AU
B179E00

This fault code indicates the Airbag Control Unit (ACU) detects an abnormal electrical series connection between an airbag ignition circuit (e — Atto 8

Safety System

This fault code indicates the Airbag Control Unit (ACU) detects an abnormal electrical series connection between an airbag ignition circuit (e.g., driver/front passenger frontal airbag, side airbag, or curtain airbag) and another vehicle electrical circuit (e.g., another airbag circuit, seat belt pretensioner circuit, or sensor circuit).

Normally, each ignition circuit remains independent with a specific resistance (typically 2.0 ± 0.2 Ω).

When a series connection occurs, total circuit resistance increases abnormally (combining to exceed 4 Ω) or the control unit detects cross-circuit signal interference.

This prompts the ACU to flag compromised circuit integrity.

This fault can prevent airbag deployment during a collision (due to insufficient ignition energy) or cause unintended deployment, severely compromising occupant protection.

3
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Short circuit or crossed wires between wiring harness connector terminals, particularly where moisture, oxidation, or physical damage bridges the terminals in connectors under the seat, in the steering wheel clock spring, or inside the B-pillar trim.
  • 2Airbag Control Unit (ACU) internal MOSFET drive circuit or detection circuit fault causes signal crosstalk between circuits, resulting in false detection of an external series connection.
  • 3Incorrect wiring during airbag or seat belt pretensioner replacement after accident repairs cross-connects pins from different ignition circuits, creating an electrical series circuit.
  • 4After vehicle wading or deep interior cleaning, aging connector seals create a conductive path between terminals, especially at the seat-to-floor wiring harness junction.
  • 5Wiring harness manufacturing defects or long-term wear damages the insulation, causing short circuits between adjacent wires. Using a non-OEM wiring harness during repairs causes pinout mismatches.
What To Do
  • 1
    Use the VDS2000 or VDCI diagnostic tool to read the complete DTC and freeze frame data. Identify the specific airbag circuit (e.g., driver side stage 1/stage 2 airbag, side airbag) and the associated series circuit. Record the environmental conditions (temperature, voltage) when the fault occurred.
  • 2
    Perform the airbag system power-down procedure: disconnect the battery negative terminal and wait at least 3 minutes (5 minutes recommended) to fully discharge the system. Inspect the Airbag Control Unit (ACU) connector and related airbag component connectors (focusing on areas under the seats, under the steering wheel, and the B-pillar and C-pillar areas) for water ingress, green corrosion, or deformed terminals.
  • 3
    Use a digital multimeter to measure the resistance between the pins of the faulty circuit. Normal resistance is approximately 2.0 Ω (including approximately 0.5 Ω clock spring resistance). A resistance of approximately 4 Ω confirms two circuits are in series. Measure the insulation resistance between the involved circuits. The resistance must be greater than 1 MΩ. A low resistance value indicates a short circuit.
  • 4
    If a connector is faulty, clean it with electrical contact cleaner and apply conductive protective compound; replace the connector or wiring harness if necessary. If the wiring harness has an internal short circuit, use the circuit diagram to locate and repair the damaged point, or replace the entire wiring harness section. If the ACU has an internal fault (abnormal resistance between ACU terminals), replace the airbag control unit and complete online coding, VIN writing, and crash sensor calibration.
  • 5
    After repair, clear the fault code and perform a static test (turn the ignition switch ON and verify the SRS warning lamp turns off after self-check) and a dynamic test (use the diagnostic tool to perform an actuator test and verify all circuit resistance values are within the standard range). Finally, perform a road test to verify the repair.
Real-World Cases
BYD DTC AI Analysis

Seat wiring harness series fault in water-damaged vehicle

✓
A 2019 Qin PRO DM drove through floodwater after heavy rain in Guangdong, and the dashboard displayed 'Check SRS System'. The scan tool retrieved codes B179E00 and B179D00 (passenger airbag circuit malfunction). Disassembly revealed water in the wiring harness connectors beneath the front seats; green corrosion between the terminals had connected the driver side airbag circuit in series with the passenger side pretensioner circuit. Technicians thoroughly cleaned the seat wiring harness connectors, replaced the waterproof seals, blew out the harness interior with compressed air, confirmed normal insulation resistance, then cleared the fault codes. Check wiring harness sealing at other low-lying areas of the vehicle.
BYD DTC AI Analysis

Accident repair misconnected wiring harness, causing series connection

✓
A 2018 Qin PRO petrol sustained front-end impact damage. An independent workshop replaced the driver's airbag, clock spring and seatbelt pretensioners. After the repair, the airbag warning light stayed on. Scanning revealed DTC B179E00. Inspection showed the workshop had swapped the driver's seat pretensioner connector with the side airbag connector when reconnecting the yellow plugs beneath the seat. Both connectors share identical specifications but different pin definitions, causing ignition circuit 1 and ignition circuit 2 to connect in series. Repositioned the connectors according to the service manual wiring diagram (section SRS-10) and verified that each airbag component's 2-pin plug matched the corresponding colour markings on the harness. Fault resolved.
BYD DTC AI Analysis

Clock spring internal break caused series circuit

✓
A 2019 Qin PRO DM's airbag warning light illuminated suddenly while driving; no collision history. Diagnosis revealed DTC B179E00 accompanied by B176200 (driver airbag short-to-ground history code). Steering wheel removal revealed a fractured flat cable inside the clock spring (spiral cable). The broken wire intermittently contacted other metal components during steering rotation, creating an intermittent series connection between the driver-side stage 1 and stage 2 airbag circuits. Replaced the clock spring with a genuine part (part number HA2E-5820000), calibrated the steering wheel angle sensor, and performed the 'airbag system configuration' procedure using a diagnostic tool to ensure resistance matching of the new component.
Other Atto 8 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.