RAM 1500 Truck 4WD V8-5.9L VIN Z (2002)
Wiper Relay: Description and Operation
Relay-Wiper High/Low
Fig. 18 ISO Micro Relay
WIPER HIGH/LOW RELAY
The wiper switch is a direct input to the instrument cluster. The instrument cluster sends a PCI bus request to the FCM to actuate the wiper
high/low relay.
The relay switches power between the low speed and high speed brush of the wiper motor. The wiper high/low relay is then actuated through the
low side control circuit. This circuit is electronically controlled and continuously monitored for malfunctions.
The wiper high/low relay is located in the Integrated Power Module (IPM) 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 Front Control Module (FCM) to control a high
current output to the 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 Integrated Power Module
(IPM). 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 Front Control Module (FCM) through a wiper
high/low relay control circuit. The FCM controls 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 when the ignition switch is in the ON or Accessory positions
from a fuse in the Integrated Power Module (IPM) through a fused ignition switch output (run-acc) circuit.
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Normally Open Terminal - The normally open terminal (87) is connected to the high speed brush of the wiper motor through a wiper
high/low relay high speed output circuit, and is connected to the high speed brush whenever the relay is energized.
-
Normally Closed Terminal - The normally closed terminal (87A) is connected to the low speed brush of the wiper motor through a 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. However, conventional diagnostic methods may not
prove conclusive in the diagnosis of the instrument cluster, the Front Control Module (FCM), or the electronic message inputs to or outputs from
the instrument cluster and the FCM that control the operation of the wiper high/low relay. The most reliable, efficient, and accurate means to
diagnose the wiper high/low relay, the instrument cluster, the FCM, or the electronic message inputs and outputs related to the wiper high/low
