Liberty Sport 2WD L4-2.4L VIN 1 (2002)
Low Beam Relay: Description and Operation
Fig.11 ISO Micro Relay
HEADLAMP LOW BEAM RELAY
The headlamp low beam relay is located in the Junction Block (JB) below the driver side outboard end of the instrument panel in the passenger
compartment of the vehicle. The headlamp low beam relay is a conventional International Standards Organization (ISO) micro relay (Fig. 37).
Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. The
relay is contained within a small, rectangular, molded plastic housing and is connected to all of the required inputs and outputs by five integral
male spade-type terminals that extend from the bottom of the relay base.
The headlamp low beam relay cannot be adjusted or repaired and, if faulty or damaged, the unit must be replaced.
The headlamp low beam relay is an electromechanical switch that uses a low current input from the Body Control Module (BCM) to control a
high current output to the headlamp low beam filaments. 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 low beam relay terminals are connected to the vehicle electrical system through a connector receptacle in the Junction Block (JB).
The inputs and outputs of the headlamp low beam relay include:
-
Common Feed Terminal - The common feed terminal (30) receives battery current at all times from a fuse in the Power Distribution Center
(PDC) through a fused B(+) circuit.
-
Coil Ground Terminal - The coil ground terminal (85) receives battery current at all times from a fuse in the PDC through a fused B(+)
circuit.
-
Coil Battery Terminal - The coil battery terminal (86) is connected to a control output of the Body Control Module (BCM) through a low
beam relay control circuit. The BCM controls headlamp low beam operation by controlling a ground path through this circuit.
-
Normally Open Terminal - The normally open terminal (87) is connected to the headlamp low beam filaments through the low beam relay
output circuit and provides battery current to the headlamp low beams whenever the relay is energized.
-
Normally Closed Terminal - The normally closed terminal (87A) is not connected in this application.
The headlamp low beam relay can be diagnosed using conventional diagnostic tools and methods.
