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Tahoe / Yukon Service Manual

Rear Window Defogger Malfunction

Diagnostic Instructions Perform the Diagnostic System Check prior to using this diagnostic procedure: Diagnostic System Check - Vehicle Review the description of Strategy Based Diagnosis: Strategy Based Diagnosis An overview of each diagnostic category can be found here: Diagnostic Procedure Instructions Diagnostic Fault Information

Circuit number Circuit Function Short to Ground Open/High Resistance Short to Voltage Signal Performan
193 Control B1066 11 B1066 13 B1066 12 —
293 Control 1 1 2 —
2050 Ground — B1066 13 — —
1. Rear window defogger grid Inoperative 2. Rear window defogger grid always ON

Circuit/System Description When the rear window defogger switch is pressed, the K9 Body Control Module will provide B+ to the control circuit 193 which energizes the PCB KR5 Rear Window Defogger Relay. 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 control circuit  293. Reference Information Schematic Reference Defogger Schematics Connector End View Reference Master Electrical Component List Description and Operation Rear Window Defogger Description and Operation Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs Scan Tool Reference Control Module References Circuit/System Verification

  1. Ignition » On / Vehicle » In Service Mode
  2. Operate the component: Rear Defogger Switch » Pressed Verify the component turns On and Off: E18 Rear Window Defogger Grid ⇒ If the component does not turn On and Off Refer to: Circuit/System Testing ⇓ If the component turns On and Off
  3. A fault is not currently present and may be an intermittent condition Circuit/System Testing
  4. Ignition OFF and all vehicle systems OFF, disconnect the X1 and X2 harness connectors at the E18 Rear Window Defogger Grid. It may take up to 2 min for all vehicle systems to power down.
  5. Test for less than 10 Ω between the E18 Rear Window Defogger Grid ground circuit terminal 1 X2 and ground. ⇒ If 10 Ω or greater 2.1. Ignition OFF. 2.2. 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
  6. Connect a test lamp between the control circuit terminal 1 X1 and ground, ignition ON.
  7. Verify the test lamp does not turn ON and OFF when pressing the appropriate switch on the A26 Heater and Air Conditioning User Interface Control - Front ⇒ If the test lamp turns ON and OFF Test or replace the E18 Rear Window Defogger Grid. ⇓ If the test lamp does not turn ON and OFF
  8. Ignition OFF, connect the X1 and X2 harness connectors at the E18 Rear Window Defogger Grid. Disconnect the X1 and X2 harness connectors at the X53A Body Wiring Harness Junction Block - Rear, ignition ON.
  9. Verify the E18 Rear Window Defogger Grid is not activated. ⇒ If the E18 Rear Window Defogger Grid is activated 6.1. Ignition OFF, disconnect the X1 harness connector at the E18 Rear Window Defogger Grid, ignition ON. 6.2. Test for less than 1 V between the E18 Rear Window Defogger Grid control circuit terminal  1 and ground. ⇒ If 1 V or greater, repair the short to voltage on the circuit. ⇒ If less than 1 V, test or replace the E18 Rear Window Defogger Grid. ⇓ If the E18 Rear Window Defogger Grid is not activated
  10. Connect a 40 A fused jumper wire between the control circuit terminal 17 X2 and B+.
  11. Verify the E18 Rear Window Defogger Grid activates. ⇒ If the E18 Rear Window Defogger Grid does not activate 8.1. Ignition OFF, remove the jumper wire, disconnect the X1 harness connector at the E18  Rear Window Defogger Grid. 8.2. Test for infinite resistance between the E18 Rear Window Defogger Grid control circuit terminal 1 and ground. ⇒ If less than Infinite resistance, repair the short to ground on the circuit. ⇓ If infinite resistance 8.3. 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, all OK. ⇓ If the E18 Rear Window Defogger Grid activates
  12. Ignition OFF and all vehicle systems OFF. It may take up to 2 min for all vehicle systems to power down.
  13. Test for less than 10 Ω between the X53A Body Wiring Harness Junction Block - Rear ground circuit terminal 5 X1 and ground. ⇒ If 10 Ω or greater 10.1. Ignition OFF. 10.2. 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
  14. Connect the X1 and X2 harness connectors at the X53A Body Wiring Harness Junction Block - Rear. Disconnect the X5 harness connector at the K9 Body Control Module, ignition ON.
  15. Verify the E18 Rear Window Defogger Grid is not activated. ⇒ If the E18 Rear Window Defogger Grid is activated 12.1. Ignition OFF, disconnect the X2 harness connector at the X53A Body Wiring Harness Junction Block - Rear, ignition ON. 12.2. Test for less than 1 V between the K9 Body Control Module control circuit terminal 22 X5 and ground. ⇒ If 1 V or greater, repair the short to voltage on the circuit. ⇒ If less than 1 V, test or replace the X53A Body Wiring Harness Junction Block - Rear. ⇓ If the E18 Rear Window Defogger Grid is not activated
  16. Connect a 3 A fused jumper wire between the control circuit terminal 22 X5 and B+.
  17. Verify the E18 Rear Window Defogger Grid activates. ⇒ If the E18 Rear Window Defogger Grid does not activate 14.1. Ignition OFF, remove the jumper wire, disconnect the X2 harness connector at the X53A  Body Wiring Harness Junction Block - Rear. 14.2. Test for infinite resistance between the K9 Body Control Module control circuit terminal  22 X5 and ground. ⇒ If less than Infinite resistance, repair the short to ground on the circuit. ⇓ If infinite resistance 14.3. 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 X53A Body Wiring Harness Junction Block - Rear. ⇓ If the E18 Rear Window Defogger Grid activates
  18. Replace the K9 Body Control Module. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification Body Wiring Harness Junction Block Replacement Rear Compartment Lift Window Replacement For control module replacement, programming, and setup refer to: Control Module References