When the rear window defogger switch is activated, the HVAC control module energizes the rear defog relay by providing voltage to the rear defog relay control circuit. When the rear defog relay coil is energized, the switch contacts of the rear defog relay close allowing battery voltage to flow through the closed switch contacts of the relay, through the F28UA fuse and to the rear window defogger grid.

Schematic Reference

Defogger Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Rear Window Defogger Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, observe the scan tool Rear Defogger Switch parameter while pressing the rear window defogger switch, the parameter should change from Inactive to Active.

⇒	If the value does not change, replace the K33 HVAC control module.

2. Observe the operation of the rear window defogger indicator while pressing the rear window defogger switch. The indicator should turn ON or OFF each time the rear window defogger switch is pressed.

⇒	If the indicator does not turn ON or OFF with each switch press, replace the K33 HVAC control module.

3. Command the Rear Defog ON and OFF with a scan tool, the E18 rear window defogger grid should turn ON or OFF while changing between the commanded states.

1. Ignition OFF, disconnect the X2 harness connector at the X50A underhood fuse block.
2. Connect a test lamp between the control circuit terminal 61 and ground..
3. Ignition ON, command the Rear Defog 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 K33 HVAC control module.

⇒	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 K33 HVAC control module.

4. Ignition OFF, connect the X2 harness connector at the X50A underhood fuse block.
5. Disconnect the X1 and X2 harness connectors at the E18 rear window defogger grid.
6. Test for less than 5 ohms between the ground circuit terminal 1 and ground.

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

7. Connect a test lamp between the control circuit terminal 1 and ground.
8. Ignition ON, command the Rear Defog 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 X50A underhood fuse block.

⇒	If the test lamp is always OFF and the circuit fuse is open, test the control circuit for a short to ground. If the circuit tests normal, test or replace the E18 rear window defogger grid.

⇒	If the test lamp is always OFF and the circuit fuse is good, test the control circuit for an open/high resistance. If the circuit tests normal, replace the X50A underhood fuse block.

9. If all circuits test normal, test or replace the E18 rear window defogger grid.

Rear Window Defogger Grid Test

1. Ignition ON, turn on the E18 rear window defogger grid.
2. Verify that a test lamp illuminates between each rear window defogger grid line and ground. The test lamp should be off when testing at the ground side of the grid and get brighter as the test lamp moves closer to the voltage supply side of the grid. The test lamp should be dim when testing each grid line in the middle.

⇒	If the test lamp remains bright at the middle of the grid line, test for an open between the test point and the ground side of the grid.

⇒	If the test lamp remains off at the middle of the grid line, test for an open between the test point and the voltage supply side of the grid

Relay Test

1. Ignition OFF, disconnect the KR5 Rear Window Defogger relay.
2. Test for 60-180 ohms between terminals 85 and 86.

⇒	If not within the specified range, replace the KR5 Rear Window Defogger 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 KR5 Rear Window Defogger relay.

4. Install a 30A fused jumper wire between relay terminal 85 and 12V. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms of between terminals 30 and 87.

⇒	If greater than the specified range, replace the KR5 Rear Window Defogger relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.