Heated Glass Element: Description and Operation

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.

The rear window defogger system consists of a rear glass with two vertical electrical bus bars linked by a series of grid lines fired onto the inside surface of the optional heated rear window.

Rear Window Defogger Switch:

The rear window defogger system is turned On or Off by a switch integral to the A/C-heater control located at the center of the instrument panel and by the timer and logic circuitry located within the body control module (BCM).

Circuit protection is provided by a 10 amp fuse located in the junction block.

Rear Window Defogger Relay:

The rear window defogger relay is a International Standards Organization (ISO)-type relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. The rear window defogger relay is a electromechanical device. When the instrument cluster rear window defogger timer and logic circuitry grounds the relay coil, the rear window defogger relay switches battery current through a fuse and to the rear glass heating grid and also to the light-emitting diode (LED) indicator of the rear window defogger switch and to the heating elements of the outside mirrors (when equipped with heated mirrors).

The rear window defogger relay is located in the junction block, on the left side of the instrument panel inboard to the center of the vehicle (just to the left and above the brake pedal or behind the knee blocker). See the fuse and relay layout map on the cover of the junction block for rear window defogger relay identification and location.

The rear window defogger relay cannot be repaired or adjusted and, if faulty or damaged, it must be replaced.

Rear Window Defogger Switch:

The rear window defogger switch is integrated into the A/C-heater control mounted in the center of the instrument panel. The rear window defogger switch and the rear window defogger LED indicator cannot be repaired and, if faulty or damaged, the A/C-heater control must be replaced.

When the rear window defogger switch is pressed to the On position, current is directed to the rear defogger grid lines and the heated power mirrors (if equipped). The heated grid lines heat the glass to help clear the rear window and side mirror surfaces of fog or frost.

The rear window defogger system is controlled by a momentary switch located in the A/C-heater control on the instrument panel. An amber indicator lamp in the switch will illuminate to indicate when the rear window defogger system is turned On. The body control module (BCM) circuitry controls the rear window defogger system through a hard-wired control output to the rear window defogger relay. The rear window defogger timer and logic circuitry cannot be adjusted or repaired and, if faulty or damaged, the BCM must be replaced.

NOTE: The rear window defogger turns off automatically after approximately 10 minutes of operation.

The defogger system will be automatically turned off after a programmed time interval of about ten minutes. After the initial time interval has expired, if the defogger switch is turned on again during the same ignition cycle, the defogger system will automatically turn off after about five minutes.

The defogger system will automatically shut off if the ignition switch is turned to the Off position, or it can be turned off manually by pressing the defogger switch a second time.

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 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.

Refer to the appropriate wiring information for diagnosis and testing of the ISO relay and for complete rear window defogger system wiring diagrams.

An LED indicator will illuminate when the rear window defogger switch is activated. The switch energizes the timing circuit integral to the body control module (BCM) which then activates the rear window defogger relay. The rear window defogger relay controls the current to flow to the grids of the rear window defogger. The rear window defogger system will operate for approximately ten minutes or until the rear window defogger switch or ignition switch is turned off.

The rear window defogger switch cannot be repaired and, if faulty or damaged, it must be replaced.