B2A5813 - B2A5813 Driver Face Vent Outlet Temp Sensor Open Circuit

Fault Depth Definition

DTC B2A5813 is defined as "Driver side blow face temperature sensor open circuit". In automotive comfort control system architecture, this code identifies a monitoring anomaly of the Central Control Unit (CCU) regarding specific analog signal input status. Specifically, "open circuit" in circuit theory represents a high-impedance state, indicating internal sensor loop disconnection or external wiring breakage, causing CCU to be unable to collect valid thermistor divider values. When control unit detects feedback loop voltage signals exceeding expected low-level range, system determines open circuit fault. This definition clarifies that this fault code reflects the electrical connection integrity issue of the temperature sensing function in the driver side blow face area, not merely measurement deviation, directly impacting HVAC closed-loop temperature control logic calculation.

Common Fault Symptoms

After DTC B2A5813 is recorded, vehicle HVAC system enters protective degraded mode, perceivable specific symptoms include:

• HVAC Partial Function Failure: Driver side blow face area no longer participates in automatic temperature control loop, may appear large difference between set temp and actual outlet temp.
• Comfort Zone Control Restricted: Personalized blow face temperature adjustment functions involving driver side may be disabled or fixed to default mode.
• Fault Indicator Light Status: Dashboard HVAC warning light may turn on, and onboard diagnostic system enters permanent fault storage mode (Pending DTC).
• System Logic Lock: Control unit will no longer update temperature feedback data for that area until fault is resolved and reset procedure completed.

Core Fault Cause Analysis

Based on electrical principles and architecture topology, occurrence of this fault can be attributed to physical or logical factors in following three dimensions:

• Hardware Component Failure: Driver side blow face temperature sensor failure, e.g., internal NTC thermistor element internal breakage, solder point delamination or sensing medium failure, causing inability to form closed loop.
• Wiring and Connector Connection Abnormality: Harness or connector fault, including sensor signal line crushed/cut, connector pin pull-back corrosion, loose connector or not fully locked, causing physical path interruption.
• Controller Logic or Hardware Failure: Right domain controller failure, referring to Central Control Unit responsible for reading the signal internal A/D conversion circuit damaged or input end protection diode breakdown, leading to voltage sampling reference failure.

Technical Monitoring and Trigger Logic

System fault judgment follows strict timing and voltage threshold logic, specific technical parameter settings as follows:

• Monitoring Target Signal: CCU continuously monitors driver side blow face temperature sensor output analog voltage value.
• Fault Judgment Threshold: CCU detects sensor output voltage higher than $4.95V$. In normal closed loop, signal should be in lower voltage range (e.g., close to $0V$); once open circuit causes current cutoff, pull-up resistor will pull voltage up near reference voltage, exceeding $4.95V$ is considered abnormal.
• Operating Condition Requirement: DTC Setting Enable, control unit executes this check only when system initialization complete and related function activated.
• Power Condition: IGN ON/OK, must be monitored during ignition switch opened and whole vehicle power network stable period, ensuring voltage sampling data validity.

Once all above fault conditions are met, CCU will lock the fault code and stop outputting temperature regulation requests for driver side blow face area.