AU
B174B1A

This DTC indicates the left rear side airbag squib resistance falls below the normal threshold set by the SRS control module (ACU) (typically below 1 — Atto 8

Safety System

This DTC indicates the left rear side airbag squib resistance falls below the normal threshold set by the SRS control module (ACU) (typically below 1.2Ω-1.5Ω; standard range is generally 1.5Ω-3.5Ω).

Low resistance usually indicates a short circuit in the squib circuit.

Possible causes include a wiring harness short to ground, a wire-to-wire short, an internal connector short, or an internal short within the airbag module itself.

This fault causes the SRS system to classify the airbag as unsafe.

The airbag may fail to deploy during a collision (as the system may disable the circuit to prevent accidental deployment), or it poses a risk of unintended deployment.

This is an active safety system fault requiring immediate repair.

3
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Left rear side airbag igniter internal short circuit (gas generator fault)
  • 2Wiring harness wear under the seat or inside the C-pillar trim causes a wire short to ground or a short between positive and negative wires.
  • 3Water ingress, oxidation, or bent pins in the airbag wiring harness connector (usually located under the seat) causing abnormal continuity
  • 4SRS control module (ACU) internal detection circuit fault falsely reporting abnormal resistance
  • 5Vehicle wading or improper interior cleaning causes moisture and a short circuit in the airbag circuit connector.
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal and wait at least 3 minutes to fully discharge the SRS system capacitors and prevent accidental airbag deployment.
  • 2
    Visual inspection: Remove the left rear seat and lower C-pillar trim panel. Check the side airbag wiring harness connector for looseness, water ingress, corrosion, or backed-out pins.
  • 3
    Resistance measurement: Disconnect the airbag from the wiring harness. Use a digital multimeter to directly measure the resistance across the airbag igniter terminals (standard value: 1.5-3.5Ω; if <1.2Ω, replace the airbag).
  • 4
    Wiring harness inspection: Measure resistance to ground and check for shorts to power at each terminal of the harness-side connector. Inspect the wiring harness for signs of crushing, abrasion, or damaged insulation.
  • 5
    Insulation repair: If the wiring harness shows damage, repair it using insulating tape or heat-shrink tubing. Replace the wiring harness assembly if necessary.
  • 6
    Component Replacement: If the airbag resistance is abnormal, replace the left rear side airbag module (follow explosive handling procedures).
  • 7
    System reset: Connect all components, turn on the power, use the VDS2000/3000 diagnostic tool to clear the fault code, perform an SRS system self-check, and confirm the fault is resolved.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro DM: Left rear airbag harness pin backed out, resulting in low resistance

✓
The airbag warning light illuminated intermittently while driving. Read DTC B174B1A. Inspection found pins 14 and 15 of airbag connector G09 beneath the left rear seat had backed out, causing poor contact and intermittent short circuits, resulting in low and unstable resistance readings. Reseated the pins, ensured the connector locks were intact, cleared the DTC, and resolved the fault.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin Pro seat adjustment chafed the airbag wiring harness, causing a short circuit.

✓
Owner reported the airbag warning light came on after adjusting the left rear seat position. Diagnosis found the wiring harness interfering with the seat rail. Long-term friction wore through the insulation, causing a short to ground with low resistance (measured 0.8Ω). Repaired the harness, rerouted the wiring, and added harness clips to keep it clear of the seat mechanism. Fault resolved.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

False internal fault report in Qin Pro SRS control module

✓
Vehicle had no collision history but logged frequent B174B1A faults. Measured airbag and harness resistance at 2.1 Ω (normal). Diagnosed an internal sampling circuit fault in the SRS ECU causing false low-resistance readings. Replaced the airbag control module (ACU), recoded and calibrated the seat occupancy sensor. Fault has not returned.
Original source ↗
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. Sources: [1]