AU
B110913

DTC B110913 indicates an open signal circuit for the PM2 — Seal U

Thermal Management System

DTC 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.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Internal open circuit or aging failure of the PM2.5 sensor, interrupting signal output.
  • 2Loose sensor wiring harness connector, backed-out pin, or corroded or oxidized terminal causing poor contact.
  • 3Vibration wear or crushing at the firewall grommet or instrument panel frame broke a wire in the harness.
  • 4Sensor 5V reference voltage circuit or ground circuit fuse blown (e.g., F2-17 air conditioning system fuse)
  • 5Air conditioning controller (AC ECU) internal signal sampling circuit fault; cannot recognize sensor input.
What To Do
  • 1
    Use VDS2000 or a BYD dedicated diagnostic tool to read the complete fault codes and freeze frame data. Confirm the ambient temperature, vehicle speed, and air conditioning status when the fault occurred. After ruling out an intermittent fault, clear the fault codes and perform a road test to verify if the fault returns.
  • 2
    Remove the front passenger glove box or A/C filter. Visually inspect the PM2.5 sensor (usually marked 'Air Quality Sensor') installation status. Verify the wiring harness connector is fully seated. Inspect the terminals for green oxidation or backed-out pins. Clean with electronic contact cleaner if necessary.
  • 3
    Disconnect the sensor connector. Use a multimeter to measure the supply voltage (should be 5V±0.25V) and ground resistance (should be less than 1Ω) on the wiring harness side. If the supply voltage is abnormal, check fuse F2-17 and the supply circuit. If the ground is abnormal, check ground point G301.
  • 4
    Measure the continuity of the signal wire (usually yellow or blue) between the sensor connector and pin T32-15 of the air conditioning controller connector. Normal resistance must be less than 2 Ω. If resistance is infinite, inspect the wiring harness section by section, focusing on wear at the firewall grommet and dashboard frame retaining clips.
  • 5
    If the wiring harness is normal, use an oscilloscope to check the sensor signal output (should be a PWM signal or analog voltage), or directly replace the PM2.5 sensor with a known-good unit for testing. If the fault code clears, the sensor is faulty.
  • 6
    If the fault persists after replacing the sensor, check the A/C controller software version and update to the latest version if necessary. If the software is normal, measure the controller internal sampling resistor to confirm an internal circuit fault and replace the AC ECU.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro EV sensor connector worked loose, causing intermittent fault codes

✓
Started the car after overnight parking. Dash displayed "Air Conditioning System Fault". Scanned: DTC B110913. Inspected and found the PM2.5 sensor connector behind the passenger glovebox wasn't fully locked—it came loose with a light pull. Reconnected the connector and secured the harness with zip ties to relieve strain. Fault cleared. Root cause: Owner recently replaced the cabin air filter and accidentally bumped the sensor connector, leaving it not fully seated.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin EV300 wiring harness chafing caused signal wire open circuit

✓
When driving on rough roads, the AC panel showed abnormal readings. A scan tool retrieved stored DTC B110913. Teardown inspection found that prolonged vibration had damaged the sensor wiring harness insulation where it passes through the firewall metal sleeve. The signal wire's internal copper strands had broken while the outer jacket remained intact, causing an intermittent open circuit. Repaired the harness, added abrasion-resistant sleeving, and rerouted and secured the wiring away from sharp metal edges. Fault fully resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro DM sensor body aging failure

✓
This DTC appeared after 4 years of use. Checked power and ground circuits – both normal. Signal line continuity tested good. Measured infinite resistance at the sensor output terminal (spec: 1.5–2.5 kΩ), indicating the internal laser detection module had aged and failed open-circuit. Replaced with OEM PM2.5 sensor (part number BYDEG-8121400). After replacement, data stream showed normal PM2.5 values. Cleared the DTC and it has not returned.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin EV300 wiring harness chafing caused signal wire open circuit

✓
When driving on rough roads, the A/C panel showed erratic readings. The scan tool read stored fault code B110913. Disassembly inspection found the sensor wiring harness insulation damaged at the firewall metal grommet from prolonged vibration. The signal wire's internal copper strands were broken but the outer sheath remained intact, causing an intermittent open circuit. Repaired the harness, added abrasion-resistant sleeving, and rerouted and secured the harness to avoid contact with sharp metal edges. Fault 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.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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.
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]