Rear Window Defogger Relay - Chrysler 300M Service Manual

LH
REAR WINDOW DEFOGGER
RELAY
DESCRIPTION
The rear window defogger relay is an electrome-
chanical device that switches fused battery current to
the rear glass heating grid and the Light-Emitting
Diode (LED) indicator of the rear window defogger
switch, when the Body Control Module (BCM) rear
window defogger timer and logic circuitry grounds
the relay coil. The rear window defogger relay is
located in the right rear trunk area behind the car-
peting.
The rear window defogger relay is a International
Standards Organization (ISO) relay. Relays conform-
ing to the ISO specifications have common physical
dimensions, current capacities, terminal patterns,
and terminal functions.
The rear window defogger relay cannot be repaired
or adjusted and, if faulty or damaged, it must be
replaced.
OPERATION
The ISO relay consists of an electromagnetic coil, a
resistor or diode, and three (two fixed and one mov-
able) electrical contacts. The movable (common feed)
POTENTIAL PROBLEM
NO PROBLEM. VOLTAGES AS
EXPECTED WITH THE SYSTEM
OFF.
NO PROBLEM. VOLTAGES AS
EXPECTED WITH THE SYSTEM
ON.
RELAY CONTACTS NOT CLOSING.
REPLACE RELAY.
WIRING OPEN BETWEEN BODY
CONTROL MODULE AND REAR
WINDOW DEFOGGER RELAY, OR,
DEFECTIVE BODY CONTROL
MODULE.
REAR WINDOW DEFOGGER RELAY TEST
SYSTEM
ON OR OFF
WITH
ENGINE
RUNNING
OFF
ON
ON
ON
relay contact is held against one of the fixed contacts
(normally closed) by spring pressure. When the elec-
tromagnetic coil is energized, it draws the movable
contact away from the normally closed fixed contact,
and holds it against the other (normally open) fixed
contact.
When the electromagnetic coil is de-energized,
spring pressure returns the movable contact to the
normally closed position. The resistor or diode is con-
nected in parallel with the electromagnetic coil in the
relay, and helps to dissipate voltage spikes that are
produced when the coil is de-energized.
DIAGNOSIS AND TESTING - REAR WINDOW
DEFOGGER RELAY
(1) Stop the engine. Connect the negative lead of a
0-15 volt range voltmeter to a known good vehicle
electrical ground.
(2) Reconnect rear window grid connections if dis-
connected for the Fuse and Electrical Short Test.
Start the engine check the voltages present at the
rear window defogger relay and rear window defog-
ger grid (Fig. 3). Refer to the Rear Window Defogger
Relay Test table for diagnosis.
VOLTAGE AT REAR WINDOW
DEFOGGER RELAY POINT TO
GOOD VEHICLE GROUND
1 2 3
MORE MORE
THAN THAN 0
11 11
MORE MORE MORE
THAN THAN THAN
11 11 11
MORE MORE
THAN THAN 0
11 11
MORE MORE
THAN THAN 0
11 11
HEATED GLASS 8G - 5
VOLTAGE AT
REAR WINDOW
DEFOGGER
GRID TO GOOD
VEHICLE
GROUND
4 A B
MORE
THAN 0
11
LESS MORE LESS
THAN THAN THAN
1.0 11 1.0
LESS
THAN 0
1.0
MORE
THAN 0
11
0
0
0