Seat Temperature Element: Description and Operation
HEATED SEAT SYSTEMIndividually controlled electrically heated front seats are available factory-installed optional equipment on the Durango models that are also equipped with the optional leather trim package. Vehicles with this option can be visually identified by the two separate heated seat switches mounted in the center console. The heated seat system allows the front seat driver and passenger to select from two different levels of supplemental electrical seat heating, or no seat heating to suit their individual comfort requirements. The heated seat system for this vehicle includes the following major components:
- The heated seat switches, including two heated seat Light-Emitting Diode (LED) indicator lamps and three back lighting LED's for each switch.
- The heated seat module, also referred to as the Seat Heat Interface Module (SHIM), which contains the solid state electronic control and diagnostic logic circuitry for the heated seat system.
- The heated seat elements and sensors, which are integral to the individual front seat cushion and front seat back trim covers.
Following are general descriptions of the major components in the heated seat system. See the owner's manual in the vehicle glove box for more information on the features, use and operation of the heated seat system. Refer to Power Seat for the location of complete heated seat system wiring diagrams.
The heated seat module receives fused battery current through Junction Block (JB) only when the ignition switch is in the run position. The heated seat switches receive battery current through a fused ignition switch output (run) circuit only when the ignition switch is in the Run position. The heated seat module shares a common ground circuit with each of the heated seat elements. The heated seat elements will only operate when the surface temperature of the seat cushion cover at the heated seat sensors is below the designed temperature set points of the system.
The heated seat module will automatically turn OFF the heated seat elements if it detects a short in the heated seat element circuit or a heated seat sensor value that is out of range. The heated seat system will also be turned OFF automatically whenever the ignition switch is turned to any position except Run. If the ignition switch is turned to the OFF position the heated seat will remain OFF after the ignition switch is turned to the ON position until a heated seat switch is depressed again.
The heated seat module monitors inputs from the heated seat sensors and the heated seat switches. In response to these inputs the heated seat module uses its internal programming to control outputs to the heated seat elements in both front seats and to control the heated seat LED indicator lamps located in both of the heated seat switches. The heated seat module is also programmed to provide a self-diagnostic capability. When the module detects certain failures within the heated seat system, it will provide a visual indication of the failure by flashing the indicator lamps in the heated seat switches.
DRIVER HEATED SEAT SWITCH
The heated seat switches used on vehicles with this option are both mounted in the center console. The two switches are snapped into mounting holes in the center console. The two heated seat switches are identical in appearance and construction, except for the location of a keyway in the single connector receptacle and the housing on the back of each switch. The instrument panel wire harness connectors for the heated seat switches are keyed to match the connector receptacles on the switches so that the two heated seat switches can only be connected to the proper heated seat.
The momentary bidirectional rocker-type heated seat switch provides a resistor-multiplexed signal to the heated seat module. Each switch has a center neutral position and momentary Low and High positions so that both the driver and the front seat passenger can select a preferred seat heating mode. Each heated seat switch has two Light-Emitting Diode (LED) indicator lamps, which indicate the selected mode (Low or High) of the seat heater for each seat and to provide diagnostic feedback for the heated seat system. Each switch also has three other LED indicator lamps, which provides back lighting of the switch nomenclature when the ignition switch is in the Run position.
The five LED indicator lamps in each heated seat switch cannot be repaired. If the indicator or back lighting lamps are faulty or damaged, the individual heated seat switch unit must be replaced.
The heated seat switches receive battery current through a fused ignition switch output (run) circuit when the ignition switch is in the ON position. Depressing the heated seat switch rocker to its momentary High or Low position provides a hard-wired resistor multiplexed voltage request signal to the heated seat module to power the heated seat element of the selected seat and maintain the requested temperature setting. If the heated seat switch is depressed to a different position (Low or High) than the currently selected state, the heated seat module will change states to support the new selection. If a heated seat switch is depressed a second time to the same position as the currently selected state, the heated seat module interprets the second input as a request to turn the seat heater off. The heated seat module will then turn the heated seat elements for that seat OFF.
The indicator lamps in the heated seat switches receive battery current through a fused ignition switch output (run) circuit when the ignition switch is in the ON position. The ground side of each indicator lamp is controlled by a separate (high or low/ driver or passenger) indicator lamp driver circuit by the heated seat module. The heated seat module control of the switch indicator lamps also allows the module to provide diagnostic feedback to the vehicle operator to indicate monitored heated seat system faults by flashing the indicator lamps ON and OFF. One side of the back lighting LED's in each heated seat switch are connected in series to ground at all times. The other side of the LED's are connected to the ignition switch run circuit. These LED's are energized when the ignition switch is turned to the Run position.
