Grand Cherokee 2WD V8-4.7L VIN N (2000)
Seat Heater Thermostat: Description and Operation
HEATED SEAT ELEMENT AND SENSOR
The heated seat system includes two seat heating elements in each front seat, one for the seat cushion and the other for the seat back. Two types of
heated seat elements are offered. All Laredo models use two resistor wire heating elements for each seat that are connected in series with the
Heated Seat Module (HSM). All Limited models use two carbon fiber mesh heating elements for each seat that are connected in parallel with the
Memory Heated Seat Module (MHSM). The temperature sensor is a Negative Temperature Coefficient (NTC) thermistor. One temperature sensor
is used for each seat, and it is located on the seat cushion heating element for all models.
The seat heating elements are sewn into the seat cushion cover trim and seat back cover trim units. The heated seat elements and the temperature
sensor cannot be adjusted or repaired and, if faulty or damaged, the seat cushion cover trim unit or seat back cover trim unit must be replaced.
The heated seat elements resist the flow of electrical current. When battery current is passed through the elements, the energy lost by the resistance
of the elements to the current flow is released in the form of heat. The temperature sensor is a NTC thermistor. When the temperature of the seat
cushion cover rises, the resistance of the sensor decreases. The HSM or MHSM supplies a five-volt current to one side of each sensor, and
monitors the voltage drop through the sensor on a return circuit. The MSM or MHSM uses this temperature sensor input to monitor the
temperature of the seat, and regulates the current flow to the seat heating elements accordingly.
