AU
B166F-00

DTC B166F-00 indicates the airbag control unit (SRS ECU) detects a communication loss or electrical disconnection with the right side impact sensor — Seal U

Safety System

DTC B166F-00 indicates the airbag control unit (SRS ECU) detects a communication loss or electrical disconnection with the right side impact sensor.

This sensor typically mounts in the right B-pillar or inside the door to monitor side-impact acceleration and serves as the key input device to trigger the right side airbag and curtain airbag.

The ECU sets this fault code if it fails to receive a valid signal from the sensor within the set cycle, or detects an open or short circuit in the wiring.

This fault forces the right side airbag system into fail-safe mode.

The airbags may fail to deploy during a side impact, severely compromising occupant passive safety.

The instrument cluster continuously illuminates the SRS warning light.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Loose connector or poor contact: Right side impact sensor connector not fully locked, or terminal backed out or oxidized, interrupting signal transmission. Commonly occurs after vehicle wading, car washing, or vibration from repeated door opening and closing.
  • 2Wiring harness open or short circuit: The wiring harness connecting the sensor to the SRS ECU shows wear, chafing, or breaks at the door hinge, B-pillar wiring pass-through, or body bend points, or shorts to ground or power.
  • 3Internal fault in the sensor body: An open circuit in the sensor internal circuitry or a damaged communication chip prevents the ECU from recognizing the sensor ID and signal.
  • 4Water damage or corrosion: Vehicle wading or aging seals allow rainwater to seep into the B-pillar, oxidizing and corroding the sensor connector pins, resulting in contact resistance or an open circuit.
  • 5SRS ECU terminal fault: Poor contact at the corresponding pin on the airbag control unit side, or internal driver circuit fault (less common, but requires inspection).
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS or ED400) to read fault codes, confirm B166F-00 is a current fault (Active), record freeze frame data, and check for other SRS fault codes.
  • 2
    Turn the power OFF, disconnect the battery negative terminal, and wait at least 90 seconds for the system to discharge. Inspect the right side impact sensor (usually located inside the right B-pillar trim or inner door panel) for physical damage or impact marks.
  • 3
    Disconnect the sensor connector and inspect the terminals for push-out, deformation, oxidation, or corrosion. Measure the connector latch retaining force. If necessary, clean the terminals with electronic contact cleaner and reconnect the connector.
  • 4
    Disconnect the SRS ECU connector (located under the center console or center tunnel). Use a multimeter to measure sensor wiring harness continuity: measure the circuit resistance between the ECU terminal and the sensor terminal (normal resistance is less than 1 Ω) and check the continuity of the W/L (signal) and W/G (ground) wires.
  • 5
    Measure circuit insulation: Check wiring harness resistance to ground (should be greater than 10MΩ) and check for short circuits to power. Inspect the door hinge and inside the wiring harness sleeve below the B-pillar for wear or damaged insulation.
  • 6
    Perform a swap test: Swap the right side impact sensor with the left side impact sensor (if the models are identical). Power on the vehicle and read the fault code. If the fault code changes to B166E-00 (left side), the sensor is faulty. If the fault code remains B166F-00, the wiring harness or ECU is faulty.
  • 7
    Replace the confirmed faulty part (sensor or wiring harness). During installation, use a torque wrench to tighten the sensor retaining bolts to the specified torque (usually 8-10 N·m). Install the sensor in the correct direction (arrow pointing toward the front of the vehicle).
  • 8
    Reconnect all connectors and the battery. Set the power to ON. Use the diagnostic tool to clear the fault code. Perform the SRS system self-check. Confirm B166F-00 does not reappear and the instrument cluster SRS warning light turns off. Perform 3 ignition cycles to confirm the fault is resolved.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD ATTO 3 / Yuan PLUS right side impact sensor connector loose

✓
The SRS warning light on the instrument panel illuminated. The scan tool retrieved DTC B166F-00. Inspection revealed the right side impact sensor connector was not fully latched, likely because it wasn’t fully seated during a previous B-pillar trim repair. Reconnected the connector and cleared the fault code, which resolved the issue. This type of case shows that connector inspection should be the first step, and the fault can be eliminated without replacing components.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

SRS wiring harness open-circuit repair on BYD Qin sedan

✓
Airbag warning light stayed on. Retrieved DTC B166F-00. Inspection found the wiring harness between the right side impact sensor and SRS ECU had fractured internally at the lower B-pillar grommet due to long-term flexing. Outer sheath appeared intact, but the circuit read infinite resistance. After repairing the harness (soldered, insulated, and waterproofed), circuit resistance returned to normal (<0.5Ω) and the fault cleared.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin EV Sensor Unit Fault: Swap Verification Case

✓
The vehicle logged DTC B166F-00. Initial checks showed normal wiring harness continuity and no connector abnormalities. The technician performed a swap test: after exchanging the right and left side impact sensors, the fault code changed to left sensor not connected (B166E-00), confirming an internal circuit fault in the original right sensor. Replacing the right side impact sensor with a new one (part number must match the vehicle model) completely resolved the fault.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

E1 EV wiring harness chafed at the door hinge

✓
The SRS warning light came on after driving over bumpy roads. The diagnostic tool displayed code B166F-00. Inspection found the right front door wiring harness boot damaged at the hinge, with the internal signal wire worn through from repeated door opening and closing. This type of fault is common in commercial vehicles such as ride-hailing cars due to frequent door use. Replaced the door wiring harness assembly, adjusted the harness routing, and added a protective sleeve to complete the repair.
BYD DTC AI AnalysisFrom Chinese market (translated)

Oxidised and corroded sensor connector on flood-damaged vehicle

✓
After water ingress repairs, the vehicle logged DTC B166F-00 indicating an abnormal right side impact sensor signal. Disassembly revealed water inside the B-pillar sensor connector; the pins had oxidised and blackened, creating contact resistance (measured approximately 15Ω; normal is less than 1Ω). Cleaned the terminals with precision electronics cleaner, applied conductive protective grease, and checked the drain holes were clear. Cleared the fault codes and the system returned to normal.
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]