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Rear Window Defogger Grid Inoperative

Possible Causes are:

  1. Using the DRBIII(R), read the Body Computer DTC's. Are there any Rear Defogger Relay DTC's present? If yes, see DIAGNOSTIC TROUBLE CODE IDENTIFICATION  table in RETRIEVING & CLEARING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS. If no, go to next step.
  2. Toggle the Rear Defogger switch and observe the indicator. Does the indicator toggle on and off when the switch is pressed? If yes, go to next step. If no, go to step  5 .
  3. Turn the ignition and all lights off. Open the liftgate. Measure the resistance between ground and the Rear Window Defogger Ground circuit. Is the resistance less than 5 ohms? If yes, go to next step. If no, repair the open Rear Window Defogger Ground circuit. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS.
  4. Turn ignition on. Turn the Rear Window Defogger on. Measure the voltage between the Rear Window Defogger Relay Output circuit at the defogger grid on the rear window to ground. Is the voltage more than 12 volts? If yes, repair the open in the Rear Window Defogger Grid. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS. If no, repair the open Rear Window Defogger Relay Output circuit. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS.
  5. Turn ignition on. Using the DRBIII(R), read the R DEFOG SWITCH Input/Output display. Toggle the Rear Window Defogger Switch on and off and observe the DRBIII(R). Does the DRBIII(R) show that the Rear Defog Switch is toggling on and off? If yes, go to next step. If no, go to step  12 .
  6. Remove and inspect the PDC fuse No. 2. Is the PDC fuse No. 2 open? If yes, go to next step. If no, go to step  9 .
  7. Remove the Rear Window Defogger Relay from the Junction Block. Measure the resistance of the Rear Window Defogger Relay coil in cavities No. 85 and 86. Is the resistance 50-100 ohms? If yes, go to next step. If no, replace the rear window defogger relay and replace PDC fuse No. 2, if necessary. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS.
  8. Disconnect the Rear Window Defogger connector at the rear window grid. Remove the Rear Window Defogger Relay from the Junction Block. Measure the resistance between ground and the Rear Window Defogger Relay Output circuit at the Rear Window Defogger connector. Is the resistance less than 5 ohms? If yes, repair the Rear Window Defogger Relay Output circuit for a short to ground. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS. If no, replace the PDC fuse No. 2. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS.
  9. Lower the Junction Block and remove the Rear Window Defogger Relay. Turn ignition on. Measure the voltage of the Fused B (+) circuit in the Rear Window Defogger Relay connector. Is the voltage more than 10 volts? If yes, go to next step. If no, repair the open Fused B (+) circuit from PDC fuse No. 2. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS.
  10. Lower the Junction Block and remove the Rear Window Defogger Relay. Install a known-good relay in the Rear Window Defogger Relay connector. Turn ignition on. Check the Rear Window Defogger for proper operation. Does the system operate properly now? If yes, replace the original Rear Window Defogger Relay. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS. If no, go to next step.
  11. Using the DRBIII(R), actuate the R DEFOG RELAY. Using a 12-volt test light connected to ground, back probe the Rear Window Defogger Relay Output circuit in the Junction Block C1 connected. Does the test light flash on and off when the relay is actuated? If yes, the condition that caused this symptom is currently not present. Inspect the related wiring harness for a possible intermittent condition. Look for any chafed, pierced, pinched or partially broken wires. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS. If no, replace the junction block. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS.
  12. Turn ignition off. Disconnect the BCM C2 connector. Disconnect the Temperature Control C1 connector. Check connectors, clean or repair as necessary. Measure the resistance of the Rear Window Defogger Switch Sense circuit between the BCM connector and the AZC connector. Is the resistance less than 5 ohms? If yes, go to next step. If no, repair the open Rear Window Defogger Switch Sense circuit. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS.
  13. Turn ignition off. Disconnect the BCM C2 connector. Disconnect the Temperature Control C1 connector. Measure the resistance between ground and the Rear Window Defogger Switch Sense circuit. Is the resistance less than 5 ohms? If yes, repair the Rear Window Defogger Switch Sense circuit for a short to ground. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS. If no, go to next step.
  14. Turn ignition off. Disconnect the BCM C2 connector. Disconnect the Temperature Control C1 connector. Check connectors, clean and repair as necessary. Turn ignition on. Measure the voltage between the Rear Window Defogger Switch Sense circuit and ground. Is there any voltage present? If yes, repair the Rear Window Switch Sense circuit for a short to voltage. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS. If no, go to next step.
  15. Ensure the BCM is connected before proceeding. Turn ignition off. Disconnect the Temperature Control C1 connector. Connect a jumper wire between the Rear Window Defogger Switch Sense circuit in the Temperature Control connector to ground. Turn ignition on. Using the DRBIII(R), read the R DEFOG SWITCH status. Does the DRBIII(R) display R DEFOG SWITCH: CLOSED? If yes, replace the Automatic Zone Control Module. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS. If no, replace the Body Control Module. Perform BODY VERIFICATION TEST VER 1  under VERIFICATION TESTS.
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