Grand Cherokee 2WD Limited V8-4.7L (2002)
Wiper Relay: Description and Operation
Relay-Wiper High/Low
Fig.25 ISO Micro Relay
WIPER HIGH/LOW RELAY
The wiper high/low relay is located in the Power Distribution Center (PDC) in the engine compartment near the battery The wiper high/low relay is a
conventional International Standards Organization (ISO) micro relay. 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 wiper high/low relay cannot be adjusted or repaired and, if faulty or damaged, the unit must be replaced.
The wiper high/low 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 front wiper motor. 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 wiper high/low relay terminals are connected to the vehicle electrical system through a connector receptacle in the Power Distribution Center
(PDC). The inputs and outputs of the wiper high/low relay include:
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Common Feed Terminal - The common feed terminal (30) is connected to the output of the wiper ON/OFF relay at all times through the wiper
ON/OFF relay output circuit.
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Coil Ground Terminal - The coil ground terminal (85) is connected to a control output of the Body Control Module (BCM) through a front wiper
high/ low relay control circuit. The BCM controls front wiper motor operation by controlling a ground path through this circuit.
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Coil Battery Terminal - The coil battery terminal (86) receives battery current at all times from a circuit breaker in the Junction Block (JB)
through a fused ignition switch output (run-acc) circuit.
-
Normally Open Terminal - The normally open terminal (87) is connected to the high speed brush of the front wiper motor through a front wiper
high/low relay high speed output circuit, and is connected to the high speed brush whenever the relay is energized.
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Normally Closed Terminal - The normally closed terminal (87A) is connected to the low speed brush of the front wiper motor through a front
wiper high/low relay low speed output circuit, and is connected to the low speed brush whenever the relay is de-energized.
The wiper high/low relay can be diagnosed using conventional diagnostic tools and methods.
