AU
B110D09

DTC B110D09 indicates a failure of the internal photoelectric receiving module in the PM2 — Seal U

Thermal Management System

DTC B110D09 indicates a failure of the internal photoelectric receiving module in the PM2.5 rapid detector (laser particulate sensor).

The sensor operates on the laser scattering principle: a laser diode emits a beam to illuminate an air sample.

Suspended particulate matter produces scattered light.

The photoelectric receiving module (typically a high-sensitivity photodiode or photomultiplier tube) captures this light and converts it into an electrical signal.

The signal processing circuit then calculates the PM2.5 concentration.

DTC B110D09 specifically refers to a fault in the module receiving the scattered light.

Possible causes include photoelectric component aging or burnout, a signal amplification circuit fault, A/D conversion module damage, or an internal open circuit.

This fault prevents the Green Air Purification System from obtaining accurate air quality data, disabling the automatic air purification mode and the A/C automatic fresh air/recirculation switching function.

Although this fault typically does not affect the powertrain or driving safety, it disables the thermal management system's environmental adaptive control strategy.

The system classifies this fault as severe because abnormal communication between the sensor and the A/C control module can trigger cascading faults.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Aged or burned-out photodiode inside the photoelectric receiving module: Optical fatigue from long-term laser exposure or electrostatic discharge causes the photoelectric component to degrade or fail completely, preventing it from generating a valid photocurrent signal.
  • 2Sensor circuit board fault: Overvoltage (vehicle voltage fluctuations), thermal stress, or manufacturing defects damage the signal amplification circuit, filter circuit, or microprocessor chip, preventing photoelectric signal processing.
  • 3Wiring harness connector issue: Connectors near the centre console or air-conditioning duct loosen due to vehicle vibration, pins oxidise, moisture enters (air-conditioning condensate seepage), or contact resistance becomes excessive, interrupting signal transmission.
  • 4Severe optical path contamination: Excessive dust or fibers block the sensor air inlet or optical chamber, preventing the photoelectric receiving module from receiving scattered light signals for an extended period and triggering a fault, or excessive laser reflection overloads and damages the receiver.
  • 5Abnormal supply voltage: A short circuit or short to ground in the sensor power supply circuit causes excessively high or low input voltage, exceeding the operating voltage range of the photoelectric receiver module (typically 5V ± 0.5V) and damaging the internal circuit.
What To Do
  • 1
    Use the BYD VDS2000/VDS2100 diagnostic tool to access the air conditioning/thermal management system. Read and record the complete fault codes and freeze frame data. Confirm only B110D09 or related communication fault codes are present. Check if the PM2.5 real-time data stream displays a fixed, zero, or invalid value.
  • 2
    Locate the PM2.5 sensor (usually inside the center console, behind the glove box, or at the A/C evaporator air inlet). Inspect the sensor exterior for physical damage, cracks, or signs of water ingress. Check the mounting bracket for looseness.
  • 3
    Disconnect the sensor electrical connector. Use a multimeter to check the harness-side supply voltage (should be 5 V or 12 V, depending on vehicle configuration), ground wire continuity (resistance < 1 Ω), and signal wire-to-ground resistance. Confirm the wiring has no short or open circuits.
  • 4
    Check the cleanliness of the sensor optical window. Gently wipe the lens surface with anhydrous ethanol and an anti-static cloth to remove dust and oil. (Note: Clean the exterior only; do not dismantle the sealed sensor housing.) Check the air intake passage for blockages.
  • 5
    Reconnect the sensor, clear the fault code, start the vehicle, and turn on the air conditioning. Observe the data stream to verify the PM2.5 value updates dynamically with environmental changes. If the fault code reappears immediately or the value remains unchanged, the sensor's internal photoelectric receiving module is damaged. Replace the PM2.5 sensor assembly.
  • 6
    Install the new sensor (note orientation requirements on some models) and seat the sealing ring correctly to prevent air leaks. Use the diagnostic tool to perform the 'Air Quality Sensor Initialisation' or 'Green Clean System Self-learning' function (path: Special Functions → Air Conditioning System → Sensor Calibration) to complete the baseline calibration of the new sensor.
  • 7
    Verify the repair: Check the instrument panel PM2.5 display for normal operation (a reading typically appears within 30 seconds of startup), test the automatic purification function (light a cigarette near the sensor to verify automatic switching to recirculation mode and purifier activation), and confirm the fault code does not return.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Atto 3 PM2.5 sensor photoelectric receiver module damaged

✓
Instrument cluster displayed an air quality detection malfunction, and the air purification function failed in automatic AC mode. Scanned the AC system with a diagnostic tool and retrieved DTC B110D09 (PM2.5 detector photoelectric receiver module failure). Checked PM2.5 sensor wiring: connections normal, supply voltage 5V (within spec), no short circuit on signal line. Determined internal photoelectric receiver tube aged and failed from long-term use. Replaced PM2.5 air quality sensor assembly, cleared DTCs, and performed sensor initialization. System returned to normal; PM2.5 readings update correctly with ambient changes.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro EV Green Net system intermittent fault (B110D09)

✓
Owner reported cabin air quality display intermittently disappearing and the Green Air system working inconsistently, sometimes recovering after an ignition cycle. Scan tool retrieved intermittent DTC B110D09. Found the PM2.5 sensor behind the glovebox; its connector was not fully seated, causing intermittent contact when the vehicle vibrated. Reseated the connector and secured it with electrical tape. Sensor optical window also had slight dust contamination; cleaned it and the fault resolved. Live data now shows stable readings.
BYD DTC AI AnalysisFrom Chinese market (translated)

Song Pro DM-i optical receiver module failure due to optical path contamination

✓
After long-term use in a dusty environment (near construction sites), the instrument cluster reported an air quality system fault. Read DTC B110D09. Disassembly revealed heavy dust accumulation inside the PM2.5 sensor optical cavity. Dust on the photoelectric receiver surface prevented light signal reception. Since dust had entered the internal optical components, cleaning only the exterior could not restore function. Replaced the PM2.5 sensor assembly and added filter cotton at the air intake to prevent future contamination. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Han EV dual-zone air quality detection failure - passenger side

✓
The Han EV has a dual-zone PM2.5 monitoring system. The owner noticed the passenger side air quality display constantly showed '--' or a fixed value, while the driver's side worked normally. The scan tool read DTC B110D09, pointing to the passenger side PM2.5 sensor. Power supply and ground to the sensor were normal, but the signal output voltage was 0V (normal analog signal: 0.5-4.5V). This indicated an open circuit in the passenger side sensor's internal photoelectric receiver module. After replacing the sensor, we performed a dual-zone sensor calibration using the scan tool. Both sides now display correctly.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin EV300: Chafed PM2.5 sensor wiring loom caused photoelectric receiver module failure

✓
The vehicle intermittently displayed an air quality system fault warning, with intermittent DTC B110D09. Inspection found the sensor wiring harness insulation had worn through at the dashboard frame mounting point due to long-term friction, leaving the copper wires partially exposed. When the vehicle hit bumps, the exposed wires shorted to the metal frame, causing the photoelectric receiver module supply voltage to drop momentarily and trigger the fault. We repaired the damaged harness (re-insulated and wrapped), rerouted the harness to avoid contact with sharp edges, and replaced the PM2.5 sensor, as voltage fluctuations may have damaged it. The fault was completely resolved.
Other Seal U 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. Sources: [1]