
cushion. The seat belt switches are connected to the vehicle electrical system through a two-lead pigtail wire and connector on the 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 seat belt buckle-half unit must be replaced.
The seat belt switches are designed to provide a status signal to the seat belt switch sense inputs of the Airbag Control Module (ACM) indicating
whether the front seat belts are fastened. The ACM uses the seat belt switch inputs 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 to the field of the
permanent magnet, which 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 front seat belts. 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 front seat belts through its pigtail wire
connection to the airbag overlay wire harness. The ACM 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 either seat belt switch circuit. For proper
diagnosis of the seat belt switches, a DRB III scan tool is required. Refer to the appropriate diagnostic information.
