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AU
B110F

DTC B110F indicates an actuator circuit failure in the solenoid valve (switching valve) inside the PM2 — Seal U

Thermal Management System

DTC B110F indicates an actuator circuit failure in the solenoid valve (switching valve) inside the PM2.5 air quality detection module.

This solenoid valve controls the physical switching of the sampling air passage to select the channel for in-cabin or outside air sampling.

The air conditioning controller (ACU) triggers this code if it issues a switching command but fails to detect the solenoid valve current feedback or position confirmation signal (such as Hall sensor feedback), or if it detects a coil short or open circuit.

This failure prevents the system from accurately comparing the PM2.5 concentration difference between the cabin and outside air, disables Auto Clean mode, and may force the air conditioning system into a protective recirculation mode.

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Cases Logged
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Song MAX DM solenoid valve coil open circuit caused air conditioning auto mode failure

✓
When the vehicle arrived at the workshop, the dashboard displayed 'Air Quality System Fault'. The air conditioning had been stuck in recirculation mode for a long time and could not switch automatically. I measured the resistance between pins 3-4 of the PM2.5 module solenoid valve with a multimeter; the reading showed infinite resistance (normal: 45Ω). Disassembly revealed oxidised dry solder joints inside the coil. I replaced the PM2.5 sensor assembly (part number: HA-8121400). The fault was resolved, and Auto mode returned to normal, allowing automatic switching to fresh air mode for purification.
BYD DTC AI AnalysisFrom Chinese market (translated)

Song MAX petrol: valve spool sticking causes intermittent DTCs

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The owner reported intermittent air conditioning odor and a dashboard warning. The scan tool showed B110F as an intermittent fault. During disassembly, I found significant dust and cotton lint accumulated on the solenoid valve spool guide rail (the owner frequently drives through textile industrial areas), causing excessive resistance in armature movement. The controller detected an abnormal drive current waveform with peak current continuously exceeding 800mA. After cleaning the valve spool with electronic cleaner and applying silicone-based grease, the current waveform returned to normal and the fault code cleared. I advised the owner to replace the cabin air filter regularly (CN95 grade).
BYD DTC AI AnalysisFrom Chinese market (translated)

Dashboard wiring harness chafing caused intermittent power to the solenoid.

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After driving over rough roads, the warning light came on. Checked the PM2.5 module solenoid valve supply voltage, which was only 3.2V and unstable. Traced the wiring harness along the dashboard frame and found the body harness rubbing against a metal bracket. The insulation had worn through, causing partial fracture of the copper strands and a poor connection with about 15Ω resistance. Repaired the harness by soldering and sealing with heat shrink tubing, then rerouted and secured it, adding corrugated tubing and extra cable tie mounting points. This completely resolved the fault.
BYD DTC AI AnalysisFrom Chinese market (translated)

Air conditioning controller driver chip failure caused multiple system faults

✓
Both B110F (PM2.5 solenoid valve) and B2A2F (recirculation motor) DTCs were present. The solenoid valve resistance and voltage measured normal individually, but the active test produced no current output. Removing and disassembling the climate control module revealed the solenoid valve driver chip (L99MC6 or similar H-bridge type) had overheated and burned, with scorch marks on the surface. Replaced the climate control module assembly (online immobiliser matching and configuration coding required). This resolved the fault. Root cause: a previously installed non-genuine dashcam; when splicing into the power supply, the installer accidentally touched the climate control wiring, causing a voltage surge.
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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.