AU
B17731B

This DTC indicates the SRS (Supplemental Restraint System) control module detects a missing signal or communication interruption from the right rear seat belt pretensioner during self-check or real-time monitoring — Seal U

Safety System

This DTC indicates the SRS (Supplemental Restraint System) control module detects a missing signal or communication interruption from the right rear seat belt pretensioner during self-check or real-time monitoring.

Specifically, the control module cannot identify the pretensioner’s electronic identification (resistance signature code or LIN/CAN node ID) or detects an open circuit, short to ground, or short to power.

This prevents the seat belt at this position from tightening automatically during a frontal collision, increasing passenger forward displacement and significantly reducing restraint system effectiveness.

The SRS system also illuminates the airbag fault warning lamp and may disable the related collision trigger logic.

This is a critical fault affecting passive safety.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Right rear seat belt pretensioner connector (located below the B-pillar or under the seat) is loose, oxidized, corroded, or has backed-out terminals, causing excessive contact resistance or signal interruption.
  • 2Open circuit or resistance drift beyond the calibrated range (normal: 2.0-5.0Ω) in the pretensioner body internal squib, causing it to fail the SRS module safety check.
  • 3Long-term wear or pinching of the floor or B-pillar wiring harness at the door sill trim bend causes a wire break, resulting in an open circuit between the pretensioner and the SRS module.
  • 4Incorrect vehicle software configuration parameters, such as flashing the SRS module with a high-spec version on a low-spec vehicle lacking this pretensioner, or a hardware configuration mismatch after installing a used part.
  • 5Water ingress from wading or liquid spills in the rear causes a short circuit and corrosion inside the pretensioner connector, or poor sealing below the B-pillar allows water to enter the wiring harness connector.
What To Do
  • 1
    Safety preparation: Turn off the ignition switch, disconnect the low-voltage battery negative terminal, wait at least 90 seconds to ensure the SRS capacitor fully discharges, and wear an anti-static wrist strap. Never use a standard multimeter resistance setting to directly measure the pretensioner connected to the control module.
  • 2
    Visual inspection: Remove the right rear door sill trim panel and lower B-pillar trim panel. Check the pretensioner connector for looseness, water ingress, or deformed pins. Apply conductive grease and reseat the connector to ensure good contact.
  • 3
    Circuit continuity test: Disconnect the SRS control module and pretensioner connectors. Use a multimeter to measure wiring harness continuity between them. Inspect the harness insulation for damage, focusing on the sill bend. Repair any open or short circuits.
  • 4
    Resistance measurement: Use a dedicated SRS resistance meter (or a multimeter on the low-resistance range) to directly measure the pretensioner unit resistance. The standard value is 2.0-5.0 Ω. Infinity indicates an open circuit; replace the pretensioner. 0 Ω indicates a short circuit; check the wiring harness.
  • 5
    Configuration verification: Connect the VDS2000 or Launch X431 diagnostic tool, access the SRS system, and read the vehicle configuration code (VCU configuration or SRS configuration). Compare the code with the actual installed hardware. Rewrite the configuration parameters or update the SRS software if necessary.
  • 6
    Component replacement: If confirming the pretensioner is damaged, replace it with a pretensioner assembly of the same model (record the old part's resistance value for reference). Perform configuration calibration after replacement.
  • 7
    System Reset and Verification: After repair, reconnect the battery, clear the fault code, and perform the SRS system self-check cycle (Ignition ON-OFF three times). Verify the fault code does not return and the airbag warning lamp turns off. Use the diagnostic tool to read the live data stream and verify the channel resistance value is within the normal range.
Real-World Cases
BYD DTC AI Analysis

Worn right rear door sill wiring harness causing intermittent fault codes

✓
A 2019 BYD Qin EV developed an intermittent airbag warning light. Scanning revealed DTC B17731B. Inspection found the right rear door frame seal had deteriorated and the sill trim panel clips were loose, allowing the wiring harness to chafe through at the sill bend. The copper conductors had partially fractured, causing intermittent contact. Re-wrapped the wiring harness, secured the routing to avoid interference with the trim panel, and replaced the sill clips. Fault resolved.
BYD DTC AI Analysis

Loose connector caused signal interruption

✓
2020 E3. Rear passengers reported a seat belt malfunction. Scan tool showed B17731B. Disassembly found the right rear seat belt pretensioner connector wasn't fully locked—the terminal had backed out approximately 2mm, likely from a previous carpet repair that didn't fully seat it. Reinserted the connector, confirmed the locking tab engaged, cleared the fault code, and ran multiple bump tests with no recurrence.
BYD DTC AI Analysis

Software configuration error triggered false alarms

✓
A 2019 E2 persistently stored DTC B17731B after collision repairs. Inspection revealed this base model lacked a right rear seatbelt pretensioner from the factory, but the shop had replaced the SRS control module with a high-spec unit. The module set a fault during self-check when it could not detect the hardware. We used VDS2000 to access the SRS system and changed the vehicle configuration to "no right rear pretensioner". The fault code cleared and the system returned to normal.
BYD DTC AI Analysis

Internal open circuit in pretensioner

✓
A 2019 Qin EV. Airbag warning light stayed on after the vehicle waded through water. Inspection found the right rear carpet wet; the pre-tensioner connector contained water and green copper corrosion. Cleaning the connector didn't clear the fault. Resistance measured infinite (open circuit), indicating the internal igniter had corroded open. Replaced the right rear seatbelt assembly (including pre-tensioner) and dried/treated the wiring harness for corrosion. Fault resolved.
BYD DTC AI Analysis

Aftermarket seat covers pinched the connector.

✓
A 2020 E3 triggered DTC B17731B after the owner fitted full-surround seat covers. Inspection found the seat cover retaining clips were excessively thick and crushed the right rear seat pretensioner harness connector during installation, fracturing the connector housing and bending the pins, creating a short. Straightened the pins, replaced the connector housing, and repositioned the seat covers to avoid the wiring harness. Fault cleared.
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.