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 — Qin Plus

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.

The B2A6700 fault code on the Qin Plus indicates the electric A/C compressor cannot start correctly or build normal speed or pressure after repeated attempts. Severity is medium, but cooling may be lost and battery thermal management can be affected. Common causes include abnormal high-voltage power supply to the compressor or internal compressor seizure or motor failure. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from 5 recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Abnormal high-voltage power supply to the electric compressor: 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. This prevents the compressor from receiving sufficient high-voltage DC power (typically 320V-750V).
  • 2Compressor mechanical seizure or motor fault: Internal scroll plate wear causing seizure, motor permanent magnet demagnetization, bearing seizure, or refrigerant oil deterioration causes excessive starting torque, triggering controller overcurrent protection and start-up failure.
  • 3Low-voltage control communication fault: LIN bus or CAN bus communication interruption (between the BMS, VCU, and compressor controller), abnormal wake-up signal, or an open circuit or short to ground in the Enable signal line, preventing the compressor controller from receiving the correct speed command.
  • 4Refrigerant pressure protective shutdown: Severe system refrigerant shortage (leakage) 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 pressure switch protection to prevent compressor startup.
  • 5Thermal Management Controller (TMS) or A/C controller software bug: Internal controller 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
    Scan tool reading and freeze frame analysis: Use VDS2000 or Launch X431 to read all fault codes. Check for accompanying high-voltage interlock (P0A0D, P0A0E) or insulation (P1A00 series) faults. Record the ambient temperature, battery SOC, compressor target speed, and actual speed data streams at the time of the fault.
  • 2
    High-voltage safety inspection and insulation test: Disconnect the manual service disconnect (MSD). Wait 5 minutes for the high voltage to discharge. Use a megohmmeter to measure the insulation resistance to ground of the electric compressor high-voltage wiring harness (standard >20MΩ). Inspect the high-voltage connectors for burn marks or backed-out terminals. Measure the continuity of the high-voltage interlock circuit.
  • 3
    Low-voltage circuit and communication check: Disconnect the compressor low-voltage connector and measure the pin values: constant power (B+) should be 12 V, ground (GND) resistance <0.1 Ω, LIN line voltage approximately 9–11 V (dynamic), and CAN-H/CAN-L voltage to ground approximately 2.5 V. Use an oscilloscope to check the LIN bus waveform for distortion.
  • 4
    Refrigerant pressure and system leak check: Connect a manifold gauge set and check the static pressure (approx. 0.6-0.8 MPa at 25°C for R134a). If the pressure is too low, use a vacuum pump to evacuate the system, hold the vacuum for 30 minutes, and use an electronic leak detector to locate leaks (commonly found at 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, cut the power immediately. If the current exceeds 40A or oscillates, the compressor is faulty.
  • 6
    Controller software update and replacement: If all previous checks are normal, update the Thermal Management System (TMS) controller and the 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 charge the system with the standard refrigerant amount.)
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 Qin Plus Fault Codes
B1108For 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.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.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.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus 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.