Circuit/System Testing

HVAC Rear Defog Switch Malfunction

1. Ignition OFF, disconnect the harness connector C2 at the HVAC Control Assembly.
2. Test for less than 1 ohm of resistance between the ground circuit terminal K 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 J for a short to ground. If the circuit tests normal, replace the BCM
4. Install a 3-A fused jumper wire between the signal circuit terminal J 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 Assembly.

Rear Defog Indicator Malfunction

1. Ignition OFF, disconnect the harness connector C2 at the HVAC Control Assembly.
2. Disconnect the REAR DEFOG relay.
3. Connect a test lamp between the control circuit terminal G 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 Assembly.

Rear Defogger Malfunction

1. Ignition OFF, disconnect the REAR DEFOG relay.
2. Test for less than 1 ohm of resistance between the relay coil ground circuit V10 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 U10 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 B+ circuit V12 and ground.
   • If the test lamp does not illuminate, test the relay switch B+ circuit V12 for a short to ground or an open/high resistance. If the circuit tests normal and the RR DEFOG fuse is open, test the relay controlled output circuit U10 for a short to ground.
5. Ignition OFF, disconnect the harness connector at the Rear Window Defogger Grid.
6. 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 at the Rear Window Defogger Grid.
8. Ignition ON, connect a 30 amp fused jumper wire between the relay switch B+ circuit V12 and the relay controlled output circuit U10. Verify the Rear Window Defogger Grid is activated.
   • If the Rear Window Defogger Grid does not activate, test the relay controlled output circuit U10 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 U12 and the relay coil ground circuit V10.
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 U12 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 U12 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 REAR DEFOG relay.