Heated Glass Element: Description and Operation
HEATED GLASS SYSTEMThe rear window defogger system is used to defog and deice the rear window in cases of freeze up and humid conditions. The rear window defogger switch is located to the right of the mode select knob on the HVAC control module on this model.
The Rear Window Defogger electrical system involves the operation of the Manual Temperature Control (MTC) head, the Body Control Module (BCM), and the rear window defogger relay and wiring. The system consists of a rear glass with two vertical bus bars and a series of electrically connected grid lines fired on the inside surface. The Body Control Module (BCM) operates a relay located in the right side trunk area on all models.
The system consists of a rear glass with two vertical bus bars and a series of electrically connected grid lines on the inside surface. The control switch is located in the HVAC Control Module. The relay is located in the junction block. The timer is located in the Body Control Module (BCM).
Circuit protection for heated grid is provided by:
- A 40 amp EBL fuse located in the power distribution center
- Rear window defogger relay (EBL) located in the Junction Block
When the button is depress to the ON position, current is directed to the rear defogger grid lines. A yellow indicator above the button will illuminate while the defogger is ON. The heated grid lines will heat the rear glass and clear the window surface of fog or frost.
CAUTION: Grid lines can be damaged or scraped off with sharp instruments, care should be taken in cleaning glass or removing foreign materials, decals or stickers. Normal glass cleaning solvents or hot water used with rags or toweling is recommended.
REAR WINDOW DEFOGGER RELAY
The rear window defogger relay is an electromechanical device that switches fused battery current to the rear glass heating grid and the Light-Emitting Diode (LED) indicator of the rear window defogger switch, when the Body Control Module (BCM) rear window defogger timer and logic circuitry grounds the relay coil.
The rear window defogger relay is a International Standards Organization (ISO) relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions.
The rear window defogger relay cannot be repaired or adjusted and, if faulty or damaged, it must be replaced.
The ISO relay consists of an electromagnetic coil, a resistor or diode, and three (two fixed and one movable) electrical contacts. The movable (common feed) relay contact is held against one of the fixed contacts (normally closed) by spring pressure. When the electromagnetic coil is energized, it draws the movable contact away from the normally closed fixed contact, and holds it against the other (normally open) fixed contact.
When the electromagnetic coil is de-energized, spring pressure returns the movable contact to the normally closed position. The resistor or diode is connected in parallel with the electromagnetic coil in the relay, and helps to dissipate voltage spikes that are produced when the coil is de-energized.
REAR WINDOW DEFOGGER SWITCH
The rear window defogger control switch and circuit are integrated into the HVAC control assembly. Refer to the HVAC control assembly for additional information.
When actuating the switch it sends a ground signal to the Body Control Module (BCM). The BCM actuates the relay allowing current to flow through the grid lines for 15 minutes upon initial actuation. Then 10 minutes with each subsequent actuation or until either the switch or ignition is turned OFF. An indicating lamp illuminates the rear window defogger switch.
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.
One temperature sensor is used for each outboard seating position of the front seat, and it is located in the center insert area of the seat cushion cover. 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 sensors are Negative Thermal Coefficient (NTC) thermistors. The sensors for both front seats receive a voltage feed from a single output of the heated seat module, but the module receives individual sensor inputs from the driver side and passenger side sensors.
The heated seat elements and sensors cannot be repaired. If damaged or faulty, the front seat cushion trim cover or front seat back trim cover 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 Switch:
HEATED SEAT SWITCH
The heated seat switch used on vehicles with this option is mounted in the center console. The switch is snapped into a mounting hole in the center console. The heated seat switch incorporates two rotary knobs, one for the driver and one for the front seat passenger. These knobs have numerals 1-6 to indicate the desired rate of supplemental seat heating. The instrument panel wire harness connectors for the heated seat switch is keyed to match the connector receptacle on the switch so that the heated seat switch can only be connected in the proper orientation.
The 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. The two six-position rotating-type switches provide a hard-wired voltage signal to the heated seat module to power the heated seat element of the selected seat and maintain the requested temperature setting.
There are three Light Emitting Diodes (LED's) in the heated seat switch. The first LED illuminates the heated seat symbol on the switch anytime the ignition switch is in the ON position. The remaining LED's illuminate the numbers on the switch, indicating that the system is on.
Fig.4 Heated Seat Control Module:
HEATED SEAT MODULE
Two heated seat modules are used on this vehicle, one for each front seat. The heated seat modules are located under each front seat. The heated seat module has a single connector receptacle that allows the module to be connected to all of the required inputs and outputs through the body wire harness.
The heated seat module is an electronic microprocessor controlled device designed and programmed to use inputs from the ignition switch, the two heated seat switches and the two heated seat sensors to operate and control the heated seat elements in both front seats.
The heated seat module cannot be repaired. If the heated seat module is damaged or faulty, the entire module must be replaced.
The heated seat module operates on fused battery current received from the ignition switch. The module is grounded at all times through the body harness. Inputs to the module include a resistor multiplexed heated seat switch request circuit for each of the two heated seat switches and the heated seat sensor inputs from the seat cushions of each front seat. In response to those inputs the heated seat module controls battery current feeds to the heated seat elements and sensors.
When a heated seat switch (Driver or Passenger) request signal is received by the heated seat module, the module energizes the selected heated seat sensor circuit and the sensor provides the module with an input indicating the surface temperature of the selected seat cushion.
The Low heat set point is about 38 °C (100.4 °F), and the High heat set point is about 42 °C (107.6 °F). If the seat cushion surface temperature input is below the temperature set point for the selected temperature setting, the heated seat module energizes an N-channel Field Effect Transistor (N-FET) within the module which energizes the heated seat elements in the selected seat cushion and back. When the sensor input to the module indicates the correct temperature set point has been achieved, the module de-energizes the N-FET which de-energizes the heated seat elements. The heated seat module will continue to cycle the N-FET as needed to maintain the selected temperature set point.