Rear Defogger Relay - Operation

OPERATION

The rear window defogger (EBL) relay is an electromechanical switch that uses a low current input controlled by the front control module (FCM) to control the high current output to the rear window defogger grid lines. 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 EBL relay terminals are connected to the vehicle electrical system through a receptacle in the integrated power module (IPM). The inputs and outputs of the EBL relay include:

- The common feed terminal (E) receives fused battery current through a B(+) circuit at all times.
- The coil ground terminal (D) receives a ground input from the FCM through the EBL control circuit only when the FCM electronically pulls the control circuit to ground.
- The coil battery terminal (B) receives fused battery current through the ignition switch circuit only when the switch is in RUN.
- The normally open terminal (A) provides battery current to the rear window defogger grid lines through the EBL relay output circuit only when the EBL relay coil is energized.
- The normally closed terminal (C) is not connected to any circuit in this application, but provides a battery current output only when the EBL relay coil is de-energized.

The EBL micro-relay cannot be repaired and must be replaced if inoperative or damaged. See Wiring Information for diagnosis and testing of the ISO-standard micro-relay and for complete rear window defogger (EBL) wiring diagrams.