AU
B165D00

DTC B165D00 indicates the airbag control unit (SRS ECU) detects a communication interruption or physical connection loss with the Right Front Frontal Impact Sensor — Seal U

Safety System

DTC B165D00 indicates the airbag control unit (SRS ECU) detects a communication interruption or physical connection loss with the Right Front Frontal Impact Sensor.

This sensor typically mounts inside the right front bumper reinforcement beam or at the front of the right fender to monitor collision acceleration at the right front of the vehicle.

The SRS ECU sets this fault code if it fails to receive a valid signal from the sensor within a predefined cycle, or if it detects an open circuit or abnormal resistance in the sensor circuit.

The airbag system then enters fail-safe mode, which may prevent the right front airbag, side airbag, or seat belt pretensioner from deploying normally during a collision.

The instrument cluster airbag warning light remains illuminated, and some models may sound a warning buzzer.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Sensor wiring harness connector loose, disconnected, or making poor contact: Commonly caused by an unseated connector or broken retaining clip following front bumper removal and installation, accident repairs, or wading.
  • 2Wiring harness open or short circuit: Front-end collision stretching and breaking the harness, long-term friction against the fender or bumper reinforcement damaging the harness, or rodent bites causing the signal wire to short to ground.
  • 3Crash sensor internal fault: Internal accelerometer damage, electronic component aging, or seal failure causes an internal short circuit, preventing the sensor from returning the correct resistance value (normally 2-3kΩ) to the SRS ECU.
  • 4Mounting bracket or ground fault: Loose sensor retaining bolts cause insecure mounting, or an oxidized or loose sensor ground point causes a poor circuit, affecting signal transmission.
  • 5SRS ECU communication port fault: Damaged internal control unit pin for right front sensor communication, or software logic error (less common; confirm after ruling out wiring faults).
What To Do
  • 1
    Safety preparation: Set the vehicle to OFF, disconnect the low-voltage battery negative terminal, and wait at least 90 seconds to fully discharge the airbag system capacitor and prevent accidental airbag deployment during repair.
  • 2
    Inspection procedure: Remove the right front bumper cover or right front fender liner, locate the right front impact sensor (usually marked 'Front Impact Sensor' or with a part number), and visually check that the connector is fully seated, the locking tab is intact, and the wiring harness has no visible damage.
  • 3
    Voltage measurement: Reconnect the battery. Turn the ignition switch to the ON position (do not start). Use a multimeter to measure the sensor connector terminals for 12V battery voltage (B+), a good ground (GND), and signal voltage (typically a 2.5V reference voltage). If power or ground is missing, check wiring harness continuity.
  • 4
    Circuit continuity test: Disconnect the SRS ECU connector (located under the center console or center tunnel). Use a multimeter to measure the harness resistance between the ECU and the sensor; resistance must be less than 1Ω. Measure the insulation resistance of each wire to ground and to power; resistance must be greater than 10MΩ to rule out a short circuit.
  • 5
    Sensor body test: Turn off the ignition, disconnect the sensor connector, and measure the resistance between the two sensor terminals. The resistance must be 2-3 kΩ (refer to the vehicle repair manual for specific values). Replace the sensor if the resistance is 0, infinite, or deviates by more than ±10%.
  • 6
    Replacement and reinstallation: If the sensor is faulty, replace it with a genuine part (some models require VIN matching). Tighten to the standard torque (usually 8-10 N·m). Point the sensor arrow directly toward the front of the vehicle. Fully seat the connector and secure the wiring harness to prevent interference.
  • 7
    System calibration: Connect the dedicated diagnostic tool (VDS or Launch/Autel equipment supporting the BYD SRS system), clear the fault code, execute the 'SRS System Configuration' or 'Crash Sensor Calibration' procedure, perform an ignition cycle test, and confirm B165D00 does not return and the airbag warning light turns off.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

New vehicle PDI case: Transport plug not connected

✓
Symptoms: During pre-delivery PDI inspection of a 2019 BYD Qin Pro DM, the airbag warning light stayed on constantly. The diagnostic tool read fault code B165D00. Diagnosis: Checked the impact sensor on the inner side of the right front bumper. Found the sensor connector completely unplugged, just loosely attached (during transport). Measured wiring harness voltages: 12V supply, ground, and 2.4V signal — all normal. Measured sensor resistance: 2.8kΩ, normal. Fix: Reconnected the connector properly and confirmed the locking clip fully engaged. Cleared the fault code with the diagnostic tool and ran three ignition cycle tests. The warning light went out and the fault code did not return.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Intermittent connection due to pinched wiring harness after accident repair

✓
Symptoms: 2018 BYD Qin Pro petrol variant. Airbag warning light illuminated after minor front collision repairs, DTC B165D00. Diagnosis: Right front sensor connector visually OK, but signal wire voltage measured only 0.8 V (low). Traced the harness and found the wiring pinched between the bumper reinforcement and fender when the front bumper was reinstalled, causing partial copper wire breakage and high resistance. Solution: Repaired damaged harness (cut out damaged section, re-soldered wires, sealed with heat-shrink tubing). Rerouted wiring away from pinch points and secured with cable ties. Cleaned sensor connector terminals, applied conductive grease. Cleared fault codes, road test confirmed normal.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Connector oxidation and corrosion after wading

✓
Symptoms: 2020 BYD E3 airbag warning light illuminated after driving through water. Diagnostics showed right front impact sensor disconnected. Diagnosis: Removed the right front fender liner and found visible water stains and green corrosion inside the sensor connector. Pin oxidation caused excessive contact resistance (measured 15 Ω, normal <1 Ω). Sensor body resistance and wiring harness continuity were normal. Repair: Cleaned the plug and socket terminals thoroughly with electronic contact cleaner, applied dielectric grease for waterproofing, replaced the waterproof seal, reconnected the connector, and cleared the fault codes. Fault resolved. Recommend inspecting the front bumper seal to prevent recurrence.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Internally damaged sensor body replacement case

✓
Symptoms: 2019 BYD E2, no accident history. Airbag warning light illuminates intermittently, especially during cold starts. DTC B165D00 appears intermittently. Diagnosis: Inspected wiring harness connections – normal. Measured sensor resistance cold at 5.2kΩ (exceeds normal 2–3kΩ range). After warming up, thermal expansion and contraction inside the sensor changed resistance, sometimes restoring normal communication. Tapped the sensor housing lightly; resistance fluctuated noticeably. Diagnosed as faulty internal accelerometer or circuit board solder joint. Repair: Replaced the right front impact sensor assembly (part number matched to VIN). Oriented the arrow parallel to the vehicle's longitudinal axis during installation. Torqued to 9 N·m. Performed system configuration with diagnostic tool; fault cleared completely.
Original source ↗
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]