Grand Cherokee 2WD V6-3.7L (2008)
Fog/Driving Lamp Relay: Description and Operation
Operation
OPERATION
The front fog lamp relay is an electromechanical switch that uses a low current input from the Front Control Module (FCM) (located in the Integrated
Power Module/IPM) to control a high current output to the front fog lamps. Within the relay are an electromagnetic coil, a movable contact and two
fixed contact points. A resistor is connected in parallel with the coil, and helps to dissipate voltage spikes and electromagnetic interference that can be
generated as the field of the relay coil collapses.
The movable common supply 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 field draws the movable contact away from the normally closed contact, and holds it
against the normally open contact. When the relay coil is de-energized, spring pressure returns the movable contact back against the normally closed
contact.
The inputs and outputs of the front fog lamp relay include:
-
Common Supply Terminal (30) - The common feed terminal is connected to a fused B(+) circuit at all times.
-
Coil Ground Terminal (85) - The coil ground terminal is connected to a control output of the FCM through a front fog lamp relay control circuit.
The FCM controls front fog lamp operation by controlling a ground path through this circuit.
-
Coil Battery Terminal (86) - The coil battery terminal is connected to a fused B(+) circuit at all times.
-
Normally Open Terminal (87) - The normally open terminal is connected to the front fog lamps through a front fog lamp relay output circuit and
provides battery voltage to the front fog lamps whenever the relay is energized.
-
Normally Closed Terminal (87A) - The normally closed terminal is not connected to any circuit in this application, but will have battery voltage
present whenever the relay is de-energized.
The front fog lamp 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.
