Pontiac Fiero 1988 Service Manual page 1046

REAR D E F O G G E R : C49
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D: REAR DEFOGGER TEST
With the Ignition Switch in RUN, and the
Defogger Control Switch pressed ON, connect
one lead of a test lamp to ground. From inside
the car at the Rear Window Defogger, lightly
touch the other lead to each grid line, and slowly
move it along the length of the grid. The bril-
liance of the test lamp bulb should increase as
the test lamp is moved from left (passenger's
side) to right (driver's side).
• If the test lamp does not light along any one
of the grid lines, check PPL/WHT (293) and
PPL (192) wires to the Defogger Timer-Relay
for an open (see schematic). If OK, do Test E.
• If the test lamp bulb shows full brilliance at
both ends of the grid, check the braided wire
for an open to ground (see schematic).
• If the test lamp suddenly lights as it is moved
along the grid, a break in the continuity of the
grid line exists. Refer to the GM Body Service
Manual for grid line repair procedure.
E: DEFOGGER LAMP T E S T
(Continued from previous column)
Connect: TEST LAMP
At: REAR DEFOGGER CONNECTOR C302
(Connected)
Conditions:
• Ignition Switch: RUN
• Defogger Control Switch: ON
Connect
Between
Correct Result For Diagnosis
C302 (PPL) &
Ground
Lamp lights Seel
C302 (PPL) &
G303 Braided
Wire
Lamp lights See 2
• If all the results are correct, refer to the
GM Body Service Manual, Section 2, for
grid line repair.
1. Do Test B.
2. Check the braided wire for an open. Check
that ground G303 is clean and tight (see
schematic).
(Continued in next column)
CIRCUIT OPERATION
With the Ignition Switch in RUN, voltage is
applied to the Defogger Control.
When the Defogger Control Switch is pressed
ON, voltage is then applied to the Defogger
Timer-Relay. The contact closes, which pro-
vides voltage to the ON Indicator and the Rear
Defogger. The rear window will become warm
to remove the fog from the surface of the win-
dow.
The contact in the Defogger Timer-Relay will
stay closed until the Defogger Control Switch is
turned OFF, or until the timer cycle is complete.
The first time the Defogger Control Switch is
pushed in, the Defogger Timer-Relay will allow
the Rear Defogger to operate for approximately
10 minutes. Each time after the Defogger Con-
trol Switch is pushed in, the Defogger Timer-
Relay will reset to operate for approximately 5
minutes. The Defogger Timer-Relay will reset
to 10 minutes when the Ignition Switch is
turned OFF and then back to the RUN position.
The timer also shuts off at any time when the
Defogger Control On-Off Switch is depressed
OFF. In order to reset the Defogger Timer-
Relay for the initial 10 minute time interval, the
Ignition Switch must be turned OFF and then
back to the RUN position before activating the
Rear Defogger.