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Rear Window Defogger Malfunction




Rear Window Defogger Malfunction

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.

* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information






Circuit/System Description

When the HVAC control module receives a rear window defog request from the Radio/HVAC controls, the HVAC control module will supply voltage to the relay coil. Battery positive voltage is supplied at all times to the relay switched input and the relay coil is always grounded. This allows battery positive voltage from the relay switched input to flow through the switch contacts and out the relay switched output to the rear window defogger grid.

Diagnostic Aids

Rear window defogger indicator will still function when the switch is pressed but any of the following conditions may cause the rear window defogger not to function:

* Ambient temperature at the HVAC control module must be less than 10°C (50°F).

* System voltage is out of range.

* A DTC is set that disables rear window defogger functionality.

Reference Information

Schematic Reference

Defogger Schematics Electrical Diagrams

Connector End View Reference

Component Connector End Views Hybrid/EV Battery Pack X1

Description and Operation

Rear Window Defogger Description and Operation Description and Operation

Electrical Information Reference

* Circuit Testing Circuit Testing

* Connector Repairs Connector Repairs

* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections

* Wiring Repairs Wiring Repairs

Scan Tool Reference

Control Module References Programming and Relearning for scan tool information

Circuit/System Verification

1. Vehicle ON.

2. Verify the scan tool Rear Defogger Switch parameter changes between On and Off when pressing the rear window defogger switch.

• If the parameter does not change between On and Off
Replace the A20 Radio/HVAC controls.

• If the parameter changes between On and Off

3. Verify the rear defogger indicator turns ON and OFF when pressing the rear window defogger switch.

• If the rear defogger indicator does not turn ON and OFF
Replace the A20 Radio/HVAC controls.

• If the rear defogger indicator turns ON and OFF

4. Verify the upper rear defogger grid and the lower rear defogger grid turns ON and OFF when commanding the rear window defogger ON and OFF with a scan tool.

• If only the upper rear window defogger grid does not turn ON and OFF
Refer to Circuit/System Testing - Upper Defogger Grid Inoperative

• If only the lower rear window defogger grid does not turn ON and OFF
Refer to Circuit/System Testing - Lower Defogger Grid Inoperative

• If both upper and lower rear window defogger grids do not turn ON and OFF
Refer to Circuit/System Testing - Rear Window Defogger System Inoperative

• If both the upper and lower rear window defogger grids turns ON and OFF

5. All OK.

Circuit/System Testing

Upper Defogger Grid Inoperative

1. Vehicle OFF, disconnect the KR5 rear defogger relay. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 ohms between the ground circuit terminal 40 and ground.

• If 10 ohms or greater

1. Vehicle OFF.

2. Test for less than 2 ohms in the ground circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, repair the open/high resistance in the ground connection.

• If less than 10 ohms

3. Verify that a test lamp does not illuminate between the control circuit terminal 41 and ground.

• If the test lamp illuminates
Repair the short to voltage on the control circuit

• If the test lamp does not illuminate

4. Vehicle OFF, disconnect the X2 harness connector at the E18A rear defogger grid - upper. It may take up to 2 minutes for all vehicle systems to power down.

5. Test for less than 10 ohms between the ground circuit terminal 1 and ground.

• If 10 ohms or greater

1. Vehicle OFF.

2. Test for less than 2 ohms in the ground circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, repair the open/high resistance in the ground connection.

• If less than 10 ohms

6. Connect the X2 harness connector at the E18A rear defogger grid - upper.

7. Vehicle in Service Mode, connect a 40 A fused jumper wire between the B+ circuit terminal 43 and the control circuit terminal 42.

8. Verify the E18A rear defogger grid - upper is activated.

• If the E18A rear defogger grid - upper does not activate

1. Vehicle OFF, disconnect the X1 harness connector at the E18A rear defogger grid - upper.

2. Test for infinite resistance between the control circuit and ground.

• If less than infinite resistance, repair the short to ground on the circuit.

• If infinite resistance

3. Test for less than 2 ohms in the control circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, replace the E18A rear defogger grid - upper.

• If the E18A rear defogger grid - upper activates

9. Test or replace the KR5 rear defogger relay.

Lower Defogger Grid Inoperative

1. Vehicle OFF, disconnect the KR4B outside rear view mirror heater relay. It may take up to 2 minutes for all vehicle systems to power down.

2. Test for less than 10 ohms between the ground circuit terminal 86 and ground.

• If 10 ohms or greater

1. Vehicle OFF.

2. Test for less than 2 ohms in the ground circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, repair the open/high resistance in the ground connection.

