Pinpoint Test E: the Defrost System Is Inoperative
Glass, Frames and Mechanisms
Pinpoint Tests
Pinpoint Test E: The Defrost System is Inoperative
Refer to Wiring Diagram Set 56, Heated Window for schematic and connector information. Diagrams By Number
Normal Operation
The rear window defrost system is controlled by the HVAC module. The engine must be running for the defrost system to operate. When the rear window defrost button is pressed, the HVAC module provides a ground for the rear window defrost relay coil through circuit 688 (GY/LB). The rear window defrost relay coil is energized, providing battery voltage to the antenna module on circuit 186 (BN/LB). The antenna module then supplies voltage and ground to the rear window defrost grid.
This pinpoint test is intended to diagnose the following:
- Fuse(s)
- Wiring, terminals or connectors
- Rear window defrost relay
- Antenna module
- Rear window defrost grid
- HVAC module
PINPOINT TEST E: THE DEFROST SYSTEM IS INOPERATIVE
NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
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E1 CHECK THE SIGNAL INPUT
- Disconnect: Rear Window Defrost Relay.
- Start the engine.
- Press the rear window defrost switch to the ON position.
- Measure the resistance between rear window defrost relay pin 85, circuit 688 (GY/LB), harness side and ground.
- Is the resistance less than 70 ohms?
Yes
GO to E4.
No
GO to E2.
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E2 CHECK CIRCUIT 688 (GY/LB) FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: HVAC module C228b.
- Ignition ON.
- Measure the voltage at rear window defrost relay pin 85, circuit 688 (GY/LB), harness side and ground.
- Is any voltage indicated?
Yes
REPAIR the circuit. TEST the system for normal operation.
No
GO to E3.
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E3 CHECK CIRCUIT 688 (GY/LB) FOR AN OPEN
- Ignition OFF.
- Measure the resistance between rear window defrost relay pin 85, circuit 688 (GY/LB), harness side and HVAC module C228b-20, circuit 688 (GY/LB), harness side.
- Is the resistance less than 5 ohms?
Yes
INSTALL a new HVAC module. TEST the system for normal operation.
No
REPAIR the circuit. TEST the system for normal operation.
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E4 CHECK CIRCUIT 185 (BK) FOR AN OPEN
- Measure the voltage between rear window defrost relay pin 86, circuit 185 (BK), harness side and ground; and between rear window defrost relay pin 30, circuit 185 (BK), harness side and ground.
- Are the voltages greater than 10 volts?
Yes
GO to E5.
No
VERIFY the Battery Junction Box (BJB) fuse 107 (40A) is OK. If OK, REPAIR the circuit in question. TEST the system for normal operation. If not OK, REFER to Wiring Diagrams to identify the possible causes of the circuit short. REPAIR the circuit. TEST the system for normal operation.
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E5 CHECK THE RELAY OUTPUT TO THE HEATED REAR WINDOW GRID
- Ignition OFF.
- Connect: Rear Window Defrost Relay.
- Disconnect: Rear Window Defrost Grid Connector.
- Start the engine.
- Press the rear window defrost switch to the ON position.
- Measure the voltage between the rear window defrost grid connector harness side and ground.
- Is the voltage greater than 10 volts?
Yes
GO to E8.
No
GO to E6.
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E6 CHECK THE RELAY OUTPUT TO THE ANTENNA MODULE
- Ignition OFF.
- Disconnect: Antenna Module C4221.
- Start the engine.
- Press the rear window defrost switch to the ON position.
- Measure the voltage between antenna module C4221-1, circuit 186 (BN/LB), harness side and ground.
- Is the voltage greater than 10 volts?
Yes
INSTALL a new antenna module. TEST the system for normal operation.
No
GO to E7.
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E7 CHECK CIRCUIT 186 (BN/LB) FOR AN OPEN OR SHORT TO GROUND
- Ignition OFF.
- Disconnect: Rear Window Defrost Relay.
- Measure the resistance between antenna module C4221-1, circuit 186 (BN/LB), harness side and rear window defrost relay pin 87, circuit 186 (BN/LB), harness side; and between antenna module C4221-1, circuit 186 (BN/LB), harness side and ground.
- Is the resistance less than 5 ohms between the antenna module and the rear window defrost relay; and greater than 10,000 ohms between the antenna module and ground?
Yes
INSTALL a new rear window defrost relay. TEST the system for normal operation.
No
REPAIR the circuit. TEST the system for normal operation.
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E8 CHECK THE GROUND FOR THE HEATED REAR WINDOW GRID
NOTE: Make sure the accessory delay has timed out.
- Ignition OFF.
- Disconnect: Rear Window Defrost Grid Ground Connector.
- Measure the resistance between the rear window defrost grid ground connector, harness side and ground.
- Is the resistance less than 5 ohms?
Yes
CARRY OUT the Grid Wire Test. REPAIR the Rear Window Defrost Grid. REFER to Window Grid Wire Repair Window Grid Wire Repair. TEST the system for normal operation.
No
INSTALL a new antenna module. TEST the system for normal operation.
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