AU
B110D

DTC B110D indicates a failure of the Photoelectric Receiving Module in the in-cabin PM2 — Seal U

Thermal Management System

DTC B110D indicates a failure of the Photoelectric Receiving Module in the in-cabin PM2.5 detection system.

In the BYD Song MAX Green Purification System, the PM2.5 sensor operates on the laser scattering principle: a laser diode emits a light beam of a specific wavelength through an air sample, and airborne particles scatter the light.

The Photoelectric Receiving Module (usually containing a photodiode or photomultiplier tube) captures the scattered light signal and converts it into an electrical signal.

When this module fails, the system cannot accurately detect the in-cabin PM2.5 concentration.

This failure disables the automatic air purification function, disrupts the A/C automatic fresh air/recirculation switching function, and may trigger an air quality detection fault on the instrument cluster.

Although this fault does not directly affect vehicle power or core thermal management functions, it disables the intelligent A/C purification system and impairs in-cabin air quality management during severe smog conditions.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Dust or contamination on the photoelectric sensor optical window: After prolonged use, dust, oil vapor, or condensation accumulates on the sensor lens surface. This attenuates or abnormally scatters the received optical signal, triggering a module failure warning.
  • 2Aging or damaged photoelectric receiver module circuit: Photodiode, operational amplifier, or ADC chip degrades or short-circuits due to long-term operation in high-temperature and high-humidity environments.
  • 3Poor contact or corrosion at the wiring harness connector: Vibration and temperature cycling loosen or oxidize the terminals of the PM2.5 sensor plug near the air conditioning duct, interrupting signal transmission.
  • 4BCM (Body Control Module) or air conditioning controller communication fault: A short circuit or open circuit in the LIN/CAN communication line between the receiving module and the main control unit, or an internal software error in the control module, prevents sensor signal recognition.
  • 5Electromagnetic interference from non-OEM aftermarket equipment: Improper power connections or incorrect wire routing of unauthorized aftermarket devices, such as dash cams and air purifiers, generates electromagnetic interference that reduces photoelectric signal acquisition accuracy.
What To Do
  • 1
    Use a dedicated BYD diagnostic tool (VDS or ED400) to read all fault codes. Confirm B110D is a current fault, not a history fault. Check for accompanying communication fault codes (codes starting with U).
  • 2
    Remove the PM2.5 sensor assembly located inside the air conditioning duct or instrument panel (on the Song MAX, this is usually at the air inlet duct inside the center console). Inspect the photoelectric receiving window for obvious dust contamination or physical damage. Clean the optical window using anhydrous ethanol and an anti-static cloth.
  • 3
    Check the sensor wiring harness connector (3-4 pin plug) terminals for oxidation or backed-out pins. Measure the supply voltage (12V or 5V, depending on configuration). Check the LIN line or signal line voltage (normally approx. 8-11V). Confirm a good ground connection.
  • 4
    Use an oscilloscope to check the photoelectric receiver module output signal waveform. It normally generates a pulse signal when particulate matter is present. If the signal amplitude is too low or there is no output, replace the PM2.5 sensor assembly (part number usually begins with K9C or SA2).
  • 5
    Check the vehicle for non-genuine aftermarket equipment (especially recently installed dash cams or head-up displays). Check if these devices draw power from BCM-related fuses. If necessary, correct the wiring routing or remove the devices for testing.
  • 6
    After replacing the sensor, perform the 'Green Clean System Calibration' or 'Air Quality Sensor Adaptation' procedure (access A/C system special functions via the diagnostic tool). Clear the fault codes and perform a road test. Confirm the PM2.5 display value updates with environmental changes in A/C automatic mode.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

2018 Song MAX: Aftermarket equipment causing communication interference with the photoelectric module

✓
The instrument cluster intermittently displayed 'Air Quality System Fault'. Retrieved DTC B110D. Inspection found the customer had recently installed a dashcam, tapping power directly from the fuse box on the left side of the dashboard and sharing the circuit with the PM2.5 sensor. Poor power filtering of the dashcam generated high-frequency interference, causing abnormal signal transmission in the photoelectric receiver module. Relocated the dashcam power supply to the cigarette lighter socket or a separate fuse, and fitted a ferrite core filter. Fault resolved.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

2019 Song MAX: PM2.5 sensor optical window contamination failure

✓
After two years of use, the automatic air purification function failed. Retrieved DTC B110D. Removed the PM2.5 sensor inside the centre console and found an oily dust mixture covering the photoelectric receiver module lens (presumably caused by long-term smoking in the vehicle and use of a poor-quality cabin filter). Cleaning the optical window with anhydrous ethanol was ineffective, as the stains had penetrated internally. Replaced the PM2.5 sensor assembly with a new one (part number: K9C-8121210), performed system calibration, and resolved the fault.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

2017 Song MAX: Poor wiring harness contact causing intermittent B110D fault

✓
When driving on rough roads, the dashboard occasionally showed an air quality fault. It was normal when stationary. The scan tool read intermittent fault code B110D. Checked the PM2.5 sensor connector behind the glove box and found slightly oxidised and loose terminals. Cleaned the terminals with electronic cleaner and re-crimped them using a terminal removal tool. Wrapped the connector with electrical tape to prevent loosening. Also checked the LIN line resistance between the BCM and sensor (normal: <1 Ω). The fault did not recur after the repair.
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]