Rear Window Defogger Inoperative C68

Battery positive voltage is supplied through the BATT 1 fuse in the underhood fuse block to the rear defog relay switched input. When the rear defog switch button is pressed, the body control module (BCM) energizes the rear defog relay by providing a B+ to the control circuit of the rear defog relay. This allows battery positive voltage from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger grid. The HVAC control module houses the rear defog switch and also illuminates the rear defog indicator on the switch button, upon this request. Ground for the rear window defogger grid is provided by G301 for the Sedan or G302 for the Extended Sedan.

When you start the engine and press the rear defog switch button, the defog cycle lasts for 10 minutes. Further operation will result in 5 minute defog cycles.

The rear defogger feature will not time out if vehicle speed is above 48 km/h (30 mph).

If battery voltage is low, the rear defogger feature will be disabled.

Schematic Reference

Defogger Schematics

Connector End View Reference

Window Systems Connector End Views

Description and Operation

Rear Window Defogger Description and Operation

Electrical Information Reference

Scan Tool Reference

1. Ignition ON, observe the Defog Indicator while pressing the Defog Switch. The indicator should turn ON and OFF.

⇒	If the indicator does not change between the commanded states, replace HVAC control module.

2. Command the rear window defogger ON and OFF with the scan tool. The rear window defogger should turn ON and OFF when changing between the commanded states.

1. Ignition OFF, disconnect the R/WDO DEFOG relay.
2. Test for less than 1 ohm of resistance between the relay coil ground circuit and ground.

⇒	If greater than the specified range, test the relay coil ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp does not illuminate between the relay controlled output circuit and ground.

⇒	If the test lamp illuminates, test the relay controlled output circuit for a short to voltage.

4. Verify that a test lamp illuminates between the relay switch side B+ circuit and ground.

⇒	If the test lamp does not illuminate, test the relay switch side B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the switch side circuit fuse is open, test the relay controlled output circuit for a short to ground.

5. Disconnect the harness connector at the rear window defogger grid.
6. Ignition OFF, test for less than 1 ohm of resistance between the rear window defogger grid ground circuit and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the rear window defogger grid.
8. Ignition ON, connect a 30-amp fused jumper wire between the relay switch B+ circuit and the relay controlled output circuit. Verify the rear window defogger grid is activated.

⇒	If the rear window defogger grid does not activate, test the relay controlled output circuit for an open/high resistance. If the circuit tests normal, test or repair the rear window defogger grid.

9. Connect a test lamp between the rear defogger control circuit and the relay coil ground circuit.
10. Command the R/WDO DEFOG relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the rear defogger control circuit for a short to voltage. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the rear defogger control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

11. If all circuits test normal, test or replace the R/WDO DEFOG relay.

Relay Test

1. Ignition OFF, disconnect the R/WDO DEFOG relay.
2. Test for 60-180 ohms of resistance between terminals 85 and 86.

⇒	If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If not the specified value, replace the relay.

4. Install a 25-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of resistance between terminals 30 and 87.

⇒	If greater than the specified range, replace the relay

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Rear Window Defogger Inoperative C60

Battery positive voltage is supplied through the BATT 1 fuse in the underhood fuse block to the rear defog relay switched input. When the rear defog switch button is pressed, the body control module (BCM) energizes the rear defog relay by providing a B+ to the control circuit of the rear defog relay. This allows battery positive voltage from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger grid. The HVAC control module houses the rear defog switch and also illuminates the rear defog indicator on the switch button, upon this request. Ground for the rear window defogger grid is provided by G301 for the Sedan or G302 for the Extended Sedan.

When you start the engine and press the rear defog switch button, the defog cycle lasts for 10 minutes. Further operation will result in 5 minute defog cycles.

The rear defogger feature will not time out if vehicle speed is above 48 km/h (30 mph).

If battery voltage is low, the rear defogger feature will be disabled.

Schematic Reference

Defogger Schematics

Connector End View Reference

Window Systems Connector End Views

Description and Operation

Rear Window Defogger Description and Operation

Electrical Information Reference

Scan Tool Reference

1. Ignition ON, observe the scan tool Manual HVAC Rear Defog Sw parameter while pressing the Defog Switch. The reading should change between ON and OFF.

