B2A2413 - B2A2413 Evaporator Temperature Sensor Open Circuit

Fault Depth Definition

DTC Code B2A2413 Evaporator Temperature Sensor Open Circuit is a core diagnostic identifier used by the HVAC Control Unit for monitoring thermal management system status. This fault code indicates that the system has detected an abnormally high impedance state in the feedback loop of the evaporator temperature sensor, meaning circuit disconnection or unexpected breakage in the signal line. Within the electronic electrical architecture, the control unit continuously monitors sensor voltage to infer physical temperature; when open circuit occurs, circuit integrity is compromised, causing the sensor to be unable to provide effective thermodynamic parameter feedback to the domain controller. This definition emphasizes the control unit's real-time validation logic for sensor output signals, ensuring that the air conditioning compressor and blower actuators can operate under accurate thermal load conditions.

Common Fault Symptoms

When the system determines that this fault condition is met, drivers may observe the following specific functional anomalies or instrument feedback phenomena during driving:

• Significantly Reduced A/C Cooling Efficiency: Unable to accurately obtain evaporator surface temperature, the air conditioning system may enter protection mode, resulting in normal air volume at the outlet but lack of cold low-temperature air.
• Dashboard Warning Light On: The vehicle Instrument Cluster usually activates an "A/C Fault" or a general power management system warning icon, indicating to the driver that current thermal management function is limited.
• Automatic Climate Control Adjustment Failure: Electronic fan speed and compressor relay may not be able to perform closed-loop control based on set temperature, leading to the system switching to open-loop operation or non-operation.

Core Fault Cause Analysis

Based on fault logic architecture, the root causes of this abnormal signal are generally categorized into hardware or logical defects in the following three dimensions:

• Wiring or Connector Fault: This is the most common physical connection failure type. It includes wires between the sensor and control unit being open circuit, loose contact, shorted to ground or power, as well as terminal corrosion, pin back, and other mechanical connection issues.
• Evaporator Temperature Sensor Failure: The temperature sensing element (thermistor) inside the sensor body is burnt out or internal structure damaged, preventing it from forming an effective resistance value change at specific temperatures, thereby putting the signal line in an open circuit state.
• Left Domain Controller Fault: As the signal receiving and processing end, the analog input channel of the Left Domain Controller may have hardware damage, internal pull-up resistor failure, or software logic verification errors, causing normal signals to be misjudged as open circuit voltage.

Technical Monitoring and Trigger Logic

The system's self-diagnosis algorithm performs real-time calculations based on preset thresholds and operating conditions; its specific judgment mechanism is as follows:

• Monitoring Target: The system continuously reads the analog input signal voltage value (Sensor Output Voltage) of the evaporator temperature sensor to determine if circuit impedance is within the normal range.
• Fault Trigger Threshold: Within a specific sampling cycle, if it detects that the sensor output voltage value satisfies the inequality $V_{signal} > 4.95V$, an open circuit abnormality is determined. This voltage level far exceeds the expected working interval of the normal voltage divider circuit, indicating that the signal line has lost load or is at high impedance floating.
• Specific Trigger Condition: The activation of the fault only occurs when the vehicle ignition switch is in the ON position. The control unit needs to establish a reference ground and initialize input ports under the ignition powered-on state, ensuring monitoring is conducted while the system is powered on and entering normal operating cycles.

This judgment logic ensures that after ignition start-up, if the physical temperature feedback link cannot provide an effective signal, the system will record a fault code and restrict actions of relevant actuators to prevent equipment damage or uncontrollable functionality.