AU
B176D-00

DTC B176D-00 indicates the airbag control unit (SRS ECU) detects an open circuit or missing load in the left rear seatbelt pretensioner circuit during the system self-check — Seal U

Safety System

DTC B176D-00 indicates the airbag control unit (SRS ECU) detects an open circuit or missing load in the left rear seatbelt pretensioner circuit during the system self-check.

The SRS ECU verifies pretensioner presence by monitoring the resistance across the pretensioner squib (normal value: 1.5-3.0 Ω).

The ECU determines the pretensioner is "not present" if this resistance falls outside the threshold (open circuit >10 Ω or short circuit <0.5 Ω) or if it fails to receive the pretensioner LIN bus response signal.

This safety-critical fault prevents the left rear seatbelt pretensioner from deploying and tightening during a collision, causing a loss of restraint protection for the rear passenger.

It also continuously illuminates the instrument cluster airbag warning light.

Some models may enter fail-safe mode, limiting vehicle power output.

The B176D-00 fault code on the Seal U indicates the SRS ECU has detected an open circuit or missing load in the left rear seatbelt pretensioner circuit. Severity is medium, but it affects safety because the pretensioner may not deploy in a crash and the airbag warning light will stay on. Common causes include a faulty pretensioner igniter or loose, corroded, or damaged wiring/connectors. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Left rear seat belt pretensioner igniter internal open circuit or burnout, causing abnormal resistance (usually >10Ω or infinite).
  • 2Pretensioner wiring harness connector (located below the B-pillar or under the left side of the seat) loose, terminals backed out, oxidized from water ingress, or making poor contact; common in vehicles driven through water or from mechanical stress caused by frequent seat adjustment.
  • 3Physical damage to the wiring harness: Fore/aft seat movement chafes the harness insulation, causing a short circuit, or improper B-pillar trim panel installation pinches and severs the wiring harness, causing an open circuit.
  • 4SRS control unit internal sampling circuit fault or outdated software version causing a false report of a missing pretensioner (false fault).
  • 5Vehicle configuration data error: Failure to program the SRS system configuration after replacing the seat assembly with a non-original unit (low-spec version lacks a pretensioner), or the pretensioner model does not match the vehicle VIN.
What To Do
  • 1
    Connect VDS2000 or an equivalent diagnostic tool. Read the complete DTCs and freeze frame data. Confirm if B176D-00 is an Active or History fault. Check for other accompanying SRS fault codes (such as B176E-00 right rear pretensioner fault).
  • 2
    Perform the safe power-down procedure: turn off the ignition, disconnect the negative battery terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental pretensioner deployment during servicing.
  • 3
    Visually inspect the yellow pretensioner connector (usually marked "AIRBAG" or "SRS") inside the left rear B-pillar lower trim panel for looseness, signs of water ingress, or terminal corrosion. Clean and reconnect if necessary.
  • 4
    Disconnect the pretensioner connector. Use a digital multimeter to measure the resistance between the terminals on the pretensioner body. Standard value: 1.5-3.0 Ω (at 20°C ambient). If the reading indicates an open circuit (OL) or short circuit (0 Ω), replace the left rear seat belt pretensioner assembly.
  • 5
    Measure wiring harness continuity: Resistance between the pretensioner connector and the SRS ECU (usually located under the center console) must be <1Ω, and insulation resistance to ground and power supply must be >1MΩ. Repair any open or short circuits.
  • 6
    If wiring harness and pretensioner resistance are normal, check the SRS ECU software version and update to the latest version if necessary (some early Qin models have a false DTC bug requiring a software reflash).
  • 7
    After replacing the pretensioner, reconnect all components and restore power. Clear the fault code using the diagnostic tool and perform the "Airbag System Configuration Verification" and "Seat Belt Pretensioner Self-test" functions.
  • 8
    Perform system verification: Cycle the ignition switch 3 times. Verify the SRS warning light turns off after 6 seconds and the diagnostic tool displays the B176D-00 status as "Passed" or "Not Present".
Real-World Cases
BYD DTC AI Analysis

Qin EV450: Seat wiring harness wear causes pretensioner open circuit

✓
Qin EV450, 80,000 km. SRS warning light suddenly illuminated. VDS scan showed DTC B176D-00 (current fault). Removed the left rear seat. The wiring harness underneath had chafed against the seat rails from repeated fore-aft adjustment, wearing through the insulation and breaking the copper wires. Measured infinite resistance between pretensioner terminals; the pretensioner body itself read 2.1Ω. Replaced the damaged harness section (approx. 40 cm), wrapped it with corrugated tubing and rerouted to avoid contact with moving parts. Fault cleared, SRS light off.
BYD DTC AI Analysis

Qin 100 pretensioner connector corroded after water wading

✓
After driving through flood water approximately 40 cm deep, the instrument panel displayed an airbag malfunction. The diagnostic tool reported DTCs B176D-00 and B176E-00 (both rear pretensioner faults). Inspection found the pretensioner connector at the base of the B-pillar (yellow waterproof plug) had a perished seal. Water ingress during wading caused terminal oxidation with green copper corrosion, increasing contact resistance to 15 Ω. Cleaned the terminals with electronic cleaner, applied conductive grease, replaced the waterproof seal, and applied silicone around the connector exterior to enhance sealing. Cleared the fault codes and the system returned to normal.
BYD DTC AI Analysis

BYD Qin EV300: Configuration error after installing aftermarket seats

✓
The workshop replaced the left rear seat assembly with a used unit. The SRS warning light stayed on constantly. DTC B176D-00 indicated the pretensioner was not present. The replacement seat pretensioner measured 2.3Ω (normal) and the wiring harness continuity was normal. Investigation revealed the seat came from a base model; although it included a pretensioner, the SRS ECU configuration data showed this vehicle was not equipped with a left rear pretensioner. Solution: Using VDS, enter the SRS system special functions, perform "Vehicle Configuration Programming", change the "Left Rear Pretensioner" option to "Equipped", and execute configuration verification. Fault resolved.
BYD DTC AI Analysis

BYD Qin 80 SRS ECU software false positive fault

✓
No collision history. SRS warning light illuminated intermittently during normal use. Scan tool showed DTC B176D-00 (intermittent). Measured pretensioner resistance: 1.8Ω (normal). Wiggled wiring harness; fault would not reproduce. Checked SRS ECU software: 2016 version (outdated). Consulted TSB and confirmed this version has a false positive defect for the left rear pretensioner sampling circuit. Solution: Upgraded SRS ECU software to 2018 or later (SRS_V2.3.1 or above). Fault has not reoccurred since upgrade.
BYD DTC AI Analysis

Qin EV450 pretensioner internal squib open circuit

✓
Following a collision, the left rear seatbelt pretensioner deployed (visible creasing on the webbing). Replaced the unit, but DTC B176D-00 remained. Measured infinite resistance on the new part. Found the part was aftermarket with a cold solder joint on the internal squib. Installed a genuine pretensioner (part number: SC-8114500) and measured 2.0Ω resistance (normal). Performed airbag system self-test and passed. This case emphasizes using genuine parts only; aftermarket components may have quality defects.
Other Seal U Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U overview →
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.