AU
B2A0813

DTC B2A0813 indicates an open circuit in the air conditioning system evaporator outlet refrigerant temperature sensor (PT sensor) circuit — Atto 8

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.

The B2A0813 fault code on the Atto 8 indicates an open circuit in the air conditioning evaporator outlet refrigerant temperature sensor circuit. This is a high-severity fault because it can limit or stop cooling and affect battery or motor heat management. Common causes include a failed sensor thermistor or loose/damaged wiring connectors near the evaporator. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 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 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 harness, or rodents gnawing the wiring and interrupting the circuit.
  • 4Bent, corroded, or oxidized sensor pins, common after driving through water or long-term use 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 supply missing), interrupting the sensor power supply.
What To Do
  • 1
    Read fault codes using the BYD VDS2000/VDS6000 diagnostic tool. Confirm B2A0813 is a current (Active) fault, not a history fault. Record freeze frame data (ambient temperature, evaporator temperature values, etc.).
  • 2
    Visually inspect the appearance of 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. Use a multimeter to measure the resistance between the two sensor terminals. The standard value at 25°C is 10kΩ±5%. Replace the sensor if the reading is OL (infinite). Also measure the voltage between the power supply terminal and ground; the voltage should be 5V±0.25V.
  • 4
    Perform a circuit continuity test: Measure the continuity of the signal wire and ground wire respectively from the sensor connector to the HVAC ECU connector (usually located behind the dashboard or glove box). Resistance should be <1Ω. Measure the insulation resistance to ground; it should be >10MΩ.
  • 5
    Check the HVAC ECU connector for backed-out pins, corrosion, or enlarged cavities. 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 (Part number reference: EA-8123456 for ATTO 3, TA-1234567 for Qin EV, etc.; confirm based on specific vehicle model). Apply adequate silicone grease to ensure 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). 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 Atto 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 overview →
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.