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Tahoe / Yukon Service Manual

DTC B1B25-B1B28

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 B1B25 Right 3rd Row Folding Seat Back Unlatch Motor Control Low DTC B1B26 Right 3rd Row Folding Seat Back Unlatch Motor Control High DTC B1B27 Left 3rd Row Folding Seat Back Unlatch Motor Control Low DTC B1B28 Left 3rd Row Folding Seat Back Unlatch Motor Control High For symptom byte information refer to Symptom Byte List. Diagnostic Fault Information

Circuit Number Circuit Function Short to Ground Open/Hig Resistanc h Short to e Voltage Signal Performan
8920 Control B1B25 11 B1B25 13 B1B25 12 —
8921 Control B1B26 11 B1B26 13 B1B26 12 —
8922 Control B1B27 11 B1B27 13 B1B27 12 —
8923 Control B1B28 11 B1B28 13 B1B28 12 —

Circuit/System Description The power folding third row seat system consists of folding seat switches, a control module, a seat back release actuator, a hall-effect position sensor, and the folding seat motor. The third row folding seat switches are located on the D-pillar. Voltage to the switches is supplied through the park enable relay while in a de-energized state. The park enable relay is controlled by the body control module (BCM) through a high side drive control circuit and will be de-energized whenever the ignition is in the accessory or run positions and the transmission is in park. Battery voltage is supplied to the folding seat control module through a 30 A fuse located in the rear body fuse block. When a folding seat switch is pressed, battery voltage is applied through the switch contacts and the signal circuit to the folding seat control module indicating the folding seat request. In response to this signal, the module applies a PWM voltage through the seat back release actuator control circuit energizing the actuator. With the actuator energized and the seat back released, the control module applies battery voltage and ground through the folding seat motor control circuits to the motor. The motor runs to either move the seat back cushion to the folded or unfolded seat position. The control module supplies the hall-effect sensor with a low reference and a signal circuit. The module monitors the voltage from the signal circuit in order to detect a seat stall condition. If the module does not detect seat movement within 400ms, it will cease folding seat operation. Conditions for Running the DTC Conditions for Running the DTC Ignition ON Conditions for Setting the DTC B1B25 11, B1B26 11, B1B27 11, or B1B28 11 The K169 Folding 3rd Row Seat Module detects a short to ground for greater than 100 ms. B1B25 12, B1B26 12, B1B27 12, or B1B28 12 The K169 Folding 3rd Row Seat Module detects a short to voltage for greater than 100 ms. B1B25 13, B1B26 13, B1B27 13, or B1B28 13 The K169 Folding 3rd Row Seat Module detects an open/high resistance in a control circuit for greater than 3 s. Action Taken When the DTC Sets The K169 Folding 3rd Row Seat Module will disable all seat functions. Conditions for Clearing the DTC The DTC clears when the diagnostic runs and passes. The history DTC will clear after 40 consecutive fault-free ignition cycles have occurred. Reference Information Schematic Reference Rear Seat Schematics Connector End View Reference Master Electrical Component List Description and Operation Power Seats System 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. Ignition/Vehicle in Service Mode.
  2. Verify that DTC B1B25, B1B26, B1B27, and/or B1B28 are not set. ⇒ If DTC B1B25 and/or B1B26 is set Refer to Circuit/System Testing – B1B25 or B1B26 ⇒ If DTC B1B27 and/or B1B28 is set Refer to Circuit/System Testing – B1B27 or B1B28
  3. Operate all 3rd row power seat functions in the Up/Down or Forward/Rearward directions.
  4. Verify that DTC B1B25, B1B26, B1B27, and/or B1B28 are not set. ⇒ If DTC B1B25 and/or B1B26 is set Refer to Circuit/System Testing – B1B25 or B1B26 ⇒ If DTC B1B27 and/or B1B28 is set Refer to Circuit/System Testing – B1B27 or B1B28 ⇓ If a DTC is not set
  5. A fault is currently not present and may be an intermittent condition. Circuit/System Testing B1B25 or B1B26
  6. Ignition/Vehicle OFF, disconnect the X1 connectors at the K169 Folding 3rd Row Seat Module.
  7. Ignition/Vehicle in Service Mode.
  8. Test for less than 1 V between control circuit terminal 1 and ground. ⇒ If 1 V or greater 3.1. Test circuit 8921 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 3.2. Test circuit 8920 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 3.3. Replace the M109RR Folding 3rd Row Seat Back Actuator - Right. ⇓ If less than 1 V
  9. Ignition/Vehicle OFF.
  10. Test for infinite resistance between control circuit terminal 1 and ground. ⇒ If less than infinite resistance 5.1. Test circuit 8921 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 5.2. Test circuit 8920 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 5.3. Replace the M109RR Folding 3rd Row Seat Back Actuator - Right. ⇓ If infinite resistance
  11. Test for less than infinite resistance between control circuit terminal 1 and control circuit terminal 2. ⇒ If infinite resistance 6.1. Test circuit 8921 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 6.2. Test circuit 8920 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 6.3. Replace the M109RR Folding 3rd Row Seat Back Actuator - Right. ⇓ If less than infinite resistance
  12. Replace the M109RR Folding 3rd Row Seat Back Actuator - Right.
  13. Connect the X1 connector at the K169 Folding 3rd Row Seat Module.
  14. Clear all DTCs.
  15. Operate all 3rd row power seat functions in the Up/Down or Forward/Rearward directions.
  16. Verify DTC B1B25 and/or B1B26 do not set. ⇒ If any DTC sets Replace the K169 Folding 3rd Row Seat Module. ⇓ If no DTC sets
  17. All OK. B1B27 or B1B28
  18. Ignition/Vehicle OFF, disconnect the X2 connectors at the K169 Folding 3rd Row Seat Module.
  19. Ignition/Vehicle in Service Mode.
  20. Test for less than 1 V between control circuit terminal 12 and ground. ⇒ If 1 V or greater 3.1. Test circuit 8923 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 3.2. Test circuit 8922 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 3.3. Replace the M109LR Folding 3rd Row Seat Back Actuator - Left. ⇓ If less than 1 V
  21. Ignition/Vehicle OFF.
  22. Test for infinite resistance between control circuit terminal 12 and ground. ⇒ If less than infinite resistance 5.1. Test circuit 8923 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 5.2. Test circuit 8922 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 5.3. Replace the M109LR Folding 3rd Row Seat Back Actuator - Left. ⇓ If infinite resistance
  23. Test for less than infinite resistance between control circuit terminal 11 and control circuit terminal 12. ⇒ If infinite resistance 6.1. Test circuit 8923 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 6.2. Test circuit 8922 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 6.3. Replace the M109LR Folding 3rd Row Seat Back Actuator - Left. ⇓ If less than infinite resistance
  24. Replace the M109LR Folding 3rd Row Seat Back Actuator - Left.
  25. Connect the X2 connector at the K169 Folding 3rd Row Seat Module.
  26. Clear all DTCs.
  27. Operate all 3rd row power seat functions in the Up/Down or Forward/Rearward directions.
  28. Verify DTC B1B27 and/or B1B28 do not set. ⇒ If any DTC sets Replace the K169 Folding 3rd Row Seat Module. ⇓ If no DTC sets
  29. All OK. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Control Module References for K169 Folding 3rd Row Seat Module replacement, programming and setup.