AU
B176A1A

DTC B176A1A indicates the Airbag Control Unit (ACU) detects a 0-ohm resistance in the left rear seat belt pretensioner — Seal U

Safety System

DTC B176A1A indicates the Airbag Control Unit (ACU) detects a 0-ohm resistance in the left rear seat belt pretensioner.

The SRS seat belt pretensioner contains a squib with a standard resistance of 1.5-2.5 ohms.

A 0-ohm reading indicates a hard short circuit (short to ground, short to power, or internal short in the pretensioner squib).

This fault causes the ACU to identify the pretensioner circuit as abnormal.

During a collision, the pretensioner may fail to deploy and tighten the seat belt, or in extreme cases, deploy unintentionally.

Because the SRS is a critical passive safety system, this fault illuminates the airbag warning lamp and may disable related airbag functions.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Wear on the left rear seat belt pretensioner wiring harness in the seat slide rail or B-pillar area causes the conductor to short to body ground.
  • 2Water ingress, moisture, or corrosion at the pretensioner connector (usually located below the B-pillar or under the seat) causing a short circuit between terminals.
  • 3Internal short circuit in the pretensioner igniter tube (possibly due to component aging or failure to replace after a previous collision)
  • 4Airbag Control Unit (ACU) internal detection circuit fault incorrectly reporting a resistance value of 0.
  • 5Improper operation during repair, such as failing to disconnect the ACU when measuring with a multimeter on the resistance setting, or a crushed wiring harness causing a short circuit between the positive and negative terminals.
What To Do
  • 1
    Use the dedicated diagnostic tool to read the fault code, confirm whether B176A1A is a current fault (Current) or a history fault (History), and record the freeze frame data.
  • 2
    Disconnect the battery negative terminal and wait at least 90 seconds to fully discharge the SRS backup power supply and prevent accidental airbag deployment.
  • 3
    Remove the left rear B-pillar lower trim panel and locate the left rear seat belt pretensioner connector (usually a yellow connector with a short-circuit protection tab).
  • 4
    Disconnect the pretensioner connector. Use a multimeter set to ohms to measure the resistance directly between the two terminals on the pretensioner body. The standard value is 1.5-2.5 Ω. If the resistance is 0, replace the left rear seat belt assembly (integrated pretensioner and retractor).
  • 5
    If the pretensioner is normal, check the wiring harness side: measure the resistance to ground of both connector terminals and the continuity between terminals to check for a short circuit. Inspect the wiring harness for damage or crush marks.
  • 6
    Check connector terminals for deformation, backed-out pins, or water corrosion. If corroded, clean or replace the connector. If the wiring harness is damaged, repair it, reinforce the insulation, and reroute the harness to avoid interference with the seat slide rail.
  • 7
    Reconnect all connectors (ensure the short-circuit protection tab springs up), reconnect the battery negative terminal, and clear the fault code.
  • 8
    Perform an SRS system self-diagnosis, confirm B176A1A does not reappear, and check if the instrument cluster airbag warning light turns off.
  • 9
    Perform a seat belt pretensioner function test (if the diagnostic tool supports actuation tests) or perform a simulated crash signal test to verify normal system operation.
Real-World Cases
BYD DTC AI Analysis

BYD Song DM VCU Communication Fault (Wiring Harness Pin Back-Out Case)

✓
Symptoms: Multiple warning lights on. No communication with Vehicle Control Module. Vehicle undrivable. Diagnosis: Scanned fault codes; found Vehicle Control Module communication error. Checked power and CAN lines; traced to pins G09-14/15. Backed-out pin at GJK14 harness connector caused the interruption. Fuse F4/9 was intact. Resolution: Repaired the backed-out pin, reconnected the harness connector, cleared fault codes. System returned to normal. Note: Backed-out pins or poor contact in wiring harness connectors can mimic resistance-related faults.
Original source ↗
BYD DTC AI Analysis

比亚迪秦气囊系统故障（座椅传感器线束磨损）

✓
症状：仪表安全气囊故障灯常亮，系统提示安全气囊故障。诊断过程：连接诊断仪读取故障码，发现座椅占用传感器相关故障；检查座椅下方传感器线束连接器；测量传感器供电电压和信号线电阻；发现线束在座椅滑轨处磨损导致间歇性短路。解决方案：修复受损线束，重新固定线束走向，避免与运动部件干涉，更换受损的座椅占用传感器。该案例与预紧器故障类似，均为座椅区域线束磨损导致的短路故障。
Original source ↗
BYD DTC AI Analysis

BYD HA EPS System Fault (Abnormal Sensor Resistance Reference)

✓
Symptoms: Heavy steering, EPS warning light illuminated on the instrument panel, and intermittent power steering assistance. Diagnosis: Retrieved DTC C1B1700 indicating motor temperature sensor fault. Checked EPS ECU supply voltage (specification 10-16V). Inspected torque sensor signal wiring for open or short circuits. Measured motor temperature sensor resistance — out of spec. Repair: Replaced the steering gear assembly (integrated EPS motor and ECU), cleared fault codes, and ran system self-diagnosis to confirm the fault cleared. This case demonstrates diagnostic methods for sensor resistance abnormalities (including short circuits), providing reference for troubleshooting pretensioner resistance faults reading zero ohms.
Original source ↗
BYD DTC AI Analysis

BYD Qin Battery Management System Communication Fault (CAN Bus Short Circuit Troubleshooting Reference)

✓
Symptoms: Vehicle unable to engage high voltage; instrument cluster displayed powertrain fault and charging indicator was abnormal. Diagnostic process: Scan tool retrieved BIC communication timeout DTCs (U20B000 series). Checked CAN communication lines between battery manager and BIC (Battery Information Collector). Measured BIC supply voltage and found abnormal supply at some BIC modules. Inspected high voltage interlock circuit and confirmed high voltage interlock 2 fault (P1AC200). Solution: Repaired high voltage interlock wiring, replaced damaged BIC modules, updated battery manager software, and recalibrated battery system. This case demonstrates systematic troubleshooting for wiring shorts and communication faults.
Original source ↗
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.