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 — Atto 3

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 — Atto 3
  • 1Sensor wiring harness connector loose, detached, or poor contact: Long-term vehicle vibration, water ingress, or incomplete seating during previous repairs causes a gap or oxidation between the plug and socket.
  • 2Wiring harness open circuit: Crushing or cutting the wiring harness during accident repairs, or long-term wear and aging breaking the wire, results in an open signal circuit.
  • 3Sensor mounting failure: A broken sensor mounting bracket or retaining clip loosens the sensor, straining the wiring harness connector and resulting in poor contact.
  • 4Internal fault in the sensor body: Open internal circuit (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 power mode to OFF, disconnect the 12V battery negative terminal and wait 3-5 minutes (to fully discharge the SRS capacitor), then hang a high-voltage/airbag repair warning sign.
  • 2
    Visual inspection: Remove the right front fender liner or bumper. Inspect the right front crash sensor for visible damage. Check the wiring harness for obvious damage, crushing, or abrasion. Verify the connector is fully inserted.
  • 3
    Connector inspection: Disconnect the sensor connector. Check the terminals for oxidation, recession, or deformation. Measure the engagement tightness between the terminals and the socket. If necessary, clean the terminals 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 plug and the corresponding ECU terminal (normal: less than 1 Ω), and check for shorts to ground or power.
  • 5
    Sensor test: Measure the sensor resistance (refer to the workshop manual, usually several hundred to several thousand ohms). If the resistance is infinite, replace the sensor. Alternatively, perform a substitution test by installing a known-good sensor.
  • 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 and avoid tension on the harness.
  • 7
    System reset and verification: Connect the battery, turn the ignition switch to the ON position, use the diagnostic tool to clear the fault code, perform an SRS system self-diagnosis, confirm B165D no longer appears, and read the data stream to confirm the right front crash sensor status is 'normal'.
  • 8
    Road test verification: Perform a road test, especially over bumpy roads, to confirm the SRS warning light no longer illuminates and full system functionality is restored.
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 Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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]