1982-1992 Pontiac Firebird Service & Repair Manual

DEFOGGER - REAR WINDOW 1990 ACCESSORIES & SAFETY EQUIPMENT General Motors Defogger - Rear Window DESCRIPTION & OPERATION DESCRIPTION The heated rear window defogger uses a heating grid baked to the inside of the rear window. Window heat is controlled by a control switch and a timer/relay. The timer/relay is located in the accessory relay panel. When defogger is operating, indicator light will glow to show system is on. Current feed to defogger is through a circuit breaker and power to control switch is through a fuse in the fuse block. OPERATION Voltage is applied to the rear defogger through the defogger relay. With the ignition switch in RUN position, voltage is applied to one side of defogger relay coil. When rear defogger ON/OFF switch is activated, a ground signal is sent from heater-A/C control to the Central Control Module (CCM). Upon receiving this ground signal, and only if the engine is running, the CCM then energizes the defogger relay by grounding the other side of the defogger relay coil. When energized, the normally open contacts in the defogger relay close, applying voltage to heat the rear defogger. The CCM will energize the defogger relay for 10 minutes during the first activation of the rear defogger after ignition on, engine running, and for 5 minutes each additional activation. This timing process will reset at each ignition cycle. TROUBLE SHOOTING Before performing system test, check the following:  Check the SEATS circuit breaker by operating seats and power door locks.  Check body fuse by operating courtesy lights.  Check ignition fuse by operating back-up lights.  Check fuse to gauges by observing fuel gauge operation. If components appear to be in good condition, proceed to GRID TEST , SYSTEM TEST, and the appropriate component TESTS A:, B:, C:, D: or E: (as applicable). TESTING GRID TEST 1. Start engine and turn rear defogger control switch on. Using a test light connected to ground, lightly touch each grid line. If test light shows full brilliance at both ends of all grid lines, check for loose ground wire. Test light brilliance will gradually change as test light probe is moved from left bus bar to right bus bar. 2. Contact each grid line a few inches on either side of glass center line to eliminate the possibility of missing a break in grid line. If a problem on a grid line is detected, place test light probe on that grid line at left bus bar and move probe toward right bus bar until light goes out. This will indicate a break in continuity of grid line. See Fig. 1 . 1990 Chevrolet Camaro RS DEFOGGER - REAR WINDOW 1990 ACCESSORIES & SAFETY EQUIPMENT General Motors Defogger - Rear Window 1990 Chevrolet Camaro RS DEFOGGER - REAR WINDOW 1990 ACCESSORIES & SAFETY EQUIPMENT General Motors Defogger - Rear Window

1990 Chevrolet Camaro RS DEFOGGER - REAR WINDOW 1990 ACCESSORIES & SAFETY EQUIPMENT General Motors Defogger - Rear Window

Fig. 1: Grid Brilliance Test Patterns Courtesy of GENERAL MOTORS CORP. SYSTEM TEST "F" BODY SYSTEM TEST TEST A: TIMER RELAY INPUT VOLTAGE TEST - "F" BODY Measure: Voltage at defogger timer-relay connector (connected) with ignition switch in RUN position. TEST A: TIMER RELAY INPUT VOLTAGE TEST (1) TEST B: REAR DEFOGGER RELAY TEST - "F" BODY Measure: Voltage at rear defogger control connector (connected) with ignition switch in RUN position, rear defogger switch ON (HOLD). TEST B: REAR DEFOGGER RELAY TEST (1) Action Normal Result Go To Test: W/ ignition on, turn rear defogger switch ON Button returns to "rest" & ON indicator in center of rear defogger control lights Do TEST A . " The rear window becomes warm Do TEST D . & TEST E . " The ON indicator & rear defogger turn off after approximately 10 minutes Replace rear defogger control Depress rear defogger switch again The ON indicator & rear rear defogger operate for approximately 5 minutes Replace rear defogger control Measure Between Correct Voltage For Diagnosis ORG/BLK & GND Battery (2) PNK/BLK & GND Battery (3) (1) If all results are correct, go to TEST B: REAR DEFOGGER RELAY TEST . (2) Check ORG/BLK wire for an open. If okay, check power accessory circuit breaker. (3) Check PNK/BLK wire for an open. If okay, check the gauges fuse. Connect Between Correct Voltage For Diagnosis LT BLU & GND Battery (2) DK BLU & LT BLU Battery (3) PPL/WHT & GND Battery (4) PPL/WHT & GND (2) No Voltage (5) 1990 Chevrolet Camaro RS DEFOGGER - REAR WINDOW 1990 ACCESSORIES & SAFETY EQUIPMENT General Motors Defogger - Rear Window

TEST C: DEFOGGER CONTROL VOLTAGE TEST - "F" BODY Measure: Voltage at defogger control connector (connected) with ignition switch in RUN position and rear defogger switch ON (HOLD) and headlight switch in PARK (maximum brightness) position. TEST C: DEFOGGER CONTROL VOLTAGE TEST (1) TEST D: GRID TEST - "F" BODY See GRID TEST under TESTING at the beginning of this article. TEST E: DEFOGGER LIGHT TEST - "F" BODY Measure: Voltage at left and right hatch support arm (connected) with ignition switch in RUN position, defogger switch ON. TEST E: REAR DEFOGGER TEST (1) (1) If voltage is correct, perform TEST D . (2) Switch OFF (HOLD). (3) Check LT BLU wire for an open. If wire is okay, perform TEST C . (4) Check BLK for an open. Ensure ground is clean and tight. (5) Replace defogger timer relay. Connect Between Correct Voltage For Diagnosis PNK/BLK & GND Battery (2) LT BLU & GND Battery (3) PPL/WHT & GND Battery (4) GRY & GND Battery (5) GRY & BLK Battery (6) (1) If all voltages are correct, and defogger still does not operate properly, perform TEST D . (2) Check PNK/BLK wire for an open. If wire is okay, check gauges fuse. (3) Replace defogger control. (4) Check the PPL/WHT wire for an open. If wire is okay, perform TEST B . (5) Check INST LP fuse. Check the GRY wire for an open. (6) Check BLK wire for an open. Check that ground is clean and tight. Replace panel light if wire and ground are okay. Measure Between Correct Voltage For Diagnosis LH Arm & GND Battery (2) 1990 Chevrolet Camaro RS DEFOGGER - REAR WINDOW 1990 ACCESSORIES & SAFETY EQUIPMENT General Motors Defogger - Rear Window

LH Arm & RH Arm Battery (3) (1) If all voltages are correct, repair grid. (2) Perform Test B. (3) Check the BLK wire for an open. Make sure the ground is clean and tight. 1990 Chevrolet Camaro RS DEFOGGER - REAR WINDOW 1990 ACCESSORIES & SAFETY EQUIPMENT General Motors Defogger - Rear Window

1982-1992 Pontiac Firebird Service & Repair Manual

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