B2A5913 - B2A5913 Driver Foot Vent Outlet Temperature Sensor Open Circuit

B2A5913 Driver Side Foot Air Outlet Temperature Sensor Open Circuit Diagnostic Technical Description

Fault Depth Definition

DTC code B2A5913 is defined as "Driver Side Foot Air Outlet Temperature Sensor Open Circuit" in the vehicle global network. In the HVAC thermal management system architecture, this sensor plays a key feedback actuator role, responsible for real-time collection of air temperature data from the driver side foot outlet area. The control unit regulates blower speed and mixing flap opening by monitoring the signal voltage to achieve the preset cabin temperature feedback loop. The term "Open Circuit" refers to an abnormal increase in electrical impedance detected by the control unit at the signal line, causing the input pin voltage to be unable to stabilize within the expected voltage divider range, thereby determining a break or high-impedance fault in the sensor circuit, interrupting the real-time feedback information flow of physical position and rotation speed (i.e., temperature value).

Common Fault Symptoms

When this fault code is illuminated, vehicle drivers and passengers may observe the following system response behaviors:

• HVAC System Partial Function Failure: Automatic temperature control mode may fail to accurately execute target temperature settings; the system may enter a protection mode or temporarily disable automatic regulation functions, forcing a switch to manual control.
• Instrument Panel Fault Indicator Lights On: The instrument panel may show an HVAC system warning light indicating sensor communication interruption or signal abnormalities.
• Foot Outlet Air Temperature Display Abnormality: The current actual temperature value displayed on the vehicle screen for the foot outlet is lost, displays a default value, or cannot update in real-time with ambient temperature changes.
• Cooling/Heating Efficiency Fluctuation: Due to lack of accurate feed-forward/feed-back signals, the HVAC system may misjudge environmental load, leading to unstable foot blower air volume or cold air output, affecting driving and riding comfort.

Core Fault Cause Analysis

According to fault diagnosis logic and electrical architecture analysis, the circuit abnormality is mainly caused by the following three physical dimensions:

• Hardware Component (Driver Side Foot Air Outlet Temperature Sensor): The thermistor element inside the sensor has permanently damaged, leading to loss of sensing capability; or the signal line physically disconnects at the internal sensor pins, resulting in inability to output correct voltage pulses or analog values.
• Wiring/Connector (Harness or Connector Failure): The power and signal loop from the sensor to the control unit exist physical breakage, poor soldering or plug terminals oxidation loosening, causing high impedance connection; also need to pay attention to whether there is abnormal conduction between signal line and power positive pole, leading to voltage being pulled high.
• Controller (Left Domain Controller Fault): The left area integrated domain controller is responsible for ADC conversion and logic determination of the sensor signal. If the A/D converter inside the controller is damaged or the reference voltage circuit is unstable, it may also falsely report open circuit signal, unable to correctly identify normal low-level signals.

Technical Monitoring and Trigger Logic

Ecu's diagnosis of the Driver Side Foot Air Outlet Temperature Sensor is based on dynamic voltage threshold judgment, specific monitoring logic as follows:

• Monitoring Target: Control unit input end sensor analog output voltage signal.
• Value Judgment Range: The system has strict voltage thresholds set. When signal voltage detected is higher than $4.95V$, it is determined as open circuit fault (Open Circuit). This voltage value usually lies in the characteristic interval of signal line disconnection or mistakenly connected high potential, indicating the sensor cannot pull the signal to the normal working low level area.
• Specific Operating Condition Requirements: Faults are only recorded as fault codes when the ignition switch is placed in ON position and system self-check passes. At this time the control unit is in monitoring active state, if the sensor does not correctly pull down voltage to a reasonable range, then immediately meet trigger conditions and store fault code B2A5913.