AU
B174A-00

This fault code indicates the measured resistance of the left rear side airbag (Side Airbag, Left Rear) firing circuit is 0 ohms, confirming a short circuit — Seal U

Safety System

This fault code indicates the measured resistance of the left rear side airbag (Side Airbag, Left Rear) firing circuit is 0 ohms, confirming a short circuit.

In the BYD SRS (Supplemental Restraint System), normal airbag squib resistance ranges from 1.5 to 3.5 ohms.

A 0-ohm reading indicates a direct short circuit between the firing circuit power wire (Squib+) and ground wire (Squib-), or the airbag module detects abnormally low internal resistance.

This condition causes the SRS control unit to identify an unintended deployment risk, illuminate the airbag warning light, and disable the left rear side airbag.

Unlike a "resistance too high/open circuit" fault (infinite resistance), damaged wiring insulation, connector water ingress, or mechanical damage typically causes short circuits.

Inspect the circuit immediately to prevent potential overheating.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Water ingress, moisture, or oxidation at the left rear seat side airbag connector (usually located under the seat or inside the C-pillar trim panel) causes a short circuit between the metal terminals.
  • 2The rear seat adjustment mechanism, seat belt mechanism, or a foreign object chafed the airbag wiring harness under the seat or inside the B/C-pillar trim panel, damaging the insulation and causing the positive and negative conductors to short circuit.
  • 3Rear passengers stepping on the side of the seat, placing heavy objects causing compression, or fixing clips piercing the wiring harness during seat modifications (leather retrimming or installing seat covers), causing an internal short circuit in the harness.
  • 4Internal short circuit in the left rear side airbag module igniter (very rare, usually exhibits airbag internal short-circuit resistance characteristics)
  • 5SRS control unit (ACU) internal detection circuit fault or bent connector pins causing a short circuit, resulting in a false 0 Ω resistance reading.
What To Do
  • 1
    Use the BYD VDS2000/2100 diagnostic tool to read the fault code. Confirm B174A-00 is 'Active'. Record the voltage and ambient temperature from the freeze frame data.
  • 2
    Perform safety procedure: Turn off the ignition, disconnect the negative battery terminal, and wait at least 90 seconds (to fully discharge the SRS capacitor and prevent accidental airbag deployment).
  • 3
    Remove the left rear seat assembly (usually requires removing 4 retaining bolts and lifting the seat), then locate the side airbag module connector (yellow connector with short-circuit protection tab).
  • 4
    Disconnect the airbag connector. Use a digital multimeter (minimum 10 MΩ input impedance) to measure the resistance between the two terminals of the airbag assembly. Normal resistance is 1.5–3.5 Ω. If the reading is 0–0.5 Ω, replace the airbag. If normal, the fault is in the wiring harness.
  • 5
    On the wiring harness side: Measure the resistance between each of the two connector terminals and body ground (should be infinite), and the resistance between the two terminals (should be infinite). If continuity exists, the circuit is shorted.
  • 6
    Inspect the airbag wiring harness outer sheath along the routing path (usually along the seat rail, lower B-pillar trim panel, and floor harness channel). Focus on interference points at the seat adjustment mechanism and harness retaining clips. Repair any damage using heat-shrink tubing or replace the harness section.
  • 7
    Check the inside of the connector for metal debris, liquid, or deformed terminals. Clean with electrical contact cleaner and verify the shorting bar functions correctly.
  • 8
    Restore all connections, reconnect the battery, and clear the fault code. Perform the 'ignition cycle test' (ON-OFF 3 times) and the 'SRS system self-test'. Confirm the fault code does not return and verify the instrument cluster airbag warning light turns off.
Real-World Cases
BYD DTC AI Analysis

Water ingress under the left rear seat caused the connector to short-circuit.

✓
A 2018 Qin EV450 came in with the airbag warning light on. Inspection found damp carpet under the left rear seat, likely from a spilled drink or water leaking past a poor window seal. Removing the seat revealed obvious water marks inside the yellow airbag connector. The terminals had micro-shorting from electrolyte corrosion, with resistance measuring 0.3Ω. The technician cleaned the connector with electrical contact cleaner, dried it, and the resistance returned to normal. They also traced the water ingress to a blocked left rear window drainage channel; clearing the drain holes resolved the fault.
BYD DTC AI Analysis

Aftermarket genuine leather seats pierced airbag wiring harness.

✓
2017 BYD Qin 100. After the owner had the seats reupholstered in leather at a custom trim shop, fault code B174A-00 appeared. Inspection found the trimmer used excessively long staples or clips to secure the leather, piercing the left rear seat side airbag harness (inside the seat back side trim) and shorting the positive and negative wires. Replaced the damaged harness section from the airbag connector to the floor harness connection point, re-routed the wiring properly, and secured it with dedicated harness clips to avoid contact with the seat frame. Fault resolved.
BYD DTC AI Analysis

Worn wiring harness at rear seat folding mechanism

✓
A Qin EV300 with 80,000 km developed intermittent fault codes. Inspection revealed that at the pivot of the left rear seat folding mechanism (40/60 split), the airbag wiring harness had been flexing repeatedly as the seat folded and unfolded. This caused fatigue damage to the insulation, exposing the copper core, which then contacted the seat's metal frame and created a short circuit. Released slack in the wiring harness, fitted protective corrugated tubing at the flex point, repositioned the harness mounting points to clear moving parts, and wrapped the area with felt tape to prevent squeaks.
BYD DTC AI Analysis

Loose connector; metal debris caused short circuit

✓
2017 Qin 80. After driving over rough roads, the airbag warning light illuminated. Found the airbag connector under the left rear seat not fully locked (possibly not fully seated during a previous repair). A small metal circlip had fallen into the connector (likely from the seat installation process), causing a short between the terminals. Removed the foreign object, confirmed the CPA (connector position assurance) was intact, reseated the connector with an audible click, and cleared the DTCs. Fault resolved.
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.