Headlamp Washer Relay - Operation

OPERATION

The headlamp washer relay is an electromechanical switch that uses a low current input from the Body Control Module (BCM) (also known as the Common Body Controller/CBC) to control a high current output to the headlamp washer pump/motor unit. The movable common feed contact point is held against the fixed normally closed contact point by spring pressure. When the relay coil is energized, an electromagnetic field is produced by the coil windings. This electromagnetic field draws the movable relay contact point away from the fixed normally closed contact point, and holds it against the fixed normally open contact point. When the relay coil is de-energized, spring pressure returns the movable contact point back against the fixed normally closed contact point. A resistor is connected in parallel with the relay coil in the relay, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.

The headlamp washer relay terminals are connected to the vehicle electrical system through a dedicated take out and connector of the Front End Module (FEM) wire harness. The inputs and outputs of the headlamp washer relay include:

- Common Feed Terminal - The common feed terminal (30) is connected to battery current on a fused B(+) circuit from a fuse in the engine compartment Power Distribution Center (PDC) at all times.
- Coil Ground Terminal - The coil ground terminal (85) is connected to battery current on a fused run relay output circuit from a fuse in the engine compartment PDC at all times. This circuit is energized by the run relay only while the engine is running.
- Coil Battery Terminal - The coil battery terminal (86) is connected to a low side driver output from the BCM on a headlamp washer relay control circuit. The BCM controls headlamp washer system operation through this relay connection.
- Normally Open Terminal - The normally open terminal (87) is connected through a headlamp washer relay output circuit to the headlamp washer pump/motor unit at all times. When the relay is energized, the normally open terminal of the relay is connected to battery current from the fuse in the engine compartment PDC.
- Normally Closed Terminal - The normally closed terminal (87A) is not connected to any circuit in this application, but will have battery current present whenever the headlamp washer relay coil is not energized.

The headlamp washer relay as well as the hard wired inputs and outputs of the relay may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information. However, conventional diagnostic methods will not prove conclusive in the diagnosis of the electronic controls or the communication between modules and other devices that provide some features of the headlamp washer system. The most reliable, efficient, and accurate means to diagnose the headlamp washer relay or the electronic controls and communication related to headlamp washer system operation requires the use of a diagnostic scan tool. Refer to the appropriate diagnostic information.