AU
B110E09

This DTC indicates a functional failure of the temperature and humidity sensing module in the PM2 — Seal U

Thermal Management System

This DTC indicates a functional failure of the temperature and humidity sensing module in the PM2.5 air quality rapid detection system.

This module integrates into the PM2.5 detector and monitors ambient air temperature and relative humidity in real time.

The system uses these readings to compensate and correct the light-scattering measurement data from the laser particulate sensor, as temperature and humidity changes significantly affect PM2.5 detection accuracy.

An abnormal analog signal or digital communication interruption causes this fault.

This prevents the air conditioning controller from obtaining accurate ambient temperature and humidity parameters, disabling the automatic air purification, negative ion generator linkage, and air quality display functions.

Although the system classifies this as a "severe" fault, it only affects comfort features and does not impact the powertrain or driving safety.

The vehicle can travel a short distance to a repair facility.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Physical damage to the temperature and humidity sensor element: internal NTC thermistor open/short circuit or humidity-sensitive capacitor failure, causing the output signal to fall outside the valid 0.5-4.5V range.
  • 2Poor wiring harness connector contact: A loose sensor connector, backed-out pins, or oxidized terminals in the center of the dashboard or on the air conditioning intake housing cause intermittent signal interruption.
  • 3Power supply circuit fault: Damaged sensor 5V reference voltage module or excessive ground circuit resistance (>1Ω), causing unstable sensor operating voltage.
  • 4Condensation intrusion into the module: The PM2.5 detector mounts near the air conditioning evaporator housing. Prolonged exposure to low temperatures generates condensation, corroding the temperature and humidity module PCB.
  • 5Sensor calibration data lost: Failure to perform the temperature and humidity sensor zero-point calibration after replacing the air conditioning controller or PM2.5 module causes the ECU to judge the signal as invalid.
What To Do
  • 1
    Use the VDS2000/VDS3000 diagnostic tool to read all fault codes. Check for B110E09 and accompanying B110A02 (CAN fault) or U-series communication faults. Record the ambient temperature value from the freeze frame data.
  • 2
    Remove the center dashboard trim and locate the PM2.5 sensor (usually behind the air conditioning control panel or inside the center air vent). Check the wiring harness connector for looseness. Measure the voltage between plug pin 1 (power) and pin 3 (ground). Standard value: 5V±0.25V.
  • 3
    Disconnect the connector and measure the resistance to ground at the temperature and humidity sensor signal pin (2#): temperature sensor resistance should be 2-3kΩ at 25℃ (NTC characteristic), and humidity sensor resistance should be 200Ω-20kΩ, varying with humidity. If the resistance is infinite or close to 0Ω, the sensor is damaged.
  • 4
    If the power supply and sensor are normal, check wiring harness continuity: the signal wire resistance between the PM2.5 sensor connector and the air conditioning controller (or BMS/thermal management controller, depending on vehicle configuration) must be <1 Ω, and the insulation resistance to body ground must be >10 MΩ.
  • 5
    Replace the PM2.5 sensor assembly (the temperature and humidity module is generally not supplied as a separate spare part). Calibrate the sensor after installation: access 'Air Conditioning System - Special Functions - PM2.5 Sensor Calibration' using the diagnostic tool. Follow the prompts to complete the temperature and humidity zero-point calibration, clear the fault code, and verify with a road test.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin Pro DM instrument cluster intermittently displays 'Air Quality Detection Fault'

✓
After parking overnight, started the vehicle. The dashboard indicated an air quality system fault, and the air conditioning auto mode could not activate the purification function. Retrieved current fault code B110E09 using a diagnostic tool. Inspection found the PM2.5 sensor above the centre console; its wiring harness plug retaining clip had broken, causing the connector to work loose. When the vehicle vibrated during driving, the signal would cut out. Resecured the plug and reinforced it with cable ties. Cleared the fault codes and observed the temperature and humidity data displayed normally. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro EV PM2.5 function inoperative after air conditioning repair

✓
After replacing the evaporator assembly at the dealership, I noticed the centre screen no longer showed the outside PM2.5 value. Retrieved DTC B110E09. Inspection found that during the dashboard removal, a tool had touched the temperature and humidity sensor probe on the PM2.5 detector, physically damaging the internal humidity-sensitive element. Measured the sensor signal line voltage: constant 4.9 V (normally it should fluctuate between 1–4 V with temperature and humidity changes). Replaced the PM2.5 detector assembly, then performed the 'Air Quality Sensor Learning' function using the diagnostic tool. Live data showed 25 °C and 60% humidity; function returned to normal.
BYD DTC AI AnalysisFrom Chinese market (translated)

Prolonged exposure to high humidity caused sensor corrosion

✓
Vehicle used in a coastal city. After 2 years, DTC B110E09 appeared. Removed and inspected the PM2.5 sensor and found obvious salt spray corrosion on the internal circuit board, with oxidised solder joints on the temperature and humidity sensor. The cause was prolonged high-load operation of the air conditioning system combined with coastal humidity, resulting in moisture ingress to the sensor module. After cleaning the corrosion from the circuit board, the fault cleared temporarily, but returned after one week. Replaced the PM2.5 sensor and applied conductive anti-corrosion grease to the wiring harness connector, permanently fixing the fault.
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]