AU
B110A

This DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2 — Atto 3

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 — Atto 3
  • 1PM2.5 sensor internal circuit fault or module damage, preventing CAN signal transmission or transmitting 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 CAN_H and CAN_L circuits, or connector pin back-out, oxidation, or poor contact.
  • 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 the VDS or ED400 diagnostic tool to read all fault codes and freeze frame data. Confirm whether B110A is an active or history fault, and check for accompanying U-series 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 box air intake) 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 (should be less than 1Ω) 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 2.5-3.5V, and CAN-L to ground should be 1.5-2.5V. Power off the vehicle and measure the terminating resistance; it should be approximately 60Ω (disconnect the battery negative terminal during measurement to prevent parallel circuit interference).
  • 5
    Check wiring harness continuity, focusing on the connection between the instrument panel harness and body harness (near the CJB). Check for open circuits, poor connections, or insulation damage.
  • 6
    Replace the PM2.5 sensor (part number: SCE-8125400 or B23-8125400) to cross-check and observe whether the fault transfers.
  • 7
    If the sensor is normal, check the CAN communication line 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 typically in the 0x3A0-0x3AF range) to confirm 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 Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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]