B2A5A13 - B2A5A13 Passenger Face Vent Outlet Temp Sensor Open Circuit

Fault Definition

The fault code B2A5A13 specifically diagnoses the passenger side face outlet air temperature sensor circuit in the vehicle's HVAC system; this fault type is defined as "Open Circuit" (Open Circuit). In the electronic electrical architecture, this sensor serves as a key link in the HVAC closed-loop control, providing real-time environmental data to the Body Control Unit (CCU). The term "Open Circuit" indicates that the CCU cannot detect the expected low-level signal voltage from the sensor, typically manifested as a circuit break or high impedance state, causing feedback loop failure. This fault triggers a safety protection mechanism, putting the HVAC system into partial functional failure mode to prevent the controller from adjusting actuators based on erroneous data.

Common Fault Symptoms

When this DTC is activated, the vehicle's actual performance is closely related to the driver and occupants' perceived experience, with symptoms expanded as follows:

• Partial HVAC Function Failure: The passenger side face outlet temperature automatic control capability is lost, and the system may force default to off state or fixed mode.
• Dashboard Feedback Abnormal: Related fault lamp prompts may appear on the central screen or instrument panel, or sensor data may display as overflow/invalid values.
• Comfort Degradation: Passengers cannot adjust passenger side outlet temperature via automatic climate logic, requiring manual intervention or physical temperature control valves.
• System Enters Safe Mode: The Electronic Control Unit (ECU) stops attempting to drive related execution motors or valves based on fault signals to protect hardware from damage.

Core Fault Cause Analysis

Based on DTC raw data and system architecture logic, the root cause can be summarized into three technical dimensions:

1. Hardware Component Anomaly

   • The passenger side face outlet temperature sensor itself suffers internal open circuit damage, preventing the formation of an effective voltage divider loop, leaving the signal output terminal floating.

2. Wiring and Connector Faults

   • Physical open circuits, abrasion, or insulation damage exist in the harness connecting CCU and the sensor.
   • Connector terminals experience loose connection, oxidation corrosion, or pin retraction phenomena, causing excessive contact impedance and signal transmission interruption.

3. Controller Logic Anomaly

   • The Right Domain Controller or its internally integrated temperature processing module malfunctions, causing voltage acquisition circuit baseline drift or misjudgment of sensor signals, erroneously determining an open circuit state.

Technical Monitoring & Trigger Logic

System fault judgment is based on strict electrical parameter monitoring and specific operating conditions, with logic as follows:

• Monitoring Target: CCU (Climate Control Unit) continuously monitors the analog output signal voltage value of the temperature sensor.
• Judgment Threshold: When CCU detects the sensor output voltage higher than $4.95V$, the system determines the circuit is in an open state (Open Circuit typically results in voltage close to supply rail voltage).
• DTC Setup Enable Condition: The fault is recorded only when the ignition switch is in IGN ON/OK status and the system completes initialization self-check.
• Specific Operating Conditions Requirement: This fault determination trigger relies on signal validity monitoring during static or low-speed cruising; once signal deviates continuously from expected range beyond preset time threshold, it will finally generate B2A5A13 fault code and store it in fault memory.