AU
B2A2F09

DTC B2A2F09 indicates the air conditioning thermal management system detected abnormal refrigerant line pressure — Qin Plus

Thermal Management System

DTC B2A2F09 indicates the air conditioning thermal management system detected abnormal refrigerant line pressure.

Specifically, the high-pressure side pressure sensor reading falls outside the normal range (too high or too low).

This fault involves the electric compressor high-pressure line monitoring circuit.

The system triggers the fault when the pressure sensor detects a high-pressure side pressure > 3.2 MPa (overpressure protection) or < 0.2 MPa (underpressure protection).

This fault activates the air conditioning system safety protection mechanism and forces an electric compressor shutdown to prevent pipe rupture or compressor dry running, resulting in a loss of cooling.

In BYD new energy vehicles with highly integrated thermal management systems, this fault may also impair the battery cooling function, triggering vehicle thermal management power derating protection.

5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1High-pressure line pressure sensor body damage or installation damage (stripped threads or aging seal ring causing poor internal circuit contact)
  • 2Pressure sensor wiring harness circuit fault (B13-2 pin signal wire open or shorted to ground, or abnormal 5V reference voltage/ground circuit)
  • 3Abnormal refrigerant charge (system leak causing insufficient refrigerant and low pressure, or overcharging causing excessive high-side pressure)
  • 4Reduced condenser heat dissipation efficiency (external dirt blockage, electronic fan speed control module fault, or deformed cooling fins causing an abnormal rise in high-side pressure)
  • 5Expansion valve stuck or receiver-drier blocked (causes abnormal pressure difference between high- and low-pressure sides; sensor detects extreme pressure values)
What To Do
  • 1
    Use the VDS2000 diagnostic tool to read the fault code and freeze frame data. Record the specific pressure value, ambient temperature, and compressor speed at the time of the fault to determine if the high-side pressure is too high or the low-side pressure is too low.
  • 2
    Perform a static pressure test: Let the vehicle sit for 2 hours, then measure the high and low-side pressures. The standard value is 0.6-0.8 MPa (at 25°C ambient temperature). A significant deviation indicates an abnormal refrigerant charge.
  • 3
    Check the physical condition of the high-pressure sensor: disconnect the battery pack negative terminal, unplug the sensor connector, check the pins for oxidation and the threads for damage, and measure the sensor resistance (normal: 1.5-2.5kΩ).
  • 4
    Measure the sensor circuit: Turn the ignition switch to ON and measure the connector terminal voltage (reference voltage 5V±0.25V, signal voltage 0.5-4.5V varying with pressure, ground resistance <1Ω).
  • 5
    Check the condenser and cooling system: Visually inspect the condenser surface for foreign object blockage, perform the electronic fan active test, and confirm normal operation at low and high speeds.
  • 6
    Perform dynamic pressure test: Reconnect wiring, start air conditioning system, and observe pressure gauge. Normal high pressure is 1.5-2.5MPa (ambient temperature 25°C). If pressure rapidly rises above 3.0MPa, check expansion valve and lines for blockages.
  • 7
    If the sensor is faulty, replace the high-pressure pipe assembly (on some models, the sensor is integrated with the pipe). Replace the sealing ring and install to the specified torque (usually 15-20 N·m).
  • 8
    Evacuate the system (≥ 30 minutes, vacuum ≤ -0.1 MPa), charge refrigerant to the amount specified on the nameplate (usually 450-550 g), and use a leak detector to confirm no leaks.
  • 9
    Clear the fault code and perform a 15-minute road test. Monitor the 'ACP_HighPressure' value in the data stream to verify it is within the normal range and confirm the fault does not recur.
Real-World Cases
BYD DTC AI Analysis

Thread damage to the high-pressure sensor caused air-conditioning failure on a BYD e5

✓
2017 BYD e5 300, 80,000 km. Complete AC cooling failure. Scanned with VDS2000: DTC B2A2F09. Live data showed high-side pressure at 0.12 MPa (abnormally low), low-side at 1.72 MPa, static pressure at 1.60 MPa (normal). Found no voltage output from pin 2 of the high-pressure sensor connector B13. Removed the sensor; stripped threads from previous improper repair caused poor internal circuit contact. Replaced the high-pressure line assembly (including pressure sensor) and recharged refrigerant. High-side pressure returned to 2.1 MPa, AC cooling normal. Cleared fault codes.
Original source ↗
BYD DTC AI Analysis

BYD Qin A/C pressure sensor circuit open

✓
2018 BYD Qin PRO DM. Instrument cluster showed "Thermal Management System Fault." Scanned and found DTC B2A2F09. The pressure sensor harness between the AC compressor and control panel had chafed through at the firewall from vibration, causing an open circuit. No 5V reference at the sensor connector. Resoldered the break and applied waterproof insulation. Restored continuity; sensor signal voltage returned to normal (1.8V corresponding to 1.6MPa pressure). Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Qin low voltage supply abnormality triggered false pressure monitoring warning

✓
2019 BYD Qin EV. Vehicle wouldn't start; multiple warning lights on the dash. Scanned multiple systems and found DTC B2A2F09 among others. Diagnosis: 12V battery at 8.5V. Severe undervoltage caused unstable power to the Vehicle Control Unit (VCU) and Air Conditioning Control Module (ACU), resulting in data communication errors and a false AC line pressure fault. Charged the 12V battery to 12.6V with a dedicated charger and cleared all DTCs. Vehicle started normally; B2A2F09 did not return. Recommended replacing the aging 12V battery.
Original source ↗
BYD DTC AI Analysis

BYD Song MAX: Poor condenser cooling caused high-pressure side over-pressure protection

✓
2019 BYD Song MAX DM. Air conditioning intermittently cut out after high-speed summer driving, storing DTC B2A2F09. Freeze frame data showed high-side pressure at 3.8 MPa during the fault (severely exceeded limit). Found the condenser covered in willow fluff and dust, and the cooling fan high-speed mode inoperative (damaged speed control module). Thoroughly cleaned the condenser fins and replaced the fan speed control module. High-side pressure now stable at 2.2 MPa and the air conditioning works continuously. Fault cleared.
BYD DTC AI Analysis

Refrigerant leak caused low pressure on the low side of the BYD Qin EV

✓
2017 BYD Qin EV300. AC cooling gradually weakened until complete failure, with DTC B2A2F09 set. Static pressure test read only 0.25 MPa (significantly low). Halogen leak detector found the high-pressure line quick-connect seal ring degraded and leaking. Recovered remaining refrigerant, replaced the line seal ring and desiccant, re-evacuated and charged 480g R134a. After startup: low pressure 0.25 MPa, high pressure 1.8 MPa, pressure sensor signal voltage 1.2 V. System operates normally; fault code cleared.
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.