AU
B2A0F13

This fault code indicates an open circuit in the refrigerant temperature sensor signal circuit at the inlet or outlet of the plate heat exchanger (chiller, battery cooler) — Atto 8

Thermal Management System

This fault code indicates an open circuit in the refrigerant temperature sensor signal circuit at the inlet or outlet of the plate heat exchanger (chiller, battery cooler).

The sensor is an NTC thermistor that monitors the temperature of the refrigerant exchanging heat with the battery coolant, serving as a key feedback component in the BYD thermal management system.

The ECU monitors this temperature to adjust the electronic expansion valve opening and electric compressor speed, precisely controlling the battery pack temperature.

When the ECU detects the sensor signal voltage continuously exceeding the upper threshold (typically the 5V reference voltage, indicating an open circuit), it sets an open circuit fault.

The thermal management system consequently loses precise control over battery cooling and heating.

This failure may trigger the battery thermal management protection strategy, forcing the vehicle into power limitation mode (limp mode), disabling fast charging, or triggering a high coolant temperature warning.

Extreme cases pose a risk of battery thermal runaway.

4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Internal open circuit in the sensor body: Long-term exposure to high-temperature, high-pressure refrigerant degrades the plate heat exchanger refrigerant temperature sensor (NTC thermistor), breaking the internal resistor element and causing infinite resistance.
  • 2Loose wiring harness connector or backed-out terminal pins: The sensor connector (usually a 2-pin plug) located in the high-temperature and vibration area of the front compartment comes loose due to a failed retaining clip or improper assembly, or the female terminal pins back out or terminal holes enlarge due to repeated connection and disconnection.
  • 3Physical damage to the wiring harness: Vibration and friction cause insulation damage and internal copper wire fatigue fractures in the engine compartment-to-chassis harness section where it routes through the firewall and frame mounting holes, or along the battery pack edge; or maintenance work crushed or cut the harness.
  • 4Refrigerant leak corrosion: An aging sealing ring at the plate heat exchanger connection causes a minor refrigerant leak. The mixture of liquid refrigerant and refrigerant oil seeps into the threaded sensor connection, corroding the internal sensor circuit and causing an open circuit.
  • 5Connector oxidation: In wading or high-humidity environments, poor sensor connector sealing causes pin oxidation or electrolytic corrosion, resulting in a high-resistance open circuit.
What To Do
  • 1
    Fault confirmation and freeze frame analysis: Use VDS or a dedicated BYD diagnostic tool to read the DTC freeze frame. Record the vehicle speed, battery temperature, ambient temperature, and air conditioning status at the time of the fault. Determine if the fault is current or historical. Check for accompanying thermal management system DTCs (e.g., electronic expansion valve fault, compressor fault).
  • 2
    Visual and wiring inspection: Raise the vehicle. Inspect the sensor at the plate heat exchanger (located in the front compartment, near the battery coolant pipes) for deformation or oil leaks. Trace the wiring harness routing and inspect for wear, damaged insulation, or burn marks, focusing on the firewall pass-through and harness retaining clips.
  • 3
    Sensor body resistance measurement: Disconnect the sensor connector and use a multimeter to measure the resistance across the sensor terminals. At room temperature (25°C), the standard resistance is typically 2kΩ-10kΩ (refer to the workshop manual for specific values). Replace the sensor if the reading shows infinity (OL) or if the resistance deviates significantly from the standard curve.
  • 4
    Harness continuity test: Disconnect the connector at the thermal management controller (or the relevant module integrated into the air conditioning controller). Measure the harness continuity resistance between the sensor plug and the controller. Resistance must be less than 1 Ω. Measure the resistance to ground; it must be greater than 10 MΩ (to rule out a short to ground). If an open circuit exists, repair or replace the harness.
  • 5
    Connector pin inspection: Inspect the male and female sensor connector pins for oxidation, blackening, push-out, deformation, or enlarged holes. Clean with electrical contact cleaner. If necessary, use a terminal removal tool to repair the pins or replace the connector housing. Verify the sealing ring is intact.
  • 6
    Sensor replacement and refrigerant system handling: If the sensor is faulty, recover the refrigerant from the air conditioning system. Use the special tool to remove the old sensor (note the thread seal). Install the new sensor with a new sealing washer and tighten to the specified torque (usually 15–20 N·m). Evacuate the system for at least 30 minutes to a vacuum below -95 kPa. Add the standard amount of refrigerant and compressor oil.
  • 7
    Function verification and road test: Clear the fault codes, start the vehicle, and turn on the A/C cooling mode. Read the data stream to verify the plate heat exchanger refrigerant temperature sensor value drops normally during compressor operation (normal range: -10°C to 50°C). Perform a DC fast charging test to confirm the battery thermal management system engages normally and the system generates no new fault codes.
Real-World Cases
BYD DTC AI Analysis