• If less than 10 ohms

3. Verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

• If the test lamp illuminates
Repair the short to voltage on the control circuit

• If the test lamp does not illuminate

4. Vehicle OFF, disconnect the X1 harness connector at the E18B rear defogger grid - lower. It may take up to 2 minutes for all vehicle systems to power down.

5. Test for less than 10 ohms between the ground circuit terminal A and ground.

• If 10 ohms or greater

1. Vehicle OFF.

2. Test for less than 2 ohms in the ground circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, repair the open/high resistance in the ground connection.

• If less than 10 ohms

6. Connect the X2 harness connector at the E18B rear defogger grid - lower.

7. Vehicle in Service Mode, connect a 40 A fused jumper wire between the B+ circuit terminal 43 and the control circuit terminal 42.

8. Verify the E18B rear defogger grid - lower is activated.

• If the E18B rear defogger grid - lower does not activate

1. Vehicle OFF, disconnect the X2 harness connector at the E18B rear defogger grid - lower.

2. Test for infinite resistance between the control circuit and ground.

• If less than infinite resistance, repair the short to ground on the circuit.

• If infinite resistance

3. Test for less than 2 ohms in the control circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, replace the E18B rear defogger grid - lower.

• If the E18B rear defogger grid - lower activates

9. Test or replace the KR4B outside rear view mirror heater relay.

Rear Window Defogger System Inoperative

1. Vehicle OFF, disconnect the KR5 rear defogger relay.

2. Disconnect the KR4B outside rear view mirror heater relay.

3. Connect a test lamp between the control circuit terminal 85 and the ground circuit terminal 86 at the KR4B outside rear view mirror heater relay, Vehicle ON.

4. Verify the test lamp turns ON and OFF commanding the rear window defogger ON and OFF with a scan tool.

• If the test lamp is always OFF

1. Vehicle OFF, disconnect the harness connector at the K33 HVAC control module.

2. Test for infinite resistance between the control circuit and ground.

• If less than infinite resistance, repair the short to ground on the circuit.

• If infinite resistance

3. Test for less than 2 ohms in the control circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, replace the K33 HVAC control module.

• If the test lamp is always ON

1. Vehicle OFF, disconnect the harness connector at the K33 HVAC control module, Vehicle ON.

2. Test for less than 1 V between the control circuit and ground.

• If 1 V or greater, repair the short to voltage on the circuit.

• If less than 1 V, replace the K33 HVAC control module.

• If the test lamp turns ON and OFF

5. Test or replace the KR5 rear defogger relay or the KR4B outside rear view mirror heater relay.

Component Testing

Rear View Mirror Heater Relay Test

1. Vehicle OFF, disconnect the KR4B outside rear view mirror heater relay.

2. Test for 60-180 ohms between terminals 85 and 86.

• If less than 60 ohms or greater than 180 ohms
Replace the KR4B outside rear view mirror heater relay.

• If between 60-180 ohms

3. Test for infinite resistance between the terminals listed below:

* 30 and 86

* 30 and 87

* 30 and 85

* 85 and 87

• If less than infinite resistance
Replace the KR4B outside rear view mirror heater relay.

• If infinite resistance

4. Install a 3 A fused jumper wire between relay terminal 85 and 12 V. Install a jumper wire between relay terminal 86 and ground.

5. Test for less than 2 ohms between terminals 30 and 87.

• If 2 ohms or greater
Replace the KR4B outside rear view mirror heater relay.

• If less than 2 ohms

6. All OK

Rear Defogger Relay Test

1. Vehicle OFF, disconnect the KR5 rear defogger relay.

2. Test for 60-200 ohms between terminals 41 and 40.

• If less than 60 ohms or greater than 200 ohms
Replace the KR5 rear defogger relay.

• If between 60-200 ohms

3. Test for infinite resistance between the terminals listed below:

* 41 and 43

* 41 and 42

* 40 and 43

* 40 and 42

• If less than infinite resistance
Replace the KR5 rear defogger relay.

• If infinite resistance

4. Install a 3 A fused jumper wire between relay terminal 41 and 12 V. Install a jumper wire between relay terminal 40 and ground.

5. Test for less than 2 ohms between terminals 43 and 42.

• If 2 ohms or greater
Replace the KR5 rear defogger relay.

• If less than 2 ohms

6. All OK

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Liftgate Lower Window Replacement Liftgate Lower Window Replacement

* Liftgate Upper Window Replacement Liftgate Upper Window Replacement

* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)

* Control Module References Programming and Relearning for HVAC control module and Radio/HVAC control replacement, programming and setup

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