AU
B165400

DTC B165400 indicates the airbag control unit (SRS ECU) detects a communication interruption with the Left Front Impact Sensor during a self-test or drive cycle — Atto 3

Safety System

DTC B165400 indicates the airbag control unit (SRS ECU) detects a communication interruption with the Left Front Impact Sensor during a self-test or drive cycle.

This sensor typically mounts on the left front longitudinal member (inside the fender or near the headlamp bracket) and detects front collision acceleration signals. "Not connected" indicates a disconnected physical plug, an open circuit in the sensor power/ground wiring, an open CAN/LIN communication line, an internal sensor open circuit, or a poor connection at the ECU connector.

An active fault forces the SRS system into a degraded mode.

This condition may prevent the left front airbag, driver airbag, or seatbelt pretensioner from deploying correctly during a collision, and illuminates the instrument cluster airbag warning light (flashing or solid).

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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1After front-end accident repairs, the left front crash sensor connector is not fully seated, or a broken locking tab causes it to loosen. This commonly occurs after removing and installing the front bumper, headlight, or fender.
  • 2Sensor wiring harness wear causing an open circuit. This mostly occurs in the front side member area. Bottoming out, wading, or long-term vibration damages the harness insulation and breaks the internal copper wires, especially due to an aged protective sleeve where the harness passes through the front side member hole.
  • 3Internal sensor fault, such as a damaged piezoelectric element, internal open circuit, or ID chip failure, preventing valid communication with the SRS ECU.
  • 4Poor contact at the SRS control unit connector or an internal ECU fault prevents the specific channel from detecting the sensor resistance (normally about 2.0-3.0kΩ).
  • 5Accidental cutting or damage to the collision sensor wiring harness during vehicle modification or installation of aftermarket equipment (such as front radar or spotlights), or sensor mounting bracket deformation causing the connector to loosen under tension.
What To Do
  • 1
    Connect the VDS2000 or Launch X431 diagnostic tool, enter the SRS system, and read the complete fault codes to confirm whether B165400 is a current fault (Active) or a history fault (History). After clearing the fault codes, perform a road test or simulated vibration test to observe whether the fault reoccurs. Simultaneously record the Freeze Frame data to check the vehicle speed and ambient temperature when the fault occurred.
  • 2
    Disconnect the battery negative terminal (follow the high-voltage power-down procedure; for hybrid models, ensure the READY light is off). Wait 90 seconds for the capacitors to discharge. Remove the left front fender liner or front bumper. Visually inspect the 2-pin or 3-pin connector of the left front crash sensor (located at the front of the left front longitudinal beam or below the headlamp) for a secure connection. Inspect the locking tab for breakage and the terminals for backing out, corrosion, water ingress, or white oxidation.
  • 3
    Test the sensor wiring harness using a multimeter: disconnect the sensor connector and measure the voltage to ground on the harness side (Expected: 0V; abnormal voltage indicates an ECU or wiring short circuit). Measure the resistance between the sensor power wire and ground (Expected: < 1Ω). Check harness continuity using the multimeter buzzer. Inspect specifically for hidden open circuits inside the harness protective sleeve at the front longitudinal beam pass-through. If equipped with dual sensors, swap the left and right sensors to determine if the fault follows the sensor.
  • 4
    Measure sensor internal resistance: Disconnect the sensor and measure the resistance between its terminals using a multimeter. The normal value is 2.0kΩ±10% (refer to the repair manual for details). Infinite or zero resistance indicates an internal open or short circuit; replace the sensor. When installing a new sensor, use a genuine OEM part and apply the specified torque (typically 8-10N·m). Never use aftermarket or salvaged parts, as these may cause an ID mismatch.
  • 5
    After completing the repair, connect the battery and turn the ignition switch to the ON position. Use the diagnostic tool to perform "SRS System Configuration" or "Sensor ID Registration" (required for some Qin Pro and E2/E3 models). Clear the fault codes and perform an "SRS System Self-check". Finally, perform a vehicle crash simulation test (using a dedicated tester) or a road test to confirm the fault code does not reappear and the airbag warning lamp turns off normally (6 seconds after the self-check).
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro DM airbag warning light stays on after accident repair

✓
A 2019 BYD Qin Pro DM had its front bumper and left headlight replaced at a repair shop after a minor front collision. Afterwards, the airbag warning light on the instrument panel stayed on constantly. The stored DTC was B165400 (current). Inspection found the collision sensor connector on the left front side member was not fully seated and its locking tab had broken. The repair shop technician, unfamiliar with the BYD SRS system, pulled on the wiring harness while fitting the bumper, causing the connector to come loose. Replaced the wiring harness connector (with harness assembly), reconnected the sensor, cleared the fault codes, and performed a VDS system self-test. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD E2 left front sensor communication fault after water ingress

✓
2020 E2 EV. After driving through floodwater during heavy rain, the airbag warning light illuminated. The scanner logged DTCs B165400 and B165500 (right front) simultaneously. Inspection found damage to the wiring harness protective sleeve beneath the left front chassis rail in the front compartment. Water ingress corroded the sensor connector; the oxidized pins produced green copper deposits. Cleaned the connector with WD-40 precision electrical contact cleaner. Wiring harness continuity tested normal, but the sensor internals had short-circuited due to moisture. Replaced the left front impact sensor and waterproofed the harness using heat shrink tubing and waterproof sealant. Fault rectified. Warning: EV wading depth must never exceed half the tyre height.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin EV sensor wiring harness underbody scrape wear causes intermittent fault.

✓
2019 BYD Qin EV. The owner reported the airbag warning light illuminated intermittently, especially on rough roads. DTC B165400 was an intermittent historical fault. We raised the vehicle and inspected the airbag crash sensor wiring harness beneath the left front longitudinal rail. Where the harness passes through the rail opening, an underbody impact had worn through the protective sleeve. Only 2–3 copper strands remained connecting the wires, causing intermittent electrical contact while driving. We cut out the damaged harness section, crimped new waterproof terminals, insulated with double-layer heat shrink tubing, and re-routed the harness to prevent chafing against the rail edge. The fault did not return.
BYD DTC AI AnalysisFrom Chinese market (translated)

E3 front radar installation incorrectly modified collision sensor wiring

✓
2020 E3. After the customer had front parking sensors installed at an external workshop, the airbag warning light stayed on continuously when starting the vehicle. DTC B165400. Inspection found the retrofit shop mistakenly tapped into the left front collision sensor wiring harness, thinking it was the radar power wire. This caused a short circuit in the sensor circuit, and the SRS ECU protectively disabled that channel. Repaired the wiring harness (removed the wire taps, soldered the wires, and sealed with heat-shrink tubing). Replaced the damaged collision sensor (internally shorted). Recoded the SRS ECU to unlock the channel (the ECU had locked it after detecting the short). Fault resolved. Advised the customer to have accessories fitted at an authorised dealer.
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]