The Qin EV suddenly entered limp mode while driving, logging DTC B2A0F13.

✓
A 2019 BYD Qin EV with 82,000 km. Customer reported that while driving at highway speeds, the dashboard suddenly displayed "Power Limited, Please Park Safely" and the coolant temperature high warning light came on. Retrieved DTC B2A0F13 (current fault). Inspection found the plate heat exchanger refrigerant temperature sensor wiring harness had chafed against the metal edge of the front bulkhead penetration due to long-term vibration, wearing through the insulation and severing the copper conductors. Repair: Cut out the damaged harness section and soldered in high-temperature wire of the same specification (125°C minimum rating), applied double-layer heat shrink tubing, rerouted the harness and added a rubber grommet to prevent recurrence. Road tested after repair; live data showed normal refrigerant temperature and the fault cleared.
BYD DTC AI Analysis

Battery pack high temperature warning during fast charging; sensor internal open circuit

✓
2019 BYD Qin EV. After 10 minutes of fast charging, the dashboard displayed "Battery temperature too high" and charging power suddenly dropped below 5 kW. The scanner retrieved DTC B2A0F13; freeze frame data showed the refrigerant temperature at -40°C (default open-circuit extreme value) when the fault occurred. Sensor resistance read infinite, indicating an open circuit in the internal NTC thermistor. The sensor sits at the refrigerant outlet of the plate heat exchanger, operating under long-term high pressure (1.5–3.0 MPa) and temperature cycling. Replaced the sensor, then evacuated the AC system and recharged it with 450 g of R410a refrigerant. Post-repair fast charging test confirmed the battery temperature stayed below 35°C; fault resolved.
BYD DTC AI Analysis

Intermittent DTCs after accident repair, loose connector

✓
A Qin EV involved in a front-end collision was repaired at a dealership. Afterward, the vehicle intermittently set DTC B2A0F13 while driving, accompanied by intermittent AC cooling loss. Technicians found the plate heat exchanger temperature sensor connector had not fully seated during the collision repair. While it appeared connected externally, the male and female terminals inside had poor contact, causing momentary open circuits over bumps. Repair: Disconnected the connector and found the female contacts slightly enlarged. Resized the terminals using a special tool, applied conductive paste, and reconnected until a distinct click confirmed the lock. Secured the harness to the bracket with a cable tie to eliminate stress. Monitored for one week with no fault recurrence.
BYD DTC AI Analysis

Corrosion of the sensor connector on the water-damaged vehicle caused an open circuit

✓
A Qin EV in the southern region threw code B2A0F13 on startup the day after driving through floodwater. Inspection revealed the vehicle had waded deeper than the wheel centers, submerging the front compartment wiring harness. The plate heat exchanger temperature sensor connector (located in the lower front compartment) contained standing water, with pins showing green copper corrosion and white electrolytic corrosion that caused an open circuit. Repair: Disconnected the battery negative terminal and thoroughly cleaned the connector using precision electronic cleaner and ultrasonic cleaning, then dried it. The corrosion had damaged the pin plating, so replaced the sensor harness assembly (including the connector) to eliminate any risk of recurrence. Applied waterproof silicone grease to other low-position connectors for protection.
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.