Document ID: 1736375

Note: If it has been observed during use that a grid line is inoperative, the following procedure can be used to find the break. If none of the grid lines is operating, a full system diagnosis should be completed before attempting to test the grid lines

Note: Lightly touch the grid lines when testing with the test lamp. If the test lamp point is scraped through the grid line it can cause an open in the circuit

Engine running, command the Rear Defogger ON with a scan tool.
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.
The grid line is open between the test point and the ground side of the grid.
Replace the rear window

If the test lamp remains off at the middle of the grid line.
The grid line is open between the test point and the voltage supply side of the grid.
Replace the rear window

If the test lamp remains dim at the middle of each grid line.

All OK

Document ID: 4962222

Diagnostic Instructions

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
Review Strategy Based Diagnosis for an overview of the diagnostic approach.
Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Rear Defogger Relay B+	1	1	—	—
Rear Defogger Relay Control	B0283 02	B0283 05	B0283 05	—
Rear Defogger Grid Control	1	1	2	—
Rear Defogger Relay Ground	—	B0283 05	—	—
Rear Defogger Grid Ground	—	1	—	—
1. Rear Defogger Inoperative 2. Rear Defogger Always ON

Circuit/System Description

When the HVAC control module receives a rear window defog request from the radio/HVAC control, 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 current from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger grid.

Diagnostic Aids

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

The battery state of charge is out of range causing the HVAC control module to suspend the rear window defogger operation.
The Remote Start Enable ambient temperature is greater than 5°C (40°F).

Reference Information

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

Circuit/System Verification

Engine running.
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

Verify the E18 Rear Defogger Grid turns ON and OFF when commanding the Rear Defogger On and Off with a scan tool.

If the E18 Rear Defogger Grid does not turn ON and OFF
Refer to Circuit/System Testing

If the E18 Rear Defogger Grid turns ON and OFF

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

All OK.

Circuit/System Testing

Ignition OFF and all vehicle systems OFF, disconnect the KR5 Rear Defogger Relay. It may take up to 2 minutes for all vehicle systems to power down.
Test for less than 10 Ω between the ground circuit terminal 86 and ground.

If 10 Ω or greater

Ignition OFF.
Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.
If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

Engine Running.
Verify a test lamp illuminates between the B+ circuit terminal 30 and ground.

If the test lamp does not illuminate
Replace the X50A Fuse Block-Underhood

If the test lamp illuminates

Connect a test lamp between the control circuit terminal 85 and the ground circuit terminal 86.
Verify the test lamp turns ON and OFF when commanding the Rear Defogger On and Off with a scan tool.

If the test lamp is always OFF

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

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

If 2 Ω or greater, repair the open/high resistance in the circuit.
If less than 2 Ω, replace the K33 HVAC control module.

If the test lamp is always ON

Ignition OFF, disconnect the harness connector at the K33 HVAC control module, ignition ON.
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

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

Ignition OFF and all vehicle systems OFF, disconnect the X2 harness connector at the E18 Rear Defogger Grid. It may take up to 2 minutes for all vehicle systems to power down.
Test for less than 10 Ω between the ground circuit terminal 1 and ground.

If 10 Ω or greater

Ignition OFF.
Test for less than 2 Ω in the ground circuit end to end.

If 2 Ω or greater, repair the open/high resistance in the circuit.
If less than 2 Ω, repair the open/high resistance in the ground connection.

If less than 10 Ω

Connect the X2 harness connector at the E18 Rear Defogger Grid.
Ignition ON, connect a 30 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87.
Verify the E18 Rear Defogger Grid is activated.

If the E18 Rear Defogger Grid does not activate

Ignition OFF, disconnect the X1 harness connector at the E18 Rear Defogger Grid.
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

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

If 2 Ω or greater, repair the open/high resistance in the circuit.
If less than 2 Ω, test or replace the E18 Rear Defogger Grid.

If the E18 Rear Defogger Grid activates

Test or replace the KR5 Rear Defogger Relay.

Component Testing

Relay Test

Ignition OFF, disconnect the KR5 Rear Defogger Relay.
Test for 60-180 Ω between terminals 85 and 86.

If less than 60 Ω or greater than 180 Ω
Replace the KR5 Rear Defogger Relay.

If between 60-180 Ω

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 KR5 Rear Defogger Relay.

If infinite resistance

Install a 3 A fused jumper wire between relay terminal 85 and 12 V. Install a jumper wire between relay terminal 86 and ground.
Test for less than 2 Ω between terminals 30 and 87.

If 2 Ω or greater
Replace the KR5 Rear Defogger Relay.

If less than 2 Ω

All OK

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Rear Window Replacement
Electrical Relay Replacement
Control Module References for HVAC control module and radio/HVAC controls replacement, programming and setup

Heated Glass Element