AU
B166800

DTC B166800 indicates a functional fault in the Left Side Impact Sensor within the Supplemental Restraint System (SRS) — Atto 3

Safety System

DTC B166800 indicates a functional fault in the Left Side Impact Sensor within the Supplemental Restraint System (SRS).

This sensor typically mounts inside the left B-pillar trim panel or near the left side sill beam.

It contains a built-in accelerometer to detect side-impact acceleration on the left side of the vehicle.

When the sensor detects acceleration exceeding a specific threshold, it sends a crash signal to the SRS ECU, which then determines whether to deploy the left side airbag and side curtain airbag.

This DTC triggers when the SRS ECU continuously fails to receive a valid signal from the sensor (due to communication loss, abnormal signal voltage, or sensor unresponsiveness), disabling the left-side impact protection function.

In this fault state, the side airbag and side curtain airbag may fail to deploy during a side collision, severely endangering occupant safety.

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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1Loose left side impact sensor wiring harness connector, water ingress, or terminal corrosion (common at the B-pillar due to long-term wiring harness bending from frequent door operation)
  • 2Internal failure of the accelerometer element in the sensor body or signal processing circuit fault (due to aging, vibration, or electromagnetic interference)
  • 3Sensor power supply circuit (usually 5V reference voltage) short to ground, short to power, or open circuit, or signal circuit (LIN or CAN communication line) short or open circuit.
  • 4Loose, deformed, or detached sensor mounting bracket causing sensor misalignment or poor internal component contact.
  • 5SRS ECU internal interface circuit fault; unable to correctly interpret the left side crash sensor signal.
What To Do
  • 1
    Use the BYD VDS diagnostic tool to read complete fault codes and freeze frame data. Verify environmental parameters at the time of the fault, including vehicle speed and temperature. Check for related history fault codes (e.g., B166711 short to ground or B166900 configuration error).
  • 2
    Turn off the ignition, disconnect the negative battery terminal, and wait at least 90 seconds (to ensure the SRS capacitor discharges). Remove the left B-pillar lower trim panel. Visually inspect the left side impact sensor for physical damage, cracks, or loose mounting.
  • 3
    Disconnect the sensor connector. Check the terminals for pin push-out, corrosion, or water ingress. Measure the terminal contact pressure. Check the wiring harness at the B-pillar bend for breakage or abrasion.
  • 4
    Reconnect the battery, turn the ignition ON, and measure the voltage at the sensor connector power supply terminal (normally 5V±0.25V reference voltage or 12V power supply, depending on the specific model). Measure the ground wire resistance (must be less than 1Ω).
  • 5
    Measure the signal line voltage (the LIN line is usually close to 12V; the CAN line should be around a 2.5V reference). If the line voltage is abnormal, check the continuity and insulation of the wiring harness to the SRS ECU in sections.
  • 6
    If the wiring tests normal, replace the left side impact sensor (Note: some models require sensor calibration or configuration coding). Tighten the sensor to the standard installation torque (usually 8-10 N·m) and secure it firmly.
  • 7
    Reconnect all connectors and clear the fault code. Use VDS to perform an SRS system self-test. Verify the left crash sensor status in the data stream displays 'Normal'. If necessary, perform a tap test to verify sensor response.
  • 8
    Perform a road test simulating bumpy road conditions to confirm the fault indicator does not illuminate again and the system has no intermittent faults.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Poor contact in the left B-pillar wiring harness caused an intermittent fault on a Qin PRO DM.

✓
A 2019 BYD Qin Pro DM. The owner reported the airbag warning light coming on intermittently, particularly after opening or closing the left front door. Used VDS to retrieve DTC B166800. Freeze frame data showed the vehicle was stationary when the fault occurred. Diagnosis found the impact sensor connector below the left B-pillar was loose, with slight oxidation on the terminals. The wiring harness retaining clip had detached, causing the harness to flex and pull repeatedly during door operation. Repair: re-secured the harness routing, cleaned the connector with dedicated terminal cleaner, applied conductive grease to prevent oxidation, and fitted a new retaining clip. Post-repair follow-up over one month showed no recurrence.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro petrol: Sensor connector pin backed out after accident repair

✓
A 2018 Qin PRO petrol variant sustained left-side damage in a collision and was repaired at a workshop. After the repair, the airbag warning light stayed on. A VDS scan showed DTC B166800. An inspection of the left side impact sensor found the power terminal (pin 1) inside the wiring harness connector had backed out, cutting off the sensor power supply. The root cause: during the collision repair, the harness plug was forced in without proper alignment, damaging the terminal retaining spring and causing the terminal to back out. Diagnostic process: measuring the sensor connector terminals found no 5V supply voltage. Tracing the wiring harness revealed the terminal had backed out at the GJK14 junction. Solution: repaired the backed-out terminal, re-crimped and reinforced the retaining spring, and seated the connector fully until it clicked. After clearing the DTC, the system returned to normal.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro DM: Sensor internal short circuit after wading

✓
A 2018 Qin Pro DM. After driving through water, the airbag warning light on the dashboard stayed on. VDS showed DTC B166800, which would not clear. The left carpet was wet. Tracing the leak found the left front sill seal had aged, allowing rainwater to get into the left side impact sensor. The sensor resistance measured 0.5Ω (normal is several thousand ohms), indicating an internal short. The wiring harness connector had water stains and verdigris. Replaced the left side impact sensor, cleaned the connector with special cleaner and blew it dry, replaced the sill seal, and added a waterproof silicone pad at the sensor mounting location. After repair, insulation resistance exceeded 10MΩ; fault resolved.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro: Loose B-pillar sensor mounting bracket causing abnormal noise and a warning light

✓
A 2019 Qin Pro petrol variant. The owner reported a clicking noise from the left front B-pillar area on rough roads, along with an intermittent airbag warning light. We initially suspected a loose B-pillar trim panel. After removing it, we traced the noise to the side impact sensor itself. Inspection found the sensor mounting bracket bolts had loosened (torque: 2 N·m vs. 10 N·m spec), letting the sensor strike the body metal on bumps. Loose solder joints on the internal accelerometer were generating the fault signal. We re-tightened the bracket bolts to the standard torque and added a rubber damping pad between the sensor and bracket to eliminate vibration transmission. After clearing the fault codes, the noise and warning light disappeared.
Original source ↗
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]