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 3

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 3
  • 1Internal open circuit in the sensor body: Prolonged exposure to high-temperature, high-pressure refrigerant ages the plate heat exchanger refrigerant temperature sensor (NTC thermistor). This breaks the internal resistor element, causing infinite resistance.
  • 2Loose harness connector or backed-out pins: The sensor connector in the high-temperature, high-vibration area of the front compartment (usually a 2-pin plug) loosens due to a failed retaining clip or improper assembly, or female terminals back out or spread due to repeated plugging and unplugging.
  • 3Physical damage to the wiring harness: Vibration and friction damage the insulation and cause internal copper wire fatigue fractures where the harness section between the engine compartment and the chassis passes through the firewall, frame mounting holes, or along the battery pack edges; or repair work crushes or cuts the wiring harness.
  • 4Refrigerant leak corrosion: An aging sealing ring at the plate heat exchanger connection causes a slight refrigerant leak. A mixture of liquid refrigerant and refrigerant oil seeps into the sensor threaded connection, corroding the internal sensor circuit and causing an open circuit.
  • 5Connector oxidation: In water 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 BYD dedicated diagnostic tool to read the DTC freeze frame data. 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 fault codes (e.g., electronic expansion valve or compressor faults).
  • 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. Focus 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 normal temperature (25°C), the standard resistance is typically 2kΩ-10kΩ (refer to the repair manual for exact specifications). Replace the sensor if the reading shows infinity (OL) or 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, terminal push-out, deformation, or enlarged sockets. Clean the pins 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, first recover the refrigerant from the air conditioning system. Use the special tool to remove the old sensor (note the thread seal). Replace the sealing washer, install the new sensor, and tighten to the specified torque (typically 15-20 N·m). Evacuate the system for at least 30 minutes to a vacuum below -95 kPa. Recharge with the standard amount of refrigerant and refrigerant oil.
  • 7
    Function verification and road test: Clear the fault code, 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 fast charging test. Confirm the battery thermal management system engages normally and does not generate 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 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.