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Tahoe / Yukon Service Manual

DTC B124E or B1251

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 B124E Right Rear Seat Heating High Indicator Control DTC B1251 Left Rear Seat Heating High Indicator Control Symptom Byte Information: Symptom Byte List Circuit/System Description The right rear and left rear heated seats switches are located within the A34 Heater and Air Conditioning Auxiliary Control. To operate the heated seats the engine must be running. When a heated seat switch is pressed, a serial data message is sent from the A34 Heater and Air Conditioning Auxiliary Control to the K9 Body Control Module (BCM) indicating the heated seat command. The BCM serves as the heated seat system master to determine the requested operating mode. The BCM then sends a LIN bus serial data message to the K29RV Rear Seat Heater Vent Control Module indicating the heated seat command. In response to this message, the K29RV Rear Seat Heater Vent Control Module attempts to drive the appropriate seat heating elements per the BCM command. The BCM also controls the seat temperature and mode indicators, via the serial data line, used to provide the operator with feedback as to the operating status of the system. The K29RV Rear Seat Heater Vent Control Module controls heated seat operation for the driver and passenger seats. When active, power is applied to the seat cushion and back heater elements through a common pulse width modulated (PWM) voltage supply control circuit. Each individual heater element is switched to ground by the module through a common low side drive control circuit. The seat back and cushion temperature sensors (thermistors) are packaged with the seat heating elements located just under the seat covers. The K29RV Rear Seat Heater Vent Control Module supplies each temperature sensor with a 5 V reference signal circuit and a low reference circuit. The module monitors the voltage from the signal circuit to determine the temperature of the seat. The temperature sensor varies in resistance based on the temperature of the heating element causing the signal voltage to change. Once the module senses the seat reached the set temperature, it will then begin regulate the current flow through the heater elements in order to maintain the desired seat temperature based on the feedback voltage from the sensor. Conditions for Running the DTC Ignition ON Conditions for Setting the DTC B124E The control module detects an internal fault with the right rear seat heating indicator. B1251 The control module detects an internal fault with the left rear seat heating indicator. Action Taken When the DTC Sets The seat heater control module may disable all heated 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 Heated/Cooled Seat Schematics Connector End View Reference Master Electrical Component List Description and Operation Rear Heated Seats 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 ON.
  2. Verify DTC B124E or B1251 is not set. ⇒ If the DTC is set Replace the A34 Heater and Air Conditioning Auxiliary Control. ⇓ If the DTC is not set
  3. A fault is currently not present and may be an intermittent condition. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair.