Seat Temperature Element: Description and Operation
Fig.1 Heated Seat Switch Locations:
HEATED SEAT SYSTEM
Vehicles with the heated seat option can be visually identified by the two separate heated seat switches located in the instrument panel center stack, just above the radio. The heated seat system allows the front seat driver and passenger to select from two different levels of supplemental electrical seat heating (HI/LO), or no seat heating to suit their individual comfort requirements. The heated seat system for this vehicle includes the following major components, which are described in further detail later in this section:
- Heated Seat Elements - Four heated seat elements are used per vehicle, two for each front seat. One heated seat element is integral to each front seat trim cover, one in the seat back and one in the seat bottom (cushion). Service replacement heating elements are available, refer to heated seat elements later in this section for additional information.
- Heated Seat Modules - Two heated seat modules are used per vehicle. One module is mounted to each of the seat cushion pans, located under the forward edge of each front seat. Refer to heated seat module in the electronic control modules section of the service manual for additional information.
- Heated Seat Sensors - Two heated seat sensors are used per vehicle, one for each front seat. The heated seat sensors are integral to each of the heated seat bottoms (cushions).
- Heated Seat Switch - Two heated seat switches are used per vehicle, one for the driver and one for the passenger side front seats. The switches are mounted to in the instrument panel center stack. Refer to the description of the heated seat switch later in this section for additional information.
Hard wired circuitry connects the heated seat system components to each other through the electrical system of the vehicle. These hard wired circuits are integral to several wire harnesses, which are routed throughout the vehicle and retained by many different methods. These circuits may be connected to each other, to the vehicle electrical system and to the heated seat system components through the use of a combination of soldered splices and splice block connectors. Refer to Wiring for complete system wiring schematics. The wiring information also includes the proper wire and connector repair procedures, further details on wire harness routing and retention, as well as pin-out and location views for the various wire harness connectors, splices and grounds.
The heated seat system components operate on battery current received through a fuse in the Integrated Power Module (IPM) on a fused ignition switch output (run-acc) circuit so that the system will only operate when the ignition switch is in the ON or Accessory positions. The heated seat system will be turned OFF automatically whenever the ignition switch is turned to any position except ON or Accessory Also, the heated seat system will not operate when the surface temperature of the seat cushion cover at either heated seat sensor is above the designed temperature set points of the system. The heated seat system has a self-diagnostic capability. When certain failures are detected within the heated seat system, the system will provide a visual indication of the failure by flashing the Light Emitting Diode (LED) indicator lamps located in the heated seat switches. See the owner's manual in the vehicle glove box for more information on the features, use and operation of the heated seat system.
Fig.1 Heated Seat Switch Locations:
DRIVER HEATED SEAT SWITCH
The heated seat switches are mounted in the instrument panel center bezel. The two three position rocker-type switches, one switch for each front seat, are incorporated into one large switch assembly that also includes the hazard, rear window wiper and washer switches. The heated seat switches provide a resistor multiplexed signal to the Heated Seat Module (HSM) through separate hard wired circuits. Each switch has an OFF, Low, and High position so that both the driver and the front seat passenger can select a preferred seat heating mode. Each switch has two Light-Emitting Diodes (LED) which light to indicate that the heater for the seat is turned on.
The heated seat switches and their LEDs cannot be repaired. If either switch or LED is faulty or damaged, the entire switch assembly must be replaced.
There are three positions that can be selected with each of the heated seat switches: OFF, Low, or High. When the left side of the switch rocker is fully depressed, the Low position is selected and the low position LED indicator illuminates. When the right side of the switch rocker is fully depressed, the High position is selected and the high position LED indicator illuminates. When the switch rocker is moved to its neutral position (middle), OFF is selected and both LED indicators are extinguished.
Both switches provide separate resistor multiplexed hard wire inputs to the Heated Seat Module (HSM) to indicate the selected switch position. The heated seat module responds to the heated seat switch status messages by controlling the output to the seat heater elements of the selected seat. The Low heat position set point is about 36 °C (97 °F), and the High heat position set point is about 41 °C (105 °F).
HEATED SEAT ELEMENT
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. The two elements for each seat that are connected in series with the Heated Seat Module (HSM). 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 element assembly must be replaced. Refer to the procedure in this section.
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 heated seat module supplies a five-volt current to one side of each sensor, and monitors the voltage drop through the sensor on a return circuit. The heated seat module uses this temperature sensor input to monitor the temperature of the seat, and regulates the current flow to the seat heating elements accordingly.
HEATED SEAT SENSOR
Two heated seat sensors are used per vehicle, one in each front seat cushion heating element. The heated seat temperature sensor is a Negative Temperature Coefficient (NTC) thermistor.
The heated seat sensors cannot be repaired or adjusted and if found to be faulty, the complete heated seat cushion element must be replaced.
The temperature sensor is a NTC thermistor. When the temperature of the seat cushion cover rises, the resistance of the sensor decreases. The heated seat module supplies a five-volt current to one side of each sensor, and monitors the voltage drop through the sensor on a return circuit. The heated seat module uses this temperature sensor input to monitor the temperature of the seat, and regulates the current flow to the seat heating elements accordingly.
Fig.1 Heated Seat Switch Locations:
PASSENGER HEATED SEAT SWITCH
The heated seat switches are mounted in the instrument panel center bezel. The two three position rocker-type switches, one switch for each front seat, are incorporated into one large switch assembly that also includes the hazard, rear window wiper and washer switches. The heated seat switches provide a resistor multiplexed signal to the Heated Seat Module (HSM) through separate hard wired circuits. Each switch has an OFF, Low, and High position so that both the driver and the front seat passenger can select a preferred seat heating mode. Each switch has two Light-Emitting Diodes (LED) which light to indicate that the heater for the seat is turned on.
The heated seat switches and their LEDs cannot be repaired. If either switch or LED is faulty or damaged, the entire switch assembly must be replaced.
There are three positions that can be selected with each of the heated seat switches: OFF, Low, or High. When the left side of the switch rocker is fully depressed, the Low position is selected and the low position LED indicator illuminates. When the right side of the switch rocker is fully depressed, the High position is selected and the high position LED indicator illuminates. When the switch rocker is moved to its neutral position (middle), OFF is selected and both LED indicators are extinguished.
Both switches provide separate resistor multiplexed hard wire inputs to the Heated Seat Module (HSM) to indicate the selected switch position. The heated seat module responds to the heated seat switch status messages by controlling the output to the seat heater elements of the selected seat. The Low heat position set point is about 36 °C (97 °F), and the High heat position set point is about 41 °C (105 °F).