B2A4B92 - B2A4B92 Recirculation Motor Not Reaching Position

Fault Definition

DTC B2A4B92 refers to a system-level fault code indicating that the circulation motor cannot accurately reach its target position. In the vehicle thermal management system, the circulation motor acts as an actuator; its core function is to drive flap or guide vane physical displacement between different modes of the air conditioning system (such as switch between internal and external circulation), thereby adjusting the air circulation path and control logic inside the cabin in real time. When the Control Unit (CCU) acquires signals on the AD40 analog-to-digital conversion channel, if an abnormally low feedback voltage is detected (detection voltage below $0.2V$), it determines that the motor has failed to complete action or there is a signal circuit anomaly. The establishment of this fault code aims to protect the logical integrity of the vehicle thermal management system, preventing air conditioning malfunction caused by actuator position deviation.

Common Fault Symptoms

When DTC B2A4B92 is activated, the vehicle's thermal management system will enter a protection mode, and the car owner may observe the following driving experience changes and instrument panel feedback:

• The airflow direction or circulation mode at the air outlet inside the vehicle cannot switch to "Recirculation", and the system locks in the default state.
• The air conditioning control indicator light on the instrument cluster flashes or displays warning information such as "Air Circulation System Abnormal".
• The vehicle's automatic air conditioning system may refuse to execute air volume distribution commands set by the driver due to inability to verify closed-loop signals.
• Overall thermal efficiency drops, interior air quality regulation capability is partially ineffective, and external pollutants cannot be effectively isolated.

Core Fault Cause Analysis

Based on the diagnostic logic of the right-side domain controller, this fault can be broken down into three dimensions of potential hardware or software factors:

• Hardware Components (Circulation Motor): Internal coil open circuit in the circulation motor, rotor sticking causing inability to reach target physical position, or abnormal Hall sensor signal output, unable to provide accurate position feedback voltage to CCU.
• Line/Connector Faults: Wiring harness connecting the right-side domain controller to the actuator motor has open circuit, short circuit, or loose connection; signal line impedance from CCU side AD40 sampling pin to motor end is too high causing abnormal voltage division; connector pin oxidation or looseness causes excessive contact resistance.
• Controller (Right Domain Controller/CCU): Control unit internal ADC sampling circuit fault, unable to correctly identify voltage threshold; program logic judgment error or DTC storage condition not met; power management module power supply fluctuation leading to unstable AD40 reference voltage.

Technical Monitoring & Trigger Logic

The judgment of this fault code is based on strict timing signals and electrical parameter monitoring mechanisms, specific logic as follows:

• Monitoring Target: The system continuously monitors the feedback signal voltage value collected by the analog-to-digital converter (ADC) inside the CCU on a specific channel AD40.
• Trigger Threshold Condition: The CCU sets detection voltage must be below $0.2V$ (AD40), which is regarded as an invalid signal or open circuit state.
• Operating Condition Dependency: Fault judgment is performed only when the vehicle is in running state and the ignition switch is set to IGN ON/OK condition, ensuring DTC setting enablement conditions are met.
• Logic Flow: After system initialization completes and enters self-check mode, if the motor's AD40 end voltage continuously stays below $0.2V$ during driving action and meets minimum time constant for continuous duration, the control unit will officially record fault code B2A4B92 and light up relevant instrument panel warnings.