AU
B179B-00

This DTC indicates the front passenger seat belt pretensioner Stage 2 squib circuit is shorted to vehicle power positive (B+) — Seal U

Safety System

This DTC indicates the front passenger seat belt pretensioner Stage 2 squib circuit is shorted to vehicle power positive (B+).

Modern vehicle seat belt pretensioners typically use a dual-stage ignition design: the first stage deploys during the initial collision phase to provide basic restraint, and the second stage deploys upon detecting a more severe collision to increase protective force.

A short to power indicates an abnormal high-potential path in the squib circuit, which may cause: 1) The pretensioner to deploy unintentionally in non-collision situations, causing personal injury and property damage; 2) The Airbag Control Unit (ACU) to detect abnormal circuit voltage and enter fail-safe mode, disabling the front passenger airbag and pretensioner functions; 3) Continuous short-circuit current to damage the internal ACU driver circuit or trigger fuse protection.

This constitutes a severe electrical fault in the passive safety system and requires immediate repair.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Abrasion of the SRS wiring harness sleeve under the front passenger seat or inside the B-pillar causes the pretensioner drive wire to short to the power supply wire (constant power or ignition power).
  • 2Power MOSFET breakdown or drive chip failure in the airbag control module (ACU) internal ignition drive circuit, causing a continuous high-level output at the ignition terminal.
  • 3Frequent seat rail adjustment pinches and bends the pretensioner wiring harness secured under the seat, damaging the insulation and causing a short circuit to the vehicle frame or a power wire.
  • 4Short circuit between the internal igniter charge of the front passenger seat belt pretensioner assembly and the metal housing, or water ingress or corrosion at the connector terminals causing a short circuit between the positive and negative terminals.
  • 5Vehicle wading, liquid spills, or improper car washing causes water ingress at the under-seat pretensioner connector (typically located below the B-pillar or inboard of the seat), creating an electrolytic conductive path between the terminals.
What To Do
  • 1
    Safety Preparation: Disconnect the 12V battery negative terminal and wait at least 3-5 minutes for the SRS system energy storage capacitor to fully discharge. Wear an anti-static wrist strap. Do not use a standard multimeter to directly measure the ignition circuit (use a dedicated airbag resistor or diagnostic tool).
  • 2
    Visual inspection: Remove the front passenger B-pillar lower trim panel and seat (if necessary). Inspect the seat belt pretensioner wiring harness (wrapped in yellow corrugated conduit) for obvious wear, damaged insulation, or burn marks. Focus on the harness fixing points and bent sections near the seat slide rail.
  • 3
    Circuit isolation check: Disconnect the connector between the ACU and the pretensioner. Use a digital multimeter (high-impedance mode) to measure the voltage between each terminal on the pretensioner-side connector and body ground (should be 0V). Measure the resistance between each terminal and the positive power supply (should be greater than 1MΩ) to check for a short circuit to power.
  • 4
    Pretensioner unit inspection: Measure the pretensioner unit resistance (normal value approx. 1.5-2.5 Ω; refer to the workshop manual for exact specifications). If the resistance is abnormally low or shows continuity, replace the pretensioner assembly.
  • 5
    Wiring harness repair: If the wiring harness is damaged, use dedicated heat-shrink tubing or replace the entire SRS wiring harness. Do not simply wrap the harness with insulating tape. Verify the ground wire connection under the seat is secure to rule out an indirect short circuit.
  • 6
    Module-level verification: If the wiring harness and pretensioner are normal, check the ACU connector pins for deformation, push-out, or corrosion. If necessary, verify the ACU by substitution. Perform coding and configuration after replacement.
  • 7
    System reset and test: Reconnect all connectors and turn on the power. Use a BYD VDS2000/3000 or Launch X431 diagnostic tool to clear the fault code. Perform an SRS system self-check and a seat belt pretensioner function test. Verify DTC B179B-00 does not return and the airbag warning light turns off normally.
Real-World Cases
BYD DTC AI Analysis

Frequent seat adjustment caused wiring harness chafing and short circuit

✓
Model: 2018 BYD Qin EV450. Symptoms: Airbag warning light constantly illuminated on the instrument cluster. DTC B179B-00 stored. Diagnosis: Found the SRS wiring harness (yellow) beneath the front passenger seat rubbing against the metal seat rail edge when the seat was in its foremost position. The insulation had worn through, exposing the copper wiring that contacted the seat heater power cable (red), causing a short circuit. Repair: Replaced the dedicated SRS wiring harness between the floor harness and the pretensioner. Repositioned the harness clips and added abrasion-resistant sleeving to prevent pinching during full seat travel. Cleared the fault codes and road tested. Fault resolved.
BYD DTC AI Analysis

B-pillar pretensioner connector corroded from water ingress

✓
Vehicle: BYD Qin 100 2017 model. Symptoms: Airbag warning light on after driving through water; diagnostic tool showed code B179B-00. Diagnosis: Removed the front passenger side B-pillar lower trim and found the pretensioner connector (2-pin yellow plug) had obvious water stains and green corrosion. Insulation resistance between terminals dropped to approximately 200Ω, creating a soft short to power. Cause: Deteriorated door seal allowed rainwater to leak into the B-pillar cavity. Repair: Cleaned the connector with electronic cleaner, applied conductive grease after drying, replaced the waterproof sealing ring, and sealed around the connector with waterproof tape. Also replaced the slightly oxidised pretensioner terminals.
BYD DTC AI Analysis

Internal driver fault in airbag control module

✓
Model: 2017 BYD Qin 80. Symptoms: No collision history, but airbag warning light comes on intermittently. DTC B179B-00 appears sporadically. Diagnosis: Measured pretensioner harness resistance and insulation; both normal. Wiggled harness—fault did not appear. Disconnected pretensioner plug and measured at ACU side: found intermittent continuity (approx. 50-200 Ω) between ignition drive terminal and battery positive. Identified as poor thermal stability of ACU internal drive circuit or dry solder joint. Repair: Replaced airbag control module (ACU) and wrote vehicle configuration (VIN matching, sensor configuration, etc.). Fault eliminated.
BYD DTC AI Analysis

Front passenger pretensioner internal short circuit

✓
Vehicle: BYD Qin EV300 2017. Symptoms: SRS warning light comes on immediately at startup. DTC B179B-00 will not clear. Diagnosis: Disconnected the pretensioner connector. Resistance across the pretensioner terminals measured 0.3Ω (abnormally low; normal is ~2Ω). Continuity present between terminals and pretensioner metal housing. Internal short between igniter and housing. Repair: Replaced front passenger seatbelt assembly (including pretensioner). New component resistance: 2.1Ω. Cleared DTC after installation. System self-test passed. Probable cause: Insulation material defect from manufacturing or previous external impact.
BYD DTC AI Analysis

Power supply short from aftermarket seat heater installation

✓
Vehicle: 2018 BYD Qin EV450. Symptoms: B179B-00 DTC after adding seat ventilation/heating to the passenger seat. Diagnosis: The shop bundled the heating pad power feed (constant power) with the SRS pretensioner harness beneath the seat without insulation. Road vibration chafed through the power wire insulation, shorting it to the igniter wire inside the pretensioner harness. Repair: Restored factory harness routing, rerouted the retrofit circuits separately with an inline fuse, and protected them with OEM-spec corrugated tubing. Code cleared. Warning: Non-OEM electrical modifications are strictly prohibited near SRS harnesses.
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.