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B2A4F11

DTC B2A4F11 indicates a short to battery in the signal circuit of the air conditioning system high-pressure line pressure sensor — Qin Plus

Thermal Management System

DTC B2A4F11 indicates a short to battery in the signal circuit of the air conditioning system high-pressure line pressure sensor.

In BYD new energy vehicle thermal management systems, a 5V reference voltage typically powers this sensor.

The sensor outputs a 0.5–4.5V analog voltage signal reflecting the refrigerant high-side pressure (normal range approximately 0.8–2.8V, corresponding to 0.3–3.0MPa).

The ECU logs a short to battery when it detects the sensor signal voltage remaining above 4.8V or near the reference supply voltage (5V) for longer than the calibrated time (typically over 200ms).

This fault prevents the air conditioning ECU from accurately reading high-side pressure data and triggers system protection strategies: disabling the electric compressor and suspending cooling/heating functions.

In severe cases, the system may limit vehicle power output to prevent loss of thermal management control.

The short circuit can occur within the sensor, the wiring harness connector, or the internal ECU sampling circuit.

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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1Damaged high-pressure sensor wiring harness insulation contacts nearby 12V power wires (such as the compressor controller power supply or PTC heater power wire), causing a short circuit. This commonly occurs at harness bend points such as the engine compartment firewall and fender liners.
  • 2Pressure sensor internal integrated circuit failure; internal breakdown between the signal output terminal and power input terminal. Typically occurs after prolonged vehicle operation in high-temperature environments or abnormal refrigerant pressure shocks.
  • 3Air conditioning controller (ECU) internal signal sampling circuit fault, abnormal pull-up resistor, or damaged chip input stage causing false detection of a sensor short circuit.
  • 4Improperly securing the wiring harness or missing retaining clips during repairs, causing the harness to chafe against sharp metal parts and sustain damage, or mistakenly splicing the sensor signal wire into a constant power circuit during modifications.
  • 5Connector terminal back-out or corrosion from water ingress causes a short circuit between the power terminal (Pin 1) and the signal terminal (Pin 3). This typically occurs in vehicles driven through water or after washing the engine compartment.
What To Do
  • 1
    Safety Preparation: Set the vehicle to OFF, disconnect the 12V battery negative terminal, wait 5 minutes to ensure the high-voltage system de-energizes, wear insulated gloves and safety goggles, and confirm the high-voltage interlock circuit is disconnected.
  • 2
    Fault confirmation: Connect the VDS2000/VDS3100 diagnostic tool and read the air conditioning system fault codes. Confirm B2A4F11 is a current fault (Active). Record freeze frame data (ambient temperature, battery temperature, compressor speed, etc.) and analyze the operating conditions when the fault occurred.
  • 3
    Circuit check: Open the front hood and locate the high-pressure line pressure sensor (at the electric compressor outlet or condenser inlet pipe). Disconnect the sensor 3-pin connector, turn the ignition switch ON (do not start), and measure the voltage between the sensor harness-side signal wire (usually Pin 2) and ground. If the voltage is 5V or 12V, it indicates a short to power in the harness; if it is 0V, replace the sensor.
  • 4
    Wiring harness inspection: If the signal wire has abnormal voltage, inspect the harness sleeve along its routing. Focus on the firewall pass-through, the harness bundle near the compressor controller, and the area near the front compartment fuse box. Check for damage, scorch marks, or melting. Use a multimeter on the continuity setting to measure continuity between the signal wire and the constant power fuse terminals in the fuse box.
  • 5
    Insulation repair: Upon locating the damage, separate the shorted wiring harness. Wrap each damaged wire individually with high-temperature tape (125°C or above). Reinstall the corrugated conduit and retaining clips. Maintain a clearance of more than 50mm from the power cable. Install a wiring harness protective sleeve if necessary.
  • 6
    Component verification: Measure the resistance of the new sensor or repaired wiring. Signal wire to ground resistance must exceed 10MΩ. Resistance between the sensor power supply (Pin 1) and signal (Pin 2) must be 1.5-3.0kΩ (varies with pressure). Confirm no short circuit to power exists before connecting the sensor.
  • 7
    System reset: Clear the fault code and turn on the A/C switch. Verify the 'high-pressure line pressure' value in the data stream displays correctly (0.8-2.5V corresponds to actual pressure). Check that the compressor engages normally. Perform a 10-minute road test to confirm the fault code does not return and cooling performance is normal.
Real-World Cases
BYD DTC AI Analysis

Song MAX DM: Intermittent Air Conditioning Failure Due to Wiring Harness Wear

✓
2018 Song MAX DM, 42,000 km. Owner reported the A/C suddenly stopped working after high-speed driving; the dash displayed 'A/C System Fault'. Scanned DTC B2A4F11 (current). Checked the high-pressure sensor connector: signal wire voltage measured 5.02V (abnormal). Traced the harness to the right front fender liner and found the sensor wiring had been chafing against the PTC heater power cable (12V) due to a dislodged retaining clip, wearing through the insulation and causing a short. Repaired the harness, re-secured it with waterproof cable ties, and cleared the fault.
BYD DTC AI Analysis

BYD Qin Pro EV: Sensor Internal Breakdown After Fast Charging

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2019 BYD Qin Pro EV. AC stopped cooling after 60kW fast charging. DTC B2A4F11 present. Sensor 5V supply normal; signal line resistance to ground was 0.8Ω (internal short). Replaced high-pressure line pressure sensor. Old sensor showed breakdown between internal piezoresistor and signal circuit. Fast charging caused battery cooling system high-pressure side surge; sensor quality defect led to internal breakdown. Installed OEM sensor; pressure data stream normal. Fault resolved.
BYD DTC AI Analysis

Connector Corrosion and Short Circuit Case in Flood-Damaged Vehicle

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2017 Qin EV300. Air conditioning inoperative after driving through standing water during a typhoon; DTCs B2A4F11 and B2A4E13 stored (open/short alternating). Removed the front bumper and found water stains and verdigris inside the high-pressure sensor connector. Electrolytic corrosion caused micro-shorting between terminals. Cleaned the connector terminals, flushed with electronic cleaner, dried with compressed air, and applied conductive grease. Insulation resistance tested normal. Advised customer to replace the seal and verify the wading depth record to avoid warranty disputes.
BYD DTC AI Analysis

Wiring harness incorrectly routed after accident repair

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2019 Song MAX. Three months after front collision repairs, the air conditioning intermittently stopped working. The diagnostic scanner showed historic fault code B2A4F11. Inspection revealed that during the accident repairs, the workshop failed to secure the front-compartment harness correctly, trapping the high-pressure sensor harness between the radiator support and body. Long-term vibration caused the harness to chafe through and contact a constant-power line. Re-routed the wiring, secured it with factory harness clips, repaired the damaged conductors, and restored standard routing. The fault has not recurred. This case demonstrates the importance of correct harness routing after accident repairs.
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.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.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.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.
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.