PASSENGER HEATED SEAT SWITCH
The heated seat switches used on vehicles with this option are both mounted in the center console. The two switches are snapped into mounting holes in the center console. The two heated seat switches are identical in appearance and construction, except for the location of a keyway in the single connector receptacle and the housing on the back of each switch. The instrument panel wire harness connectors for the heated seat switches are keyed to match the connector receptacles on the switches so that the two heated seat switches can only be connected to the proper heated seat.
The momentary bidirectional rocker-type heated seat switch provides a resistor-multiplexed signal to the heated seat module. Each switch has a center neutral position and momentary Low and High positions so that both the driver and the front seat passenger can select a preferred seat heating mode. Each heated seat switch has two Light-Emitting Diode (LED) indicator lamps, which indicate the selected mode (Low or High) of the seat heater for each seat and to provide diagnostic feedback for the heated seat system. Each switch also has three other LED indicator lamps, which provides back lighting of the switch nomenclature when the ignition switch is in the Run position.
The five LED indicator lamps in each heated seat switch cannot be repaired. If the indicator or back lighting lamps are faulty or damaged, the individual heated seat switch unit must be replaced.
The heated seat switches receive battery current through a fused ignition switch output (run) circuit when the ignition switch is in the ON position. Depressing the heated seat switch rocker to its momentary High or Low position provides a hard- wired resistor multiplexed voltage request signal to the heated seat module to power the heated seat element of the selected seat and maintain the requested temperature setting. If the heated seat switch is depressed to a different position (Low or High) than the currently selected state, the heated seat module will change states to support the new selection. If a heated seat switch is depressed a second time to the same position as the currently selected state, the heated seat module interprets the second input as a request to turn the seat heater OFF. The heated seat module will then turn the heated seat elements for that seat OFF.
The indicator lamps in the heated seat switches receive battery current through a fused ignition switch output (run) circuit when the ignition switch is in the ON position. The ground side of each indicator lamp is controlled by a separate (high or low/driver or passenger) indicator lamp driver circuit by the heated seat module. The heated seat module control of the switch indicator lamps also allows the module to provide diagnostic feedback to the vehicle operator to indicate monitored heated seat system faults by flashing the indicator lamps ON and OFF. One side of the back lighting LED's in each heated seat switch are connected in series to ground at all times. The other side of the LED's are connected to the ignition switch run circuit. These LED's are energized when the ignition switch is turned to the Run position.
HEATED SEAT ELEMENT
Vehicles equipped with the optional heated seat system have two sets of electrically operated heating element grids located in each outboard seating position of the front seat, one set for the seat cushion and the other set for the seat back. Each of the heated seat element grids consists of a single length of resistor wire that is routed in a zigzag pattern and captured between the leather trim cover and the foam rubber backing on the underside of its respective seat cushion trim cover and seat back trim cover assembly. Short pigtail wires with connectors are soldered to each end of each resistor wire element grid, which connect all of the element grids for each seating position to each other in series with the heated seat module through the seat wire harness.
The heated seat sensors and their pigtail wires are also captured between the leather trim cover and the foam rubber backing on the underside of their respective seat cushion trim cover assemblies.
The heated seat elements and sensors cannot be repaired. If damaged or faulty, the heating element assembly must be replaced.
One end of the heated seat element resistor wire is connected to a ground feed at all times through a splice in the heated seat module ground circuit. Battery current is directed to the other end of the heated seat element resistor wire by the energized N-channel Field Effect Transistor (N-FET) located within the heated seat module. The heated seat module will energize the N-FET only when the heated seat switch is in the Low or High position and the heated seat sensor indicates that the seat cushion surface temperature is below the selected (Low or High) temperature set point. As electrical current passes through the heating element grid, the resistance of the wire used in the element disperses some of that electrical current in the form of heat. The heat produced by the heated seat element grid then radiates through the underside of the seat cushion and seat back trim covers, warming the seat cover and its occupant.
The resistance of the heated seat sensor increases and decreases as the surface temperature of the seat cushion cover changes. The heated seat module supplies each sensor with a voltage feed, then detects the sensor resistance by monitoring the voltage of the separate sensor return circuits. The heated seat module compares the heated seat sensor resistance (seat cushion surface temperature) with the heated seat switch resistance (Low or High set point) to determine when the heated seat element grids need to be cycled ON or OFF in order to maintain the selected temperature set point.
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.