⇒	If the reading does not change between the commanded states, refer to HVAC Control Module Malfunction.

2. Command the rear window defogger ON and OFF with the scan tool. The rear window defogger and Defog Indicator should turn ON and OFF when changing between the commanded states.

⇒	If the rear window defogger does not turn ON and OFF when changing between the commanded states, refer to Rear Defogger Malfunction.

⇒	If the Defog Indicator does not illuminate or continuously illuminates, refer to Rear Defogger Indicator Malfunction.

HVAC Control Module Malfunction

1. Ignition OFF, disconnect the harness connector C1 at the HVAC control module.
2. Ignition OFF, test for less than 1 ohm of resistance between the ground circuit terminal B5 and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the scan tool Manual HVAC Rear Defog Sw parameter is OFF.

⇒	If not the specified value, test the signal circuit terminal A8 for a short to ground. If the circuit tests normal, replace the BCM.

4. Install a 3-amp fused jumper wire between the signal circuit terminal A8 and ground. Verify the scan tool Manual HVAC Rear Defog Sw parameter is ON.

⇒	If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, test or replace the HVAC control module.

Rear Defog Indicator Malfunction

1. Ignition OFF, disconnect the harness connector C1 at the HVAC control module.
2. Disconnect the R/WDO DEFOG relay.
3. Connect a test lamp between the control circuit terminal B8 and ground.
4. Ignition ON, command the Rear Defog Relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

5. If all circuits test normal, test or replace the HVAC control module.

Rear Defogger Malfunction

1. Ignition OFF, disconnect the R/WDO DEFOG relay.
2. Ignition OFF, test for less than 1 ohm of resistance between the relay coil ground circuit and ground.

⇒	If greater than the specified range, test the relay coil ground circuit for an open/high resistance.

3. Ignition ON, verify that a test lamp does not illuminate between the relay controlled output circuit and ground.

⇒	If the test lamp illuminates, test the relay controlled output circuit for a short to voltage.

4. Verify that a test lamp illuminates between the relay switch side B+ circuit and ground.

⇒	If the test lamp does not illuminate, test the relay switch B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the fuse is open, test the relay controlled output circuit for a short to ground.

5. Ignition OFF, disconnect the harness connector at the rear window defogger grid.
6. Ignition OFF, test for less than 1 ohm of resistance between the rear window defogger grid ground circuit terminal A and ground

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector C1 at the rear window defogger grid.
8. Ignition ON, connect a 30-amp fused jumper wire between the relay switch B+ circuit and the relay controlled output circuit. Verify the rear window defogger grid is activated.

⇒	If the rear window defogger grid does not activate, test the relay controlled output circuit for an open/high resistance. If the circuit tests normal, test or replace the rear window defogger grid.

9. Connect a test lamp between the rear defogger control circuit and the relay coil ground circuit.
10. Command the rear defog relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the rear defogger control circuit for a short to voltage. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the rear defogger control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

11. If all circuits test normal, test or replace the R/WDO DEFOG relay.

HVAC Control Module

1. Ignition OFF, disconnect the harness connector at the HVAC control module.
2. Test for infinite resistance between the signal terminal A8 and the ground circuit terminal B5 with the switch in the open position.
3. Test for less than 2 ohms between the signal terminal A8 and the ground circuit terminal B5 with the switch in the closed position.

⇒	If not the specified value, replace the HVAC control module.

Defog Indicator

1. Ignition OFF, disconnect the harness at the HVAC control module.
2. Install a 5-amp fused jumper wire between circuit terminal B8 and 12 volts. Install a jumper wire between the ground circuit terminal B5 and ground. Verify the Defog Indicator illuminates.

⇒	If the Defog Indicator does not illuminate, replace the HVAC control module.

Relay Test

1. Ignition OFF, disconnect the R/WDO DEFOG relay.
2. Test for 60-180 ohms of resistance between terminals 85 and 86.

⇒	If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If not the specified value, replace the relay.

4. Install a 25-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of resistance between terminals 30 and 87.

⇒	If greater than the specified range, replace the relay

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for BCM replacement, setup and programming