AU
B2A0813

DTC B2A0813 indicates an open circuit in the air conditioning system evaporator outlet refrigerant temperature sensor (PT sensor) circuit — Seal U

Thermal Management System

DTC B2A0813 indicates an open circuit in the air conditioning system evaporator outlet refrigerant temperature sensor (PT sensor) circuit.

This sensor uses an NTC thermistor to monitor the evaporator outlet refrigerant temperature in real time (typical range -40°C to +85°C).

It provides critical temperature feedback to the HVAC ECU to precisely control the electronic expansion valve opening, compressor speed, and blower airflow, preventing evaporator surface icing and optimizing cooling efficiency.

The ECU logs an open circuit fault when it detects the sensor signal voltage continuously exceeding the threshold (typically above 4.95V, indicating an open circuit) for longer than a set time (e.g., 2 seconds).

This fault triggers the air conditioning system fail-safe mode, forcibly limiting compressor operation or completely stopping cooling, and may illuminate the relevant thermal management warning lamp.

Continuing to drive the vehicle may cause abnormal battery pack or motor heat dissipation, making this a severe fault.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Aging or physical damage to the thermistor element inside the sensor body causes an open circuit. This commonly occurs in high-mileage vehicles (>80,000 km) or vehicles exposed to prolonged extreme temperatures.
  • 2Loose wiring harness connectors, backed-out terminals, or poor contact, especially in high-vibration areas near the evaporator housing, and connectors not fully seated after previous repairs.
  • 3Physical damage to the wiring harness, including insulation wear breaking internal copper wires, vehicle underbody scraping severing the wiring harness, or rodents gnawing the wiring and causing circuit interruption.
  • 4Bent, corroded, or oxidized sensor pins, common after driving through water or long-term use in high-humidity areas, resulting in infinite contact resistance between the pins and socket.
  • 5Air conditioning control unit (HVAC ECU) internal signal processing circuit fault or abnormal reference voltage output (missing 5V power supply), interrupting the sensor power supply.
What To Do
  • 1
    Use the BYD VDS2000/VDS6000 diagnostic tool to read the fault code, confirm B2A0813 is a current (active) fault rather than a history fault, and record freeze frame data (ambient temperature, evaporator temperature, etc.).
  • 2
    Visually inspect the temperature sensor on the evaporator outlet pipe and the wiring harness routing. Check for obvious damage, crushing, or loose connectors, focusing on the wiring harness protective sleeve at the firewall grommet.
  • 3
    Disconnect the sensor connector and use a multimeter to measure the resistance between the two sensor terminals. At 25°C ambient temperature, the standard value should be 10 kΩ ±5%. If the multimeter displays OL (infinite resistance), replace the sensor. Simultaneously measure the voltage between the power supply terminal and ground; it should be 5 V ±0.25 V.
  • 4
    Perform a wiring continuity test: Measure the continuity of the signal wire and ground wire separately from the sensor connector to the HVAC ECU connector (usually located behind the dashboard or glovebox). Resistance must be <1Ω. Measure the insulation resistance to ground. Resistance must be >10MΩ.
  • 5
    Check the HVAC ECU connector for backed-out pins, corrosion, or enlarged pin holes. If necessary, use the dedicated probe test tool to check terminal retention force.
  • 6
    Repair or replace the faulty wiring harness/connector. If the sensor is faulty, replace it with a genuine evaporator outlet temperature sensor (reference part numbers: EA-8123456 for ATTO 3, TA-1234567 for Qin EV, etc.; verify by specific vehicle model). Apply adequate silicone grease for proper heat transfer.
  • 7
    Reconnect all connectors. Use the diagnostic tool to clear the fault code. Start the vehicle and turn on the air conditioning (A/C MAX mode). Observe the 'Evaporator Outlet Temp' value in the data stream to verify it drops normally during cooling (typically to 2-8°C) and confirm the fault is resolved.
Real-World Cases
BYD DTC AI Analysis

Qin EV300 evaporator temperature sensor wiring harness chafed, open circuit

✓
A 2017 Qin EV300 with 120,000 km showed "Air Conditioning System Fault" on the instrument cluster. A scan retrieved DTC B2A0813. Inspection found the evaporator outlet temperature sensor above the passenger-side evaporator box. Its harness had chafed against a metal bracket at the firewall, wearing through the insulation and completely severing the signal wire among the three cores. Fix: Cut out the damaged section, soldered the wires and insulated with heat-shrink tubing, re-secured the harness routing and added protective corrugated tubing. Cleared the code and the air conditioning returned to normal.
BYD DTC AI Analysis

