Heated Glass Element Relay: Description and Operation

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 that switches battery current through a fuse in the integrated power module (IPM) to the rear window defogger grid and switches battery current through a positive thermal coefficient (PTC) in the IPM to the outside mirror heating grids. The relay is energized when the relay coil is provided a ground path by the rear window defogger relay control in the front control module (FCM).

The rear window defogger relay is located in the IPM in the engine compartment. See the fuse and relay layout map on the inner surface of the IPM cover for rear window defogger relay identification and location.

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