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 — Atto 3

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.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Left rear seat belt pretensioner squib internal open circuit or burned out, causing abnormal resistance (typically >10Ω or infinite).
  • 2Pretensioner wiring harness connector (located below the B-pillar or at the lower left side of the seat) loose, terminals backed out, oxidized from water ingress, or making poor contact. Common in vehicles driven through water or due to mechanical stress from frequent seat adjustment.
  • 3Physical damage to the wiring harness: Fore-and-aft seat movement wears through the harness insulation, causing a short circuit, or improper B-pillar trim panel installation pinches and severs the harness, causing an open circuit.
  • 4SRS control unit internal sampling circuit fault or outdated software causing a false report of a missing pretensioner (false fault).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 without pretensioner), or the pretensioner model does not match the vehicle VIN.
What To Do
  • 1
    Connect VDS2000 or an equivalent diagnostic tool. Read all DTCs and freeze frame data. Confirm whether B176D-00 is a current fault (Active) or a history fault (History). Check for accompanying SRS fault codes (such as B176E-00 right rear pretensioner fault).
  • 2
    Perform the safe power-down procedure: turn off the ignition switch, disconnect the negative battery terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental pretensioner deployment during repair.
  • 3
    Visually inspect the yellow pretensioner connector (usually marked "AIRBAG" or "SRS") inside the left B-pillar lower trim panel for looseness, water ingress, or terminal corrosion. Clean and reconnect if necessary.
  • 4
    Disconnect the pretensioner connector and use a digital multimeter to measure the resistance between the pretensioner body terminals. Standard value: 1.5-3.0 Ω (at 20°C). If the multimeter reads an open circuit (OL) or short circuit (0 Ω), replace the left rear seat belt pretensioner assembly.
  • 5
    Measure wiring harness continuity: Circuit resistance from the pretensioner connector to the SRS ECU (usually located under the centre console) must be <1Ω. Insulation resistance to earth 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. Update to the latest version if necessary (some early Qin models have a false alarm bug and require a program reflash).
  • 7
    After replacing the pretensioner, reconnect all components and restore power. Use the diagnostic tool to clear the fault code 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 lamp turns off after 6 seconds and the diagnostic tool displays 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 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.