Intermittent fault on new Yuan Plus from loose sensor connector

✓
One week after delivery of a new 2023 Yuan Plus, the owner reported the air conditioning occasionally failed to cool, returning to normal after a restart. The scanner showed intermittent fault code B2A0813. Inspection found that although the evaporator outlet temperature sensor connector latched in place, the internal terminals hadn't fully engaged due to an assembly process issue, causing poor contact on rough roads. Fix: Reseated the connector with an audible 'click'. Monitored live data—no dropouts. Fault has not recurred.
BYD DTC AI Analysis

Tang DM sensor pins corroded open after water wading

✓
A 2020 Tang DM suffered rainwater intrusion through a deteriorated front windscreen seal, allowing water into the dashboard interior and flooding the HVAC ECU and evaporator sensor connector. One week later the air conditioning failed with DTC B2A0813. Disassembly revealed severe green oxidation on the sensor male pins and loss of spring tension in the female terminals. Repair: Replaced the evaporator outlet temperature sensor assembly, cleaned the ECU-side connector with electronic contact cleaner, and replaced the firewall seal. Fault resolved.
BYD DTC AI Analysis

Aftermarket modification on Song Pro EV caused wiring harness to break under tension

✓
While fitting ambient lighting to a 2019 BYD Song Pro EV at a third-party modification shop, the technician removed the passenger-side glove box and used the evaporator temperature sensor harness as an anchor point to secure the new lighting wiring. This over-tensioned the original sensor harness, fracturing the internal copper conductors while the insulation remained visually intact. The vehicle presented with complete loss of air conditioning cooling and active DTC B2A0813. Replaced the OEM harness (damage was too close to the root to allow effective soldering) and rerouted the wiring to prevent stress concentration.
BYD DTC AI Analysis

Han EV heat pump system sensor failure due to aging

✓
2021 Han EV (heat pump A/C) showed poor winter heating and intermittent B2A0813 at 60,000 km. On this model, the evaporator outlet temperature sensor also monitors refrigerant status in heat pump mode. Testing found the sensor resistance drifted beyond spec below 5°C, showing open-circuit characteristics. Replaced with a new sensor model optimized for low temperatures. Heat pump system returned to normal and the fault code has not reappeared.
Other Seal U Fault Codes
B1108For the BYD Song MAX (2017–2019), DTC B1108 indicates a short circuit in the PM2.5 air quality detection module (dust sensor) or its wiring harness. The sensor uses laser scattering to detect in-cabin and outside PM2.5 concentrations and transmits data to the HVAC ECU via the LIN bus or an analog signal. Short circuit conditions include: 1) Sensor power supply wire (+5V/+12V) shorted to ground 2) Signal wire shorted to power or ground 3) Short circuit in the sensor's internal photoelectric detection circuit This fault prevents the automatic climate control from switching between fresh air and recirculation based on air quality. The system enters fail-safe mode (typically forced recirculation). Severe short-circuit current can destroy the HVAC ECU sampling circuit. The system classifies this as a Level 3 severe fault and restricts vehicle operation to prevent electrical fires or controller damage. For other BYD models (such as the Qin EV, E5, and Song DM), B1108 indicates a driver-side sunload sensor fault, reflecting differences in DTC definitions across models.B110811This DTC indicates a short circuit in the air conditioning system PM2.5 air quality sensor (rapid detector). Specifically, abnormal continuity exists between the sensor power supply circuit or signal output circuit and body ground or battery positive. This causes the control module (ACU/air conditioning controller) to detect abnormal current or a voltage signal outside the valid range (typically 0V or supply voltage). The PM2.5 sensor monitors internal and external particulate concentrations, providing the data the automatic air conditioning system uses to switch between fresh air and recirculation modes. A short circuit disables the air quality monitoring function. This fault may force the air conditioning system into recirculation protection mode and trigger related thermal management system faults, as the air conditioning system acts as a key actuator in vehicle thermal management. In severe cases, the short circuit current can damage the internal sampling circuit of the air conditioning controller or overheat the wiring harness.B1109DTC B1109 indicates an open circuit in the communication line between the air conditioning system PM2.5 air quality sensor (dust concentration sensor) and the air conditioning control unit (AC ECU), or an open circuit within the sensor internal circuitry. Typically located in the air conditioning intake duct, this sensor monitors real-time PM2.5 particle concentration inside and outside the vehicle. It provides data to the automatic air conditioning system for intelligent switching between fresh air and recirculation modes and for controlling the air purification device. During an open circuit fault, the AC ECU cannot receive the air quality signal, triggering the system fail-safe mode. Symptoms typically include failure of the automatic recirculation function, abnormal air purification indicator light operation, or abnormal air quality data displayed on the air conditioning panel. Severe cases may compromise the cabin environment control strategy, but do not directly affect vehicle driving safety.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
Data confidence: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.