AU
B166900

This fault code indicates the SRS (Supplemental Restraint System) control module detects the configuration parameters for the left side impact sensor (typically mounted on the left B-pillar, left front door intrusion beam, or under the driver's seat, depending on vehicle configuration) do not match expected system values — Atto 3

Safety System

This fault code indicates the SRS (Supplemental Restraint System) control module detects the configuration parameters for the left side impact sensor (typically mounted on the left B-pillar, left front door intrusion beam, or under the driver's seat, depending on vehicle configuration) do not match expected system values.

This is not a simple electrical open/short circuit (DTC B166800) or communication interruption (DTC B166A00).

Instead, it indicates the SRS control module EEPROM contains abnormal or missing data for the sensor's hardware ID code, calibration coefficients, software version identifier, or installation position parameters.

Specifically, the control module cannot correctly identify the sensor.

This may cause the side airbag and curtain airbag deployment thresholds to deviate from design values, or cause the system to fail to deploy during a side impact.

Common trigger scenarios include: failing to perform online configuration (coding) after sensor replacement, failing to migrate data after an SRS control module software update, using non-genuine parts (lacking vehicle configuration data), or SRS module data area damage following a collision.

This fault is a functional safety configuration error.

Repair immediately to restore normal side impact protection function.

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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1Failure to execute the 'Sensor ID Learning' or 'SRS System Configuration' procedure using the BYD VDS diagnostic tool after replacing the left side impact sensor (or after accident repairs) prevents writing the new sensor hardware ID to the control module.
  • 2The SRS control module software version does not match the sensor hardware version. Common causes include a failed vehicle software OTA update, mixing parts from different model years (for example, installing a 2020 sensor in a 2018 vehicle), or replacing the control module without synchronizing the configuration.
  • 3Water ingress, oxidation, or backed-out pins at the left side impact sensor wiring harness connector (usually the GJK plug inside the left B-pillar trim or the G10 plug under the seat), causing a CRC check failure when reading configuration data.
  • 4A vehicle collision corrupted the EEPROM data inside the SRS control module, or the sensor was replaced with an uncoded aftermarket or used part lacking valid configuration data.
  • 5Severe battery discharge, power disconnection during repairs, or incorrect jump-starting causes the SRS control module to lose stored configuration data (intermittent). Alternatively, accidentally modifying the SRS wiring harness during vehicle modifications (e.g., adding seat heating) changes bus resistance and triggers configuration protection.
What To Do
  • 1
    Connect the BYD VDS2000/VDS3100 diagnostic tool to the vehicle. Read all DTCs and freeze frame data. Confirm whether B166900 is an Active or History fault. Check for accompanying B166A00 (communication error) or B166800 (hardware fault) codes to rule out multiple faults.
  • 2
    Visually inspect the mounting status of the left side impact sensor (located inside the lower-middle trim panel of the left B-pillar or under the seat). Confirm the part number (e.g., BYD-3636900-XX) matches the vehicle model year. Check the wiring harness connector for looseness, water ingress, or oxidation (focus on the GJK connector sealing ring inside the B-pillar trim). Measure the sensor supply voltage (9-16V, ignition ON).
  • 3
    Run the 'Airbag System Configuration' function and select 'Side Impact Sensor ID Learning'. Follow the prompts to trigger the left side impact sensor (on some models, lightly tap the sensor or wait for automatic recognition) to write the sensor serial number to the SRS control module.
  • 4
    If configuration fails or the system cannot recognize the sensor, update the SRS control module software to the latest version (path: SRS system -> Programming -> Online Update) to eliminate software bugs, then retry the configuration. If the configuration still fails, measure the sensor CAN line resistance (standard 60Ω±5Ω). If abnormal, inspect and repair the wiring harness.
  • 5
    After successful configuration, clear all DTCs and exit the diagnostic tool. Lock the vehicle, allow it to sleep for 5 minutes, then power it on again. Perform an SRS self-check (the instrument cluster airbag warning lamp should turn off). Finally, use the diagnostic tool to read the data stream, confirm the 'Left Side Impact Sensor Status' displays 'Configured/Normal', and perform a light tap test to verify signal response.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

E2 EV: After replacing the left B-pillar sensor, not configuring it caused the warning light to stay on.

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Vehicle details: 2019 BYD E2, 32,000 km. The workshop replaced the left side impact sensor after accident repairs to the left front door. Symptoms: The airbag warning light on the instrument cluster stayed on. VDS read a current fault code B166900. Diagnosis: The replacement sensor was a genuine part, but the shop had not performed the configuration procedure. The control module showed the sensor ID as 'FFFFFFFF' (not learned). Repair: In the VDS airbag system, selected Special Functions > Side Sensor Configuration. Performed left side sensor ID learning. After writing the ID, cleared the fault code. The airbag warning light went out, and the data stream showed normal sensor status.
BYD DTC AI AnalysisFrom Chinese market (translated)

Intermittent B166900 fault after software upgrade on Qin Pro DM

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Vehicle: 2018 Qin Pro DM. During routine service, upgraded SRS software. Symptoms: Intermittent airbag warning light illumination the day after upgrade. Retrieved DTC B166900 (alternating between history and current). Diagnosis: Inspection found a compatibility issue between the SRS control module software version and the left side impact sensor firmware version. Sensor configuration data intermittently lost following system sleep cycles. Repair: Reflashed SRS control module software to latest stable version (non-beta). Performed full system configuration and sensor calibration. Fault did not recur.
BYD DTC AI AnalysisFrom Chinese market (translated)

E3 left B-pillar water ingress caused configuration data verification failure

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Vehicle: 2020 BYD E3. Fault occurred after driving during rainy season. Symptoms: Instrument cluster displayed 'Check SRS System'. DTCs: B166900 + B166A00. Diagnosis: Removed left B-pillar trim panel. Found green copper corrosion inside the GJK connector (black 2-pin). Sensor power supply was normal, but CAN signal interference caused a CRC error when the control module read the configuration data. Repair: Cleaned connector pins, applied conductive grease, dried the wiring harness with a blower, reconnected, and performed sensor configuration. Fault cleared. Recommendation: Check the B-pillar seal drain holes.
BYD DTC AI AnalysisFrom Chinese market (translated)

Control module data corruption on Qin EV after accident repair

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Vehicle: 2019 Qin EV. History: Left side collision; replaced left side airbag and impact sensor. Symptoms: After repair, VDS scan showed DTC B166900, unable to clear. Diagnosis: Verified new sensor works. Measured wiring continuity and resistance — normal. Configuration attempt returned 'Write Failed' error. Determined SRS control module internal EEPROM data area damaged during impact. Repair: Replaced SRS control module (requires simultaneous replacement of seatbelt pretensioners and online matching), performed full system configuration and VIN write. Fault resolved.
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]