AU
B2A2F09

DTC B2A2F09 indicates the air conditioning thermal management system detected abnormal refrigerant line pressure — Atto 8

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.

The B2A2F09 fault code on the Atto 8 indicates abnormal refrigerant pressure in the air conditioning high-pressure line, either too high or too low. This medium-severity fault can shut down the electric compressor, causing loss of cooling and possibly reducing battery cooling performance. Common causes include a damaged pressure sensor or wiring faults in the signal, 5V reference, or ground circuits. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 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 circuit, short to ground, or abnormal 5V reference voltage/ground circuit)
  • 3Abnormal refrigerant charge amount (system leak causing insufficient refrigerant and excessively low pressure, or overcharging causing excessively high pressure on the high-pressure side)
  • 4Reduced condenser heat dissipation efficiency (external debris blockage, electronic fan speed control module failure, or deformed cooling fins causing abnormal high-side pressure increase)
  • 5Stuck expansion valve or clogged receiver-drier (causing 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 when the fault occurred to determine whether the high pressure is too high or the low pressure is too low.
  • 2
    Perform a static pressure test: Allow the vehicle to sit for 2 hours, then measure the high and low-side pressures. The standard value is 0.6-0.8MPa (at 25℃). 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, inspect the pins for oxidation and the threads for damage, and measure the sensor resistance (normal: 1.5-2.5 kΩ).
  • 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 blockages, perform the electronic fan active test, and confirm normal operation at low and high speeds.
  • 6
    Perform a dynamic pressure test: reconnect the wiring, start the air conditioning system, and observe the pressure gauge. Normal high-side pressure is 1.5-2.5MPa (ambient temperature 25°C). If pressure rapidly rises above 3.0MPa, check the expansion valve and lines for blockages.
  • 7
    If the sensor is faulty, replace the high-pressure pipe assembly (some models integrate the sensor with the pipe). Replace the sealing ring and install the assembly to the specified torque (usually 15-20 N·m).
  • 8
    Evacuate the system (≥30 minutes, vacuum ≤-0.1MPa), charge refrigerant to the amount specified on the nameplate (usually 450-550g), 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 confirm it is within the normal range and 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

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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 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.