AU
B110811

This DTC indicates a short circuit in the air conditioning system PM2 — Atto 3

Thermal Management System

This 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.

3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1PM2.5 sensor internal circuit board short circuit (laser detection module or voltage regulator chip breakdown), commonly due to sensor water ingress or component aging.
  • 2Damaged sensor wiring harness insulation causing a short to ground or short to power, frequently occurring at vibration and chafing points such as the firewall pass-through hole and air conditioning housing edge.
  • 3Short circuit in the air conditioning controller (ACU) internal signal sampling circuit, causing a false sensor fault.
  • 4Water ingress or corrosion in the sensor connector (e.g., from vehicle wading or condensation soaking due to a blocked A/C drain hose), causing a short circuit between pins.
  • 5During repairs, accidental tool contact or an improperly secured wiring harness causes the sensor 5V reference power wire to short to the signal wire or ground wire.
What To Do
  • 1
    Use the BYD VDS diagnostic tool to read the complete fault information and freeze frame data, record the ambient temperature and air conditioning operating status at the time of the fault, and check for accompanying B11 series fault codes.
  • 2
    Locate the PM2.5 sensor installation position (on Qin series models, typically in the air intake duct downstream of the A/C filter/upstream of the blower, or under the passenger-side dashboard). Inspect the connector for signs of water ingress, terminal corrosion, or backed-out pins.
  • 3
    Disconnect the sensor connector and use a multimeter to measure the sensor-side resistance. Normal resistance is 1kΩ-100kΩ (depending on the specific model). If the resistance is close to 0Ω, replace the sensor. Measure the wiring harness side: the power supply pin to ground voltage must be 5V±0.25V (or 12V, depending on vehicle configuration), and the signal wire to ground resistance must be infinite. If the signal wire has continuity to ground, the wiring harness has a short circuit.
  • 4
    Inspect along the sensor harness routing, focusing on wear-prone areas such as the firewall pass-through, air conditioning housing sheet metal edges, and instrument panel bracket. Repair any damaged wiring and install corrugated conduit for protection.
  • 5
    If the wiring harness is normal, perform a sensor substitution test: install a known-good sensor, clear the fault code, run the air conditioning system for 10 minutes, and observe if the fault code reappears. If the fault persists, check the air conditioning controller (ACU) and LIN line communication (some models use LIN bus communication; measure the waveform).
  • 6
    After completing the repair, perform the air conditioning system self-learning procedure (if applicable). Use a smoke generator to test the air quality sensor response. Confirm the automatic fresh air/recirculation switching function operates normally. Clear the fault code and road test the vehicle to verify.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro DM PM2.5 sensor short circuit after driving through water

✓
The vehicle waded through water about 30 cm deep. The next day, the AC panel showed an air quality detection fault. Diagnosis found DTC B110811. Disassembly revealed the PM2.5 sensor is mounted at the lowest point of the air conditioning intake duct. Water had clearly entered the connector, causing electrolytic corrosion between the pins and a short circuit. Fix: replaced the sensor, cleaned the connector terminals, rerouted the wiring harness (raised the connector position and applied waterproof wrapping), and unblocked the AC drain hole. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Fault after replacing cabin air filter on Qin EV300

✓
After the owner replaced the cabin filter, the dashboard warning light came on. Inspection found the filter was installed incorrectly, keeping the air duct cover from closing fully. The cover clip then crushed and damaged the wiring harness. The sensor's 5V supply wire shorted to the shield ground wire. Repaired the two damaged wires (power and ground), re-wrapped the harness, and adjusted the harness clip position to avoid interference with moving parts. After clearing the fault codes, the air quality function returned to normal.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro EV sensor aging, internal short circuit

✓
80,000 km. Intermittent B110811 fault, occasional automatic AC recirculation failure. Normal when cold; fault frequency increased when hot. Measured sensor signal line-to-ground resistance during fault: 0.3 Ω (normally high impedance). Diagnosed short circuit caused by thermal stability failure of the sensor's internal laser detection circuit. Replaced genuine PM2.5 sensor (part number: HA-8123456-001). Fault completely resolved.
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.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.
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]