B2A5913 - B2A5913 Driver Foot Vent Outlet Temp Sensor Open Circuit

Fault Depth Definition

B2A5913 Driver side footwell outlet temperature sensor open circuit is a critical diagnostic trouble code in the vehicle heating, ventilation, and air conditioning (HVAC) control network. This fault code is triggered primarily during interaction between the Central Controller Unit (CCU, i.e., Right Domain Controller) and the Left Front Area, used to monitor the feedback loop at the position of the driver's footwell outlet vent. In the vehicle thermal management system, this sensor plays a crucial role in providing feedback on physical location and rotational speed functions—here specifically manifested as accurately sensing the real-time temperature value of the footwell outlet and transmitting it back to the controller for logical computation. When the system detects that the sensor signal voltage is at an abnormally high level, CCU determines that it cannot obtain valid closed-loop control data for temperature, thus marking this circuit state as open (Open Circuit) to ensure the system does not execute heating or cooling instructions based on erroneous feedback.

Common Fault Symptoms

When fault code B2A5913 is activated, vehicle drivers may perceive the following specific experience changes on the dashboard and HVAC functions:

• Partial HVAC System Function Failure: The automatic temperature control function of the HVAC system may be temporarily disabled, causing the footwell outlet vent temperature to be unable to output stably according to the set value.
• Dashboard Fault Indicator Light On: Related HVAC warning icons may appear in the vehicle information system, prompting the driver to pay attention to communication or sensor abnormalities in the air conditioning control module.
• Heat/Cold Air Mode Fluctuation: Although the system is not fully turned off, unexpected jumps between hot and cold airflow temperatures or inability to maintain the set temperature may occur under specific operating conditions.
• Default Mode Operation: Some models will force a switch to failure protection mode (Failsafe Mode), such as defaulting to blowing hot air or stopping execution of temperature adjustment commands.

Core Fault Cause Analysis

Based on the original data characteristics of this DTC, the root causes of the fault can be summarized into technical anomalies in the following three dimensions:

• Hardware Component Failure: Electronic components inside the left front footwell outlet temperature sensor fail, causing it to be unable to convert the physical quantity of temperature into a standard voltage signal. According to open circuit detection logic, internal component damage may cause infinite increase in internal impedance or physical disconnection of connection points.
• Wiring and Connector Faults: The harness connecting CCU and sensor is broken, shorted, or has poor contact; or the relevant vehicle electrical connectors (connectors) wear out due to vibration, causing pin withdrawal, corrosion or oxidation, resulting in signal transmission interruption manifested as high level.
• Controller Logic Computation Failure: The voltage monitoring module or digital processing unit inside the Right Domain Controller (Right Domain Controller / CCU) makes an erroneous judgment; incorrectly marking an open circuit state when the received analog signal has not exceeded the threshold, belonging to abnormal control logic at the logical level.

Technical Monitoring & Trigger Logic

The B2A5913 determination mechanism follows strict real-time data monitoring and logic thresholds, with specific technical details as follows:

• Monitoring Target: CCU continuously monitors the analog signal voltage value in the left front footwell outlet temperature sensor loop, used to verify whether the signal is within a normal voltage divider resistor range.
• Numerical Threshold Range: The fault trigger condition is when the sensor output voltage detected by CCU is higher than the preset threshold. The specific judgment criteria show the voltage must meet the following conditions: $>4.95V$. When the signal enters high level state beyond this interval, the system considers it an open circuit fault.
• Specific Conditions & Activation Timing: Fault logic starts to work only when the ignition switch is in the "IGN ON/OK" enabled state. Only when vehicle power is active and DTC setting enable (Enable) is completed will CCU perform real-time comparison against voltage threshold and finally lock the fault code.