AU
B2A0813

DTC B2A0813 indicates an open circuit in the air conditioning system evaporator outlet refrigerant temperature sensor (PT sensor) circuit — Atto 3

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 — Atto 3
  • 1Aging or physical damage to the thermistor element inside the sensor body causes an open circuit, common in high-mileage vehicles (>80,000 km) or vehicles operating long-term in 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 interrupting the circuit.
  • 4Bent, corroded, or oxidized sensor pins, common after driving through water or long-term operation in high-humidity areas, causing infinite contact resistance between the pins and socket.
  • 5Air conditioning control unit (HVAC ECU) internal signal processing circuit fault or abnormal reference voltage output (5V power supply missing), interrupting the sensor power supply.
What To Do
  • 1
    Use the BYD VDS2000/VDS6000 diagnostic tool to read fault codes. Confirm B2A0813 is a current (Active) fault, not 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. Focus on the harness protective sleeve at the firewall pass-through.
  • 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 is 10kΩ±5%. If the multimeter displays OL (infinite), replace the sensor. Also measure the voltage between the power supply terminal and ground; the voltage must be 5V±0.25V.
  • 4
    Perform a circuit continuity test: Measure the continuity of the signal wire and the ground wire individually from the sensor connector to the HVAC ECU connector (usually located behind the dashboard or glove box). Resistance should be <1Ω. Measure insulation resistance to ground; resistance should be >10MΩ.
  • 5
    Check the HVAC ECU connector for backed-out pins, corrosion, or enlarged pin holes. If necessary, use a 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 based on the specific vehicle model). Apply an appropriate amount of silicone grease for proper heat transfer.
  • 7
    Reconnect all connectors and 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. Verify it drops normally during cooling (typically to 2-8°C) to confirm fault resolution.
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 Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.