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Tahoe / Yukon Service Manual

DTC B1236 or B1AE7

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 B1236 Backup Lamp Supply Voltage Circuit DTC B1AE7 Backup Lamp Supply Voltage 2 Circuit Refer to Symptom Byte List for symptom byte information. Diagnostic Fault Information

Circuit Circuit Function Short to Ground Open/Hig Resistance h Short to Voltage Signal Performan
24 Control B1236 11 1 1 —
1324 Control B1AE7 11 1 1 —
1950 Ground — 1 — —
2050 Ground — 1 — —
1. Backup Lamps Malfunction

Scan Tool Functions K219 Lighting Control Module – Control Functions – Exterior Lighting

Control Function Description
Left Backup Lamp Command This control function will control the left backup lamp ON/OFF
Right Backup Lamp Command This control function will control the right backup lamp ON/OFF

Circuit/System Description With the engine running and the transmission in the reverse position, the transmission control module (TCM) sends a serial data message to the K9 Body Control Module (BCM). The message indicates that the gear selector is in the reverse position. The BCM responds by sending a serial data message to the K219 Lighting Control Module. The Lighting Control Module responds by applying battery voltage to the backup lamp control circuits illuminating the backup lamps. Once the driver moves the gear selector out of the reverse position, a serial data message is sent by the TCM that the transmission is no longer in the reverse position. The engine must be running for the backup lamps to operate. Conditions for Running the DTC Battery voltage must be between 9-16 V. Engine running. Transmission placed in reverse gear. Conditions for Setting the DTC DTC B1236 11 The Lighting Control Module detects a short to ground on control circuit 24. DTC B1236 13 The Lighting Control Module detects an open/high resistance on control circuit 24. DTC B1AE7 11 The Lighting Control Module detects a short to ground on control circuit 1324. DTC B1AE7 13 The Lighting Control Module detects an open/high resistance on control circuit 1324. Actions Taken When the DTC Sets The backup lamp will not operate. Conditions for Clearing the DTC The condition responsible for setting the DTC no longer exists. A history DTC will clear once 40 consecutive malfunction-free ignition cycles have occurred. Reference Information Schematic Reference Exterior Lights Schematics Connector End View Reference Master Electrical Component List Description and Operation Exterior Lighting Systems 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 Testing DTC B1236

  1. Ignition/vehicle OFF, exterior lamps OFF, disconnect the E42L Rear Body Structure Stop Lamp - Left.
  2. Verify a test lamp illuminates between ground circuit terminal 1 and B+. ⇒ If the test lamp does not illuminate 2.1. Repair the open/high resistance on the ground circuit or ground connection. ⇓ If the test lamp illuminates
  3. Connect a test lamp between control circuit terminal 4 and ground, ignition ON/vehicle in service mode.
  4. Verify the test lamp turns ON and OFF when commanding the Left Backup Lamp Command ON and OFF with a scan tool. ⇒ If the test lamp is always OFF 4.1. Test circuit 24 for a short to ground. ⇒ If a short to ground is found, repair the fault on the circuit. ⇓ If a short to ground is not found 4.2. Test circuit 24 for an open/high resistance. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found 4.3. Replace the K219 Lighting Control Module. ⇒ If the test lamp is always ON 4.1. Test circuit 24 for a short to voltage. ⇒ If a short to voltage is found, repair the fault on the circuit. ⇓ If a short to voltage is not found 4.2. Replace the K219 Lighting Control Module. ⇓ If the test lamp turns ON and OFF
  5. Replace the backup lamp. DTC B1AE7
  6. Ignition/vehicle OFF, exterior lamps OFF, disconnect the E42R Rear Body Structure Stop Lamp
  • Right.
  1. Verify a test lamp illuminates between ground circuit terminal 1 and B+. ⇒ If the test lamp does not illuminate 2.1. Repair the open/high resistance on the ground circuit or ground connection. ⇓ If the test lamp illuminates
  2. Connect a test lamp between control circuit terminal 4 and ground, ignition ON/vehicle in service mode.
  3. Verify the test lamp turns ON and OFF when commanding the Right Backup Lamp Command ON and OFF with a scan tool. ⇒ If the test lamp is always OFF 4.1. Test circuit 1324 for a short to ground. ⇒ If a short to ground is found, repair the fault on the circuit. ⇓ If a short to ground is not found 4.2. Test circuit 1324 for an open/high resistance. ⇒ If an open/high resistance is found, repair the fault on the circuit. ⇓ If an open/high resistance is not found 4.3. Replace the K219 Lighting Control Module. ⇒ If the test lamp is always ON 4.1. Test circuit 1324 for a short to voltage. ⇒ If a short to voltage is found, repair the fault on the circuit. ⇓ If a short to voltage is not found 4.2. Replace the K219 Lighting Control Module. ⇓ If the test lamp turns ON and OFF
  4. Replace the backup lamp. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Lighting Component Replacement Reference Control Module References for BCM replacement, programming, and setup