AU
B165D

DTC B165D indicates the airbag control unit (ACU/SRS ECU) detects an open circuit in the right front impact sensor (RFIS) communication circuit — Seal U

Safety System

DTC B165D indicates the airbag control unit (ACU/SRS ECU) detects an open circuit in the right front impact sensor (RFIS) communication circuit.

The ECU fails to receive a valid signal from the sensor within the specified monitoring period or detects infinite circuit resistance.

Typically mounted on the right front side member (behind the headlamp or inside the fender), the sensor detects collision acceleration at the right front of the vehicle.

This fault forces the airbag system into degraded mode.

In a frontal collision, the ACU may fail to accurately determine impact severity.

This failure delays or prevents the deployment of passive safety devices, such as airbags and seat belt pretensioners, severely increasing occupant injury risk.

The vehicle remains drivable, but safety protection functions are compromised.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Sensor wiring harness connector loose, disconnected, or making poor contact: Long-term vehicle vibration, wading, or incomplete insertion during previous repairs creates a gap or oxidation between the plug and socket.
  • 2Wiring harness open circuit: Crushing or cutting the wiring harness during accident repairs, or wire breakage from long-term wear and aging, causes an open signal circuit.
  • 3Sensor mounting failure: A broken sensor mounting bracket or retaining clip causes the sensor to loosen, straining the wiring harness connector and resulting in poor contact.
  • 4Internal sensor fault: Open circuit in the internal sensor circuitry (such as a detached solder joint or damaged component) preventing communication with the ECU.
  • 5ECU pin issue: SRS ECU connector terminals backed out, oxidized, or deformed, causing poor contact with the wiring harness.
What To Do
  • 1
    Safety preparation: Set the power mode to OFF, disconnect the 12V battery negative terminal and wait 3-5 minutes (ensure the SRS capacitor discharges fully), and hang a high-voltage/airbag repair warning sign.
  • 2
    Visual inspection: Remove the right front fender liner or bumper. Check the right front crash sensor for visible damage. Inspect the wiring harness for obvious damage, crushing, or wear marks. Verify the connector is fully inserted.
  • 3
    Connector inspection: Disconnect the sensor connector and inspect the terminals for oxidation, recession, or deformation. Measure the engagement tightness between the terminals and the socket. If necessary, clean with electrical contact cleaner and apply conductive grease.
  • 4
    Circuit continuity test: Disconnect the SRS ECU connector (observe anti-static precautions). Use a multimeter to measure wiring harness continuity between the sensor connector and the corresponding ECU terminal (normal: less than 1Ω). Check for shorts to ground or power.
  • 5
    Sensor body test: Measure the sensor body resistance (refer to the workshop manual, usually several hundred to several thousand ohms). If the resistance is infinite, replace the sensor. Alternatively, use the substitution method: install a known-good sensor and test.
  • 6
    Reconnect and secure: Fully insert the connector until it clicks. Repair or replace damaged wiring harness retaining clips. Use cable ties to secure the wiring harness to the body. Prevent contact with sharp edges or harness tension.
  • 7
    System reset and verification: Connect the battery, turn the ignition switch to the ON position, and use the diagnostic tool to clear the fault code. Perform an SRS system self-diagnosis to confirm B165D does not return. Read the data stream to confirm the right front crash sensor status is 'Normal'.
  • 8
    Road test verification: Perform a road test, especially on rough roads, to confirm the SRS warning light remains off and the system regains full functionality.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Loose connector on the right front impact sensor caused the SRS warning light to stay on constantly in a BYD S6

✓
After driving over a rough road, the airbag warning light came on. I pulled DTC B165D-00 (Right Front Impact Sensor Not Connected) with a scan tool. I found the impact sensor connector on the right front frame rail wasn’t fully seated and the lock wasn’t engaged. Road vibrations had worked it loose. I reseated the connector firmly, locked the retaining clip, and secured the harness with cable ties to prevent it from loosening again. Cleared the fault code, the SRS light went out, and the problem was fixed.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Open circuit in wiring harness after accident repair caused communication loss.

✓
The vehicle had minor damage on the right front. After an independent repair shop replaced the bumper and right front wing, the airbag warning light stayed on at start-up. The technician read fault code B165D-00. Inspection found that during the repair, the impact sensor harness on the right front side member was accidentally pinched, breaking the insulation and snapping the internal wires. This cut off communication between the sensor and ECU. The technician re-soldered the break point, insulated and waterproofed the joint with heat shrink tubing, and fixed the harness routing. After clearing the fault code, the system returned to normal.
BYD DTC AI AnalysisFrom Chinese market (translated)

Water ingress oxidized the sensor connector, causing poor contact.

✓
After driving through floodwater during heavy rain, the airbag warning light illuminated. The scanner displayed DTC B165D-00 (Right Front Impact Sensor Not Connected). Inspection revealed significant water staining and oxidation corrosion inside the right front impact sensor connector at the right front side member, causing excessive contact resistance that made the system incorrectly detect the sensor as disconnected. Thoroughly cleaned the connector terminals with electronic cleaner to remove the oxide layer, applied a suitable amount of conductive paste to prevent further oxidation, reconnected the plug, cleared the fault codes, and resolved the issue.
BYD DTC AI AnalysisFrom Chinese market (translated)

Right front impact sensor internal circuit open.

✓
No accident history, but the SRS warning light stays on. Retrieved DTC B165D. Checked wiring harness continuity (resistance less than 1 Ω) – normal. Connectors are clean and secure, power and ground both normal. Diagnosed an internal sensor fault. Replaced the right front impact sensor assembly, cleared the DTCs, and performed a system self-test. The warning light went out, and data stream shows sensor communication 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]