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Test Description

WARNING: This page is about a different car, the 2004 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 3:  This step tests for voltage at the defog grid. If the voltage signal is present the malfunction is in the grid.
  1. 4:  If the relay can be commanded ON then the malfunction is in the message sent from the HVAC module.
  1. 7:  This step completely test all of the output wiring of the circuit. If no malfunction is fond in this step then the relay is the cause of the concern. The BCM has integral diagnostic capabilities to analyze the control side of the relay. If no code is set for the control circuit and the relay can be commanded ON and OFF then the relay is at fault.
Defogger Inoperative - Rear Window

Step Action Yes No
Schematic Reference: Defogger Schematics 
Connector End View Reference: Stationary Windows Connector End Views 
DEFINITION: The rear window defogger is completely inoperative. No part of the rear window is heating.
1 Did you perform the Defogger Diagnostic System Check? Go to Step 2  Go to Diagnostic System Check - Defogger 
2
IMPORTANT: Make sure that the park or head lights are turned OFF. The backlighting will effect the illumination of the rear window defogger indicator.
  1. Start the engine.
  2. Depress the rear window defogger switch.
  3. Observe the rear window defogger indicator on the HVAC Control Module.
Does the rear window defogger indicator illuminate?		 Go to Step 3  Go to Step 5 
3  Connect a test lamp between the left side of the rear window defogger grid and the right side of the rear window defogger grid.
Does the test lamp illuminate?		 Go to Defogger Grid Lines Diagnosis  Go to Step 4 
4 
  1. Using the scan tool command the Rear Defog Relay ON.
  2. Using the test lamp, test between the left side of the rear window defogger grid and the right side of the rear window defogger grid.
Does the test lamp illuminate?		 Go to Step 5  Go to Step 7 
5 Test for poor connections and proper terminal tension at the HVAC control modules harness connector.
Did you find and correct the condition?		 Go to Step 9  Go to Step 6 
6 Replace the HVAC control module. Refer to HVAC Control Assembly Replacement in HVAC Systems Manual.
Did you complete the replacement?		 Go to Step 9  -
7 
  1. Turn OFF the ignition.
  2. Disconnect the REAR DEFOG relay.
  3. Test for an open in the positive feed circuit between the Rear Window Defogger Grid and the REAR DEFOG relay socket. Refer to Circuit Testing in Wiring Systems.
  4. Test for an open in the Rear Window Defogger Grid ground circuit. Refer to Circuit Testing in Wiring Systems.
  5. Test the battery voltage feed circuit of the REAR DEFOG relay. Refer to Circuit Testing in Wiring Systems.
Did you find and correct the condition?		 Go to Step 9  Go to Step 8 
8 Replace the REAR DEFOG relay.
Did you complete the replacement?		 Go to Step 9  -
9 Reconnect all disconnected connectors and devices.
Operate the system in order to verify the repair.
Did you correct the condition?		 System OK Go to Step 2 
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