AU
B110A

This DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2 — Seal 6 EV

Thermal Management System

This 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.

7
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1PM2.5 sensor internal circuit fault or module damage, resulting in failure to send CAN signals or transmission of error frames.
  • 2Open or short circuit in the sensor power supply circuit (constant B+ or IGN power), or a loose or oxidized ground point causing abnormal power supply.
  • 3Open circuit, short circuit, or short to ground/power in the CAN_H and CAN_L wiring, or connector pin back-out or poor contact due to oxidation.
  • 4Air conditioning control unit (ACU) CAN transceiver hardware fault, abnormal terminating resistance, or software communication protocol mismatch
  • 5Comfort CAN bus network interference or terminating resistor deviation (normally 60Ω), degrading signal integrity.
What To Do
  • 1
    Use a VDS or ED400 diagnostic tool to read the complete fault codes and freeze frame data. Confirm whether B110A is an active or history fault. Check for accompanying U-class communication fault codes (e.g., U0146, U0155).
  • 2
    Visually inspect the PM2.5 sensor (usually located inside the passenger-side dashboard or at the A/C unit air inlet) for external damage. Check the connector for looseness, oxidation, or water ingress, and inspect the wiring harness for damage.
  • 3
    Measure the sensor connector supply voltage (typically 12V ± 0.5V for Song MAX) and ground resistance (less than 1 Ω) to confirm the power supply and ground are normal.
  • 4
    Use a multimeter to measure the CAN line voltage: CAN-H to ground should be 2.5-3.5 V, and CAN-L to ground should be 1.5-2.5 V. Power off the vehicle and measure the terminal resistance, which should be approximately 60 Ω (disconnect the battery negative terminal during measurement to prevent parallel circuit interference).
  • 5
    Check wiring harness continuity, focusing on the connector between the instrument panel harness and the body harness (near the CJB). Inspect for open circuits, poor connections, and insulation damage.
  • 6
    Replace the PM2.5 sensor (part number: SCE-8125400 or B23-8125400) to cross-check and observe if the fault transfers.
  • 7
    If the sensor is normal, check the CAN communication circuit continuity at the air conditioning control unit terminal. If necessary, update the ACU software (version must be ≥V1.05) or replace the control unit.
  • 8
    After repair, clear the fault code, perform a road test, and monitor the CAN message stream (ID usually in the 0x3A0-0x3AF range) to verify the communication cycle and signal values return to normal.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

2018 Song MAX: Internal short in PM2.5 sensor brought down CAN bus

✓
The vehicle presented with inoperative automatic air purification. The scan tool read active DTC B110A. Found the PM2.5 sensor's internal CAN transceiver had shorted, causing CAN_H to short to ground (0.2 V). This disrupted the entire comfort CAN network and caused multiple modules to lose communication. Disconnected the sensor plug and the other modules resumed normal communication. Replaced the PM2.5 sensor, eliminating the fault and restoring normal CAN bus voltages (CAN-H: 2.7 V, CAN-L: 2.3 V).
BYD DTC AI AnalysisFrom Chinese market (translated)

2019 Song MAX: Worn dashboard wiring harness causing intermittent CAN signal interruption

✓
Owner reported intermittent automatic air conditioning mode failure. DTC B110A appeared intermittently, often triggered on rough roads. Inspection found the right-side dashboard wiring harness rubbing against a metal bracket, causing a partial fracture of the CAN_H wire core; contact resistance measured 5–50 ohms, fluctuating. Repaired the harness by soldering and applying heat-shrink tubing, rerouted and secured the harness to prevent rubbing. The fault has not recurred.
BYD DTC AI AnalysisFrom Chinese market (translated)

2017 Song MAX: Water ingress into connector caused oxidation and communication failure

✓
After water damage repairs, the vehicle stored DTC B110A and the air conditioning recirculation would not automatically switch. Inspection of the passenger-side PM2.5 sensor connector found visible water stains and verdigris (copper) corrosion, with reduced insulation resistance across the pins. Cleaned the connector terminals, treated them with WD-40 Precision Contact Cleaner, applied conductive grease, and sealed the connector with waterproof tape. After confirming normal CAN line continuity, cleared the fault code; the function was restored.
BYD DTC AI AnalysisFrom Chinese market (translated)

2018 Song MAX: Low ACU software version caused false communication fault.

✓
The new vehicle frequently set DTC B110A. Checked the wiring harness and sensor and found no faults. Most codes were historic. Consulted BYD technical service bulletin TSB-2020-AC-03: On this batch of vehicles, ACU software version V1.02 has insufficient fault tolerance for PM2.5 sensor communication, generating false faults during voltage fluctuations or rapid power-on. Upgraded ACU software to version V1.05. The fault code no longer appears; air quality monitoring functions normally.
BYD DTC AI AnalysisFrom Chinese market (translated)

2019 Song MAX: Worn dashboard wiring harness causing intermittent CAN signal interruption

✓
Owner reported intermittent failure of the automatic A/C mode. DTC B110A appeared intermittently, especially when driving on bumpy roads. Inspection found the wiring harness on the right side of the dashboard rubbing against a metal bracket, causing a partial break in the CAN_H wire core. Contact resistance fluctuated between 5-50 ohms. Repaired the harness by soldering the break and covering with heat-shrink tubing. Rerouted and secured the harness to prevent further rubbing. The fault has not recurred.
BYD DTC AI AnalysisFrom Chinese market (translated)

2017 Song MAX: Water ingress into connector caused oxidation and communication failure

✓
After water damage repairs, the vehicle set DTC B110A and the recirculation mode would not switch automatically. I found water ingress and verdigris corrosion inside the passenger-side PM2.5 sensor connector, reducing insulation resistance between pins. I cleaned the connector terminals, then treated them with WD-40 precision instrument cleaner. I applied conductive grease and waterproofed the connection. After verifying CAN bus continuity was normal, I cleared the fault code and normal function returned.
BYD DTC AI AnalysisFrom Chinese market (translated)

2018 Song MAX: Low ACU software version caused false communication fault.

✓
The new vehicle frequently set DTC B110A. Checked the wiring harness and sensor; no faults found. Most codes were history codes. Consulted BYD technical service bulletin TSB-2020-AC-03: ACU software V1.02 on this batch has insufficient fault tolerance for PM2.5 sensor communication, falsely triggering faults during voltage fluctuations or rapid power-on. Upgraded ACU software to V1.05. The DTC did not return, and air quality monitoring operated normally.
Other Seal 6 EV 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.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.
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. Sources: [1]