AU
B2A6700

This DTC indicates the Electric A/C Compressor (EAC) fails to establish normal speed or pressure after multiple consecutive start attempts following a start command — Atto 3

Thermal Management System

This DTC indicates the Electric A/C Compressor (EAC) fails to establish normal speed or pressure after multiple consecutive start attempts following a start command.

The system logs a start failure fault.

The root cause is the compressor controller failing to provide a valid speed signal within the specified time (typically 2-3 seconds) or failing to build torque.

On plug-in hybrid (DM) models, an electric compressor failure prompts the system to start the engine to drive the mechanical compressor (Belt-driven Compressor) as a backup cooling solution, triggering DTC B2A6700.

This fault causes a complete loss of A/C cooling capacity, which is particularly severe in pure electric mode.

Additionally, because the BYD thermal management system couples the battery chiller (Chiller) with the A/C system, a prolonged fault can cause power battery thermal management failure, triggering power limits or even high-voltage interlock disconnection.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Electric compressor high-voltage power supply fault: Causes include a blown compressor fuse in the high-voltage distribution box, poor contact in the high-voltage interlock loop (HVIL), burnt main negative/main positive contactors, or a damaged IPM module on the compressor internal motor drive board, preventing the compressor from receiving sufficient high-voltage DC power (typically 320V-750V).
  • 2Compressor mechanical seizure or motor fault: Internal scroll wear causing seizure, motor permanent magnet demagnetization, bearing seizure, or compressor oil deterioration causes excessive start-up torque, triggering controller overcurrent protection and resulting in start-up failure.
  • 3Low-voltage control communication fault: LIN bus or CAN bus communication interruption (between BMS, VCU, and compressor controller), abnormal wake-up signal, or Enable signal circuit open or shorted to ground, preventing the compressor controller from receiving the correct speed command.
  • 4Refrigerant pressure protective shutdown: Severely insufficient system refrigerant (leak) causes excessively low pressure on the low-pressure side, or excessive refrigerant/poor condenser heat dissipation causes excessively high pressure on the high-pressure side, triggering the pressure switch protection to prevent compressor startup.
  • 5Thermal Management System (TMS) controller or A/C controller software bug: Controller internal program logic error falsely reports a startup failure; or the algorithm threshold for deviation between the compressor target speed and actual control value is overly sensitive.
What To Do
  • 1
    Diagnostic tool reading and freeze frame analysis: Use VDS2000 or Launch X431 to read all fault codes. Check for accompanying high-voltage interlock faults (P0A0D, P0A0E) or insulation faults (P1A00 series). Record the data stream for ambient temperature, battery SOC, compressor target speed, and actual speed at the time of the fault.
  • 2
    High-voltage safety check and insulation test: Disconnect the manual service disconnect (MSD). Wait 5 minutes for high-voltage discharge. Use a megohmmeter to measure the electric compressor high-voltage harness insulation resistance to ground (standard: >20MΩ). Inspect the high-voltage connectors for burn marks or backed-out pins. Measure high-voltage interlock circuit continuity.
  • 3
    Low-voltage circuit and communication check: Disconnect the compressor low-voltage connector and measure the pins: constant power (B+) should be 12V, ground (GND) resistance <0.1Ω, LIN line voltage approximately 9-11V (dynamic), and CAN-H/CAN-L voltage to ground approximately 2.5V. Use an oscilloscope to check the LIN bus waveform for distortion.
  • 4
    Refrigerant pressure and system sealing check: Connect a manifold gauge set and check the static pressure (R134a: approx. 0.6-0.8 MPa at 25°C). If the pressure is too low, evacuate the system using a vacuum pump, hold vacuum for 30 minutes, and locate leaks using an electronic leak detector (common leak points include the compressor shaft seal and high/low-pressure ports).
  • 5
    Compressor operation test and current monitoring: Restore the high-voltage connection, enter the scan tool actuator test mode, and gradually increase the compressor speed (1000rpm→3000rpm→6000rpm). Use a clamp meter to monitor the high-voltage current. Normal start-up current should be <15A and rise steadily. If the current is >40A, immediately cut the power. If the current exceeds 40A or oscillates, the compressor assembly is faulty.
  • 6
    Controller software update and replacement: If all above checks are normal, update the Thermal Management System (TMS) controller and compressor controller to the latest software version. If the fault persists, replace the electric compressor assembly (Note: After replacement, add the specified ND-OIL8 refrigerant oil or equivalent, and perform the standard refrigerant charge).
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM: Backed-out HVIL pin causing intermittent no-start

✓
Intermittent A/C not cooling with DTCs B2A6700 and P0A0D (high voltage interlock fault). Found a backed-out pin in the HVIL circuit of the electric compressor high voltage connector; contact failed over bumps. Re-crimped the pin and applied conductive grease. Fixed. Common on 2018–2019 Qin Pro models due to weak retaining clips in early high voltage connector designs.
BYD DTC AI Analysis

IGBT module inside Qin EV300 compressor burnt out, causing complete failure.

✓
At 80,000 km, the AC failed completely. Scan tool showed DTC B2A6700. During actuator testing, the compressor did not respond and high-voltage side current read zero. Disassembled the compressor controller and found the internal IGBT power module burned out with visible burn marks on the driver board. Replaced the electric compressor assembly (part number: BC28-8103010) and refilled with 150 ml PAG 46 compressor oil and 450 g R134a refrigerant per specification. Fault resolved.
BYD DTC AI Analysis

Minor refrigerant leak triggered low-pressure protection, preventing startup

✓
Poor AC cooling in high summer temperatures. DTC B2A6700 logged. Data stream showed compressor stopped within 2 seconds of engagement, low-side pressure dropping below 0.15 MPa. Vacuum hold test and fluorescent leak detection found a minor leak at the battery cooler (Chiller) connection. Repaired the leak, replaced the receiver drier, evacuated and recharged the system. Pressures normalized (low side 0.2–0.3 MPa, high side 1.4–1.6 MPa). Fault resolved.
BYD DTC AI Analysis

LIN bus interference caused compressor controller communication fault.

✓
Aftermarket audio installation caused intermittent AC failure. Stored DTC B2A6700 with multiple LIN slave node communication faults. Found modified amplifier power wiring running parallel to the AC compressor LIN harness, causing electromagnetic interference. Re-routed wiring to separate power and signal lines (>30 cm apart) and installed a ferrite core filter on the compressor LIN line. Restored communication; fault has not reoccurred.
BYD DTC AI Analysis

Outdated thermal management controller software caused false fault detection.

✓
The 2019 Qin Pro EV frequently set DTC B2A6700 in cold conditions (-5°C), but the compressor ran normally. Live data revealed the controller was overly sensitive to compressor speed overshoot. Upgraded the TMS controller software to the latest version (3.00.15 or above) via VDS2000, adjusting the startup failure threshold. The fault cleared. This is BYD's official software optimisation fix.
Other Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.
Common problems reported for Atto 3 →Atto 3 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.