Rear Window Defogger Relay
Rear Window Defogger Relay
Description
The rear window defogger relay, also known as Electric Backlight (EBL) relay (1) is an International Standards Organization (ISO) type relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal functions and patterns (2). The EBL relay is a electromechanical device that switches fused battery current to the rear window defogger grid and to the outside rear view mirror heating grids, when equipped. The relay is energized when the relay coil is provided a ground path by the control circuitry within the Totally Integrated Power Module (TIPM).
The relay is located in the TIPM inside the engine compartment.
Operation
The rear window defogger relay is an electromechanical switch that uses a low current input controlled by the TIPM to control the high current output to the rear window defogger grid lines and to the heated outside mirrors, when equipped. The movable, common feed relay contact is held against the fixed, normally closed relay contact by spring pressure. When the electromagnetic relay coil is energized, it draws the movable common feed relay contact away from the fixed, normally closed relay contact and, holds it against the fixed, normally open relay contact. This action allows high current to flow to the rear window defogger grid lines.
When the relay coil is de-energized, spring pressure returns the movable relay contact back against the fixed, normally closed contact point. The resistor or diode is connected in parallel with the relay coil, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.
The relay terminals are connected to the vehicle electrical system through a receptacle in the TIPM located in the engine compartment. The inputs and outputs of the relay include:
• Terminal (30) receives battery current at all times.
• Terminal (85) receives a ground through the EBL control circuit of the TIPM only when the module electronically pulls the circuit to ground.
• Terminal (86) receives battery current at all times.
• Terminal (87) provides battery current to the rear window defogger grid and to the heated outside mirrors, only when the relay coil is energized.
• Terminal (87A) is not connected to any circuit in this application, but provides a battery current output only when the relay coil is de-energized.
The relay cannot be repaired and must be replaced if inoperative or damaged. See wiring information for diagnosis and testing of the ISO relay and for complete rear window defogger wiring diagrams.