Spark

Rear Window Defogger Malfunction

The rear window demister is controlled by the rear demister relay through a high side drive control circuit. Battery voltage is supplied to the switch side of the relay at all times and when the relay is energised battery voltage is supplied to the rear window demister control circuit. The rear demister relay is controlled by the rear window demister switch through a low side drive control circuit. Ignition voltage is supplied to the relay coil and when the rear demister switch is pressed the relay control circuit is grounded and the relay will be energised.

Schematic Reference

Defogger Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Rear Window Defogger Description and Operation

Electrical Information Reference

1. Ignition OFF, disconnect the rear demister relay.
2. Ignition ON, verify that a test lamp does not illuminate between the rear window demister control circuit terminal 87 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the ignition circuit terminal 85 and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test or replace rear demister relay.

4. Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the rear window demister control circuit terminal 87 for a short circuit to ground.

5. Disconnect the X2 wiring harness plug at the rear window demister grid.
6. Test for less than 1 Ω between the demister grid ground circuit terminal 1 and ground.

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

7. Connect the X2 wiring harness plug at the rear window demister grid.
8. Disconnect the X2 wiring harness plug at the HVAC control switch assembly.
9. Test for less than 1 Ω between the demister switch ground circuit terminal 2 and ground.

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

10. Connect the X2 wiring harness plug at the HVAC control switch assembly.
11. Connect a 20 A fused jumper wire between the B+ circuit terminal 30 and the rear window demister control circuit terminal 87. Verify the rear window demister is activated.

⇒	If the rear window demister does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, repair or replace the rear window demister grid.

12. Connect a test lamp between the ignition circuit terminal 85 and the relay control circuit terminal 86.
13. Cycle the rear window demister switch ON and OFF. 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 ground. If the circuit tests normal, replace the rear window demister switch.

⇒	If the test lamp is always OFF, test the control circuit for an open/high resistance. If the circuit tests normal, replace the rear window demister switch.

14. If all circuits test normal, test or replace the rear demister relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.