AU
B174111

DTC B174111 indicates a short to ground in the Left Rear Side Airbag ignition circuit — Seal U

Safety System

DTC B174111 indicates a short to ground in the Left Rear Side Airbag ignition circuit.

In the SRS (Supplemental Restraint System), this means the wiring between the Airbag Control Unit (ACU) and the left rear side airbag module (typically the low-side drive wire or high-side power wire) has an abnormal electrical connection to vehicle ground (GND).

This drops the circuit resistance abnormally, typically below 1-2 ohms.

This fault causes the ACU to detect a short-circuit risk in the airbag circuit.

To prevent accidental deployment or insufficient ignition energy, the system disables the airbag and illuminates the instrument cluster airbag warning light.

The left rear side airbag typically mounts inside the C-pillar trim panel or on the side of the rear seat.

The wiring harness routes through crush-prone areas, such as the sill trim panel and seat rails, making mechanical damage a frequent cause of this fault.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Wiring harness mechanical damage: A loose or detached wiring harness retaining clip inside the left rear door sill trim panel causes the harness to rub against the seat slide rail or sharp body edges over time, damaging the insulation and causing a short circuit to the metal body.
  • 2Improper seat modification/repair: During rear seat removal/installation or leather trimming, fixing screws or clips pierce the side airbag wiring harness, causing the core wire to short to ground.
  • 3Connector water ingress and corrosion: Vehicle wading or poor floor sealing causes water ingress into the airbag connector below the left B/C-pillar (usually a yellow waterproof plug), resulting in electrolytic corrosion between the terminals and a short to ground.
  • 4Internal short circuit in the airbag module: Internal insulation failure of the clock spring or squib in the airbag assembly causes the firing circuit to short to ground.
  • 5SRS control unit internal fault: A damaged airbag drive transistor or monitoring circuit inside the ACU falsely reports a short to ground (actual external wiring is normal).
What To Do
  • 1
    Safety preparation: Set the vehicle to OFF, disconnect the low-voltage battery negative terminal, and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Fault confirmation and data recording: Use a VDS2000 or Launch X431 diagnostic tool to read complete fault codes and freeze frame data. Record parameters such as vehicle speed, temperature, and voltage when the fault occurred. Confirm B174111 is a current fault (Present), not a history fault.
  • 3
    Initial visual inspection: Remove the left rear door sill trim, lower C-pillar trim, and seat. Inspect the wiring harness for wear, cuts, indentations, or water stains, focusing on the harness routing at the seat mounting bolts.
  • 4
    Circuit section isolation test: Disconnect the ACU connector (usually under the center console or bulkhead) and the left rear side airbag module connector. Use a multimeter to measure the airbag circuit resistance to ground. Normal resistance is infinite (>10kΩ). Resistance less than 1Ω confirms a short to ground.
  • 5
    Short-circuit location: Use the half-split method to troubleshoot the wiring harness. Strip back the main harness at the midpoint to inspect or measure, gradually narrowing the short-circuit range until locating the damaged point. Common fault points are inside the sill harness corrugated conduit or in the transition area under the seat.
  • 6
    Component-level test: If the external wiring harness tests normal (good insulation to ground), directly measure the resistance to ground at the two pins of the airbag module. It should show no continuity. If continuity exists, replace the left rear side airbag assembly. (Note: Do not measure airbag resistance while energized.)
  • 7
    Repair and Replacement: Repair the damaged wiring harness (use waterproof heat-shrink tubing or replace the entire harness section). Secure the harness in place, route it correctly, and maintain sufficient clearance from the seat slide rail. If the connector is corroded, replace the connector terminals. If the airbag module or ACU is faulty, replace the corresponding component.
  • 8
    System verification: Reconnect all connectors and the battery. Clear the fault code and perform three ignition cycles (OFF-ON-ACC). Verify the SRS warning lamp turns off normally. Use the diagnostic tool to perform 'SRS System Self-test' and 'Crash Sensor Calibration' (if applicable). Verify DTC B174111 does not return and the system status displays 'Normal'.
Real-World Cases
BYD DTC AI Analysis

An aftermarket rear seat modification on a Qin Pro DM pinched the wiring harness, causing a short circuit.

✓
A 2018 Qin Pro DM logged fault code B174111. The owner reported recently having leather seat upholstery fitted at an automotive accessory market. The mechanic found a self-tapping screw beneath the left rear seat mounting bracket had pierced the wiring harness corrugated tubing, causing the black/yellow wire (ignition negative) in the airbag circuit to make direct contact with the screw (body earth). Removed the screw, repaired and re-secured the harness. Fault cleared.
BYD DTC AI Analysis

Corroded door sill wiring harness connector on water-wading vehicle

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2019 BYD Qin Pro (petrol). Airbag warning light remained on after wading through water during a typhoon. Diagnostic scanner retrieved DTC B174111. Removed the left rear sill trim panel and found the airbag harness connector below the B-pillar (yellow 2-pin plug) had obvious water staining and verdigris; terminal-to-ground resistance measured 0.3Ω. Cleaned and dried the terminals, applied conductive anti-corrosion paste, reconnected the harness, and cleared the fault code. The fault has not recurred.
BYD DTC AI Analysis

C-pillar interior trim panel improperly installed, chafed wiring harness

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After the accident repairs, the dealer replaced the left rear C-pillar trim panel. A week later, the SRS light came on. A scan revealed active fault code B174111. When the dealer removed the trim, they found the trim clip had pressed against the airbag harness during installation, damaging the insulation and exposing copper wires that contacted the vehicle body. They replaced about 30 cm of the damaged harness and rerouted the wiring away from the clip, which fixed the problem.
BYD DTC AI Analysis

Internal short circuit in left rear side airbag module

✓
2019 BYD Qin Pro DM. No accident history or modifications. SRS warning light came on suddenly. Inspected external wiring harness insulation – good. Measured continuity between ACU and airbag harness – normal, no short to ground. However, resistance between the two pins of the airbag module itself and ground measured only 0.8Ω. Diagnosed internal ignition coil insulation failure in the airbag. Replaced left rear side airbag assembly (required removing C-pillar trim). Fault cleared.
BYD DTC AI Analysis

SRS control unit internal driver circuit fault

✓
Rare case: vehicle required multiple return repairs. Despite replacing the wiring harness and airbag module, DTC B174111 persisted. An oscilloscope check of the ACU output waveform showed the channel driver transistor had shorted to ground, continuously outputting a short-to-ground signal regardless of external load. Replaced the airbag control unit (ACU) and performed coding (requires writing the vehicle VIN and crash sensor configuration parameters). This completely resolved the issue.
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.