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Tahoe / Yukon Service Manual

DTC B1066

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. DTC Descriptors DTC B1066 Rear Defogger Relay Control For symptom byte information refer to: Symptom Byte List 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 —
2050 Ground — B1066 13 — —

Circuit/System Description Battery positive voltage is supplied through a 40A fuse in the rear body wiring harness junction block to the rear defogger relay switched input. When the rear window defogger switch is pressed, the body control module commands the rear window defogger system by supplying voltage to the rear defogger relay coil. The rear defogger relay is energized and the defogger indicator is illuminated. With the relay energized, battery positive voltage is allowed from the relay switched input through the switch contacts and out the relay switched output to the rear window defogger grid. Conditions for Running the DTC When the relay is being actively commanded by the body control module Conditions for Setting the DTC B1066 11 Circuit 193= Short to Ground — For greater than 60 s B1066 12 Circuit 193= Short to Battery — For greater than 60 s B1066 13 Circuit 193 or Circuit 2050= Open — For greater than 60 s Action Taken When the DTC Sets The body control module will attempt to command the rear defog relay, but the rear window defogger grid will remain inoperative. C diti f Cl i th DTC Conditions for Clearing the DTC The DTC will be current for as long as the fault is present. When the fault is no longer present, the DTC will be a history DTC. A history DTC will clear after 40 ignition cycles. 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 for scan tool information Circuit/System Verification

  1. Engine Running.
  2. Verify the E18 Rear Window Defogger Grid turns ON and OFF when pressing the appropriate switch on the A26 Heater and Air Conditioning User Interface Control - Front ⇒ If the E18 Rear Window Defogger Grid does not turn ON or OFF Refer to Circuit/System Testing ⇓ If the E18 Rear Window Defogger Grid turns ON and OFF
  3. A fault that is not currently present may have been caused by a intermittent condition. Circuit/System Testing
  4. Ignition OFF and all vehicle systems OFF. It may take up to 2 min for all vehicle systems to power down.
  5. Disconnect the X1 harness connector at the X53A Body Wiring Harness Junction Block - Rear.
  6. 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 3.1. Ignition OFF. 3.2. 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
  7. Connect the X1 harness connector at the X53A Body Wiring Harness Junction Block - Rear. Disconnect the X5 harness connector at the K9 Body Control Module, ignition ON.
  8. Verify the E18 Rear Window Defogger Grid is not activated. ⇒ If the E18 Rear Window Defogger Grid is activated 5.1. Ignition OFF, disconnect the X2 harness connector at the X53A Body Wiring Harness Junction Block - Rear, ignition ON. 5.2. Test for less than 1 V between the K9 Body Control Module circuit 193 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
  9. Connect a 3 A fused jumper wire between the control circuit terminal 22 X5 and B+.
  10. Verify the E18 Rear Window Defogger Grid activates. ⇒ If the E18 Rear Window Defogger Grid does not activate 7.1. Ignition OFF, remove the jumper wire, disconnect the X2 harness connector at the X53A  Body Wiring Harness Junction Block - Rear. 7.2. Test for infinite resistance between the K9 Body Control Module circuit 193 and ground. ⇒ If less than Infinite resistance, repair the short to ground on the circuit. ⇓ If infinite resistance 7.3. 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
  11. Replace the K9 Body Control Module. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Body Wiring Harness Junction Block Replacement Control Module References for the body control module replacement, programming and setup