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 — Seal U

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 — Seal U
  • 1After replacing the left side impact sensor (or after accident repairs), failure to perform the 'Sensor ID Learning' or 'SRS System Configuration' procedure using the BYD VDS diagnostic tool prevented the system from writing the new sensor hardware ID to the control module.
  • 2The SRS control module software version does not match the sensor hardware version. This commonly occurs due to a failed vehicle software OTA update, mixing parts across model years (e.g., installing a 2020 sensor in a 2018 vehicle), or failing to synchronize the configuration after replacing the control module.
  • 3Water ingress, oxidation, or terminal back-out at the left side impact sensor wiring harness connector (usually plug GJK inside the left B-pillar trim or plug G10 under the seat) causes a CRC check failure when reading configuration data.
  • 4EEPROM data inside the SRS control module corrupted after a vehicle collision, or sensor replaced with an unencoded aftermarket or salvaged 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). Mistakenly modifying the SRS wiring harness during vehicle modifications (such as retrofitting 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 installation of the left side impact sensor (located inside the middle-lower left B-pillar trim panel 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 panel). Measure the sensor supply voltage (should be 9-16V, ignition ON).
  • 3
    Execute the 'Airbag System Configuration' function, select 'Side Impact Sensor ID Learning', and follow the prompts to trigger the left side impact sensor (on some models, lightly tap the sensor or wait for automatic recognition). Write the sensor serial number to the SRS control module.
  • 4
    If configuration fails or the system cannot recognize the sensor, first 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 the resistance is abnormal, inspect and repair the wiring harness.
  • 5
    After successful configuration, clear all DTCs, exit the diagnostic tool, lock the vehicle, allow it to sleep for 5 minutes, then power on the vehicle. Perform the SRS self-check (the instrument cluster airbag warning lamp should turn off). Finally, use the diagnostic tool to read the data stream, verify the 'Left Side Impact Sensor Status' displays 'Configured/Normal', and perform a 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.

✓
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

✓
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 Seal U Fault Codes
B1108For 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.B1109DTC B1109 indicates an open circuit in the communication line between the air conditioning system PM2.5 air quality sensor (dust concentration sensor) and the air conditioning control unit (AC ECU), or an open circuit within the sensor internal circuitry. Typically located in the air conditioning intake duct, this sensor monitors real-time PM2.5 particle concentration inside and outside the vehicle. It provides data to the automatic air conditioning system for intelligent switching between fresh air and recirculation modes and for controlling the air purification device. During an open circuit fault, the AC ECU cannot receive the air quality signal, triggering the system fail-safe mode. Symptoms typically include failure of the automatic recirculation function, abnormal air purification indicator light operation, or abnormal air quality data displayed on the air conditioning panel. Severe cases may compromise the cabin environment control strategy, but do not directly affect vehicle driving safety.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
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]