UK
AU
B166A00

DTC B166A00 indicates interrupted communication or abnormal data between the airbag control unit (SRS ECU) and the Left Side Impact Sensor — Atto 3

Safety System

DTC B166A00 indicates interrupted communication or abnormal data between the airbag control unit (SRS ECU) and the Left Side Impact Sensor.

This sensor typically mounts at the lower B-pillar or under the left front seat and monitors left-side impact acceleration.

A communication error prevents the ECU from receiving real-time impact data from the sensor, causing the side and curtain airbags to fail to deploy accurately during a collision, or risking unintended deployment.

This fault constitutes an active safety system failure.

The vehicle remains drivable, but side-impact protection functions degrade.

4
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM lost communication with the left sensor after wading.

✓
A 2019 BYD Qin Pro DM. Owner reported the airbag warning light stayed on constantly after driving through floodwater during a heavy rain. Scan tool read active fault code B166A00. Removed the left B-pillar trim panel and found clear water stains and green corrosion inside the sensor connector. Cleaned the connector pins with WD-40 Precision Contact Cleaner, applied conductive grease, and reassembled. The fault temporarily cleared but returned after one week. Finally replaced the wiring harness connector and sensor to fix the issue. For vehicles that have waded through water, check the floor wiring harness sealing carefully.
BYD DTC AI Analysis

Qin Pro (petrol): Sensor not configured after accident repair

✓
2018 BYD Qin Pro petrol. The airbag warning light came on after left-side accident repairs. DTC B166A00 stored. Inspection found the left front door and B-pillar sheet metal were replaced during the accident repair. The technician reinstalled the side impact sensor but forgot to connect the connector. After connecting the connector, the DTC remained. Used the BYD diagnostic tool to run the 'SRS Configuration' function, performed address configuration on the left sensor (wrote the configuration code), and cleared the DTC. Online configuration is mandatory after sensor replacement.
BYD DTC AI Analysis

Aftermarket ambient lighting caused LIN bus short circuit

✓
2020 BYD Qin Pro DM. The airbag warning light illuminated the day after the owner had interior ambient lighting fitted at the dealership. DTC B166A00. Inspection found that while routing wiring through the sill, the modification technician pierced the LIN communication line to the left impact sensor when securing a wiring clip with a screw, causing a short to earth. Repaired the damaged wiring and insulated it with heat-shrink tubing. Fault cleared. Recommendation: BYD SRS wiring is highly integrated with the body harness; avoid drilling holes or mounting foreign objects in the sill area during modifications.
BYD DTC AI Analysis

Intermittent communication failure due to sensor aging

✓
A 2018 Qin Pro DM with 120,000 km on the clock had an intermittent airbag warning light. Fault code B166A00 was intermittent. The wiring harness and connectors looked normal, but resistance at the sensor sometimes read open circuit. Replaced the left side impact sensor, but the fault remained. Finally found the sensor mounting bracket was loose, causing poor connector contact. Re-secured the bracket and added anti-vibration washers to fix the issue. On older vehicles, check the sensor bracket for deformation from chassis vibration.
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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.