AU
B172C11

DTC B172C11 indicates the SRS (Supplemental Restraint System) detected an abnormally low-resistance path from the left second-row side airbag ignition circuit (usually the left B-pillar side airbag or seat side airbag) to body ground (GND), with a resistance typically <1Ω — Seal U

Safety System

DTC B172C11 indicates the SRS (Supplemental Restraint System) detected an abnormally low-resistance path from the left second-row side airbag ignition circuit (usually the left B-pillar side airbag or seat side airbag) to body ground (GND), with a resistance typically <1Ω.

The airbag system ignition circuit features a dual-circuit redundant design (high side and low side).

Under normal conditions, resistance to ground should be >100kΩ.

Upon detecting a short to ground, the SRS ECU identifies a risk of unintended deployment or failure to deploy.

The ECU immediately illuminates the airbag fault warning lamp and disables that side airbag and any linked restraint systems (such as the seatbelt pretensioner).

This is a hard short circuit, not an intermittent fault.

Repair immediately for occupant safety.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Wiring harness wear inside the left B-pillar trim panel: Long-term driving on rough roads or repeated removal and installation of the B-pillar trim panel causes the side airbag wiring harness (usually wrapped in yellow corrugated conduit) to rub against sharp metal body edges. This damages the insulation and allows the copper core to directly contact the chassis ground.
  • 2Under-seat wiring harness pinched and shorted: On vehicles equipped with seat side airbags, dynamic movement between the seat fore-aft adjustment mechanism and the floor harness fixing point causes the seat slide rail to pinch or chafe the harness sleeve, resulting in a short to ground.
  • 3Connector water ingress and corrosion: An aging left front door seal or leaking window allows water to enter the airbag wiring harness connector at the A/B-pillar junction (usually located inside the sill trim panel). This forms an electrolytic conductive path between the pins, causing a short to ground.
  • 4Airbag module internal short circuit: Damaged insulation on the igniter bridge wire inside the side airbag inflator (due to a manufacturing defect or long-term high-temperature aging) causes the bridge wire to short to the metal housing. Replace the entire airbag module.
  • 5SRS ECU internal drive circuit fault: ECU internal high-side or low-side drive MOSFET breakdown causes the output terminal to conduct to ground. This condition usually triggers simultaneous short circuit faults in multiple airbag circuits.
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal and wait at least 90 seconds (to ensure the SRS capacitor fully discharges). Wear an anti-static wrist strap. Prepare a dedicated diagnostic tool (such as BYD VDS 3000 or Launch X-431) and a multimeter.
  • 2
    Freeze frame analysis: Connect the diagnostic tool to read the DTC freeze frame data. Record vehicle speed, temperature, voltage, and other information when the fault occurred to determine whether it is a continuous fault (current DTC) or a history fault.
  • 3
    Visual inspection: Remove the left B-pillar lower trim panel, sill trim panel, and seat (if applicable). Inspect the yellow airbag wiring harness for obvious damage, crushing, water stains, or corrosion. Focus on contact points between the wiring harness and the body metal.
  • 4
    Circuit measurement: Disconnect the connector between the SRS ECU and the side airbag module. Use a multimeter to measure the resistance between the harness-side connector pins (usually 2 pins, high side and low side) and body ground. The normal reading is infinity (OL). A reading of 0-5 Ω confirms the wiring harness is shorted to ground.
  • 5
    Section-by-section troubleshooting: Use the bisection method to inspect the wiring harness. Measure at the airbag module connector. If the short circuit disappears, the fault lies in the wiring harness. If the short circuit persists, check the ECU side. For the seat side airbag, inspect the mating connector between the seat wiring harness and the floor wiring harness.
  • 6
    Repair or replace: If the wiring harness is damaged, repair it using heat-shrink tubing or insulating tape, and re-secure the harness to prevent further chafing. If the connector is corroded, clean or replace the connector. If the airbag module has an internal short circuit, replace it with a genuine airbag module (repair prohibited).
  • 7
    System verification: Reconnect all connectors, connect the battery, and use the diagnostic tool to clear the fault code. Perform the SRS system self-check (normally, the self-check lamp illuminates for 6 seconds and then turns off after turning the ignition switch ON). Perform static and dynamic road tests to confirm B172C11 does not return and the airbag warning lamp operates normally.
Real-World Cases
BYD DTC AI Analysis

E2: Left B-pillar wiring harness chafing caused intermittent short circuit

✓
A 2019 BYD E2 with 30,000 km on the odometer developed an intermittent airbag warning light on the instrument cluster. The scan tool read current fault code B172C11. Removed the left B-pillar trim and found the side airbag wiring harness had chafed through at the retaining clip due to prolonged vibration, exposing the copper core and contacting the body shell. Wrapped the damaged section with insulating tape, rerouted the harness to increase slack, and replaced the retaining clip to eliminate sharp edge contact. Followed up for one month after the repair with no recurrence.
BYD DTC AI Analysis

Qin EV seat rail crushed side airbag wiring harness

✓
2020 BYD Qin EV. Customer reported the airbag warning light illuminated after adjusting the seat position. Technicians found the left front seat side airbag harness (floor harness section) pinched under the seat slide rail mounting bolt, with damaged insulation causing a short to ground. Root cause: The dealer did not follow the standard harness routing when previously replacing the carpet. Repair: Replaced the damaged harness section (from main harness to seat connector), rerouted it along the floor harness channel per the workshop manual, secured it with dedicated harness clips, and ensured no interference throughout the full seat travel range.
BYD DTC AI Analysis

Water leak from E3 left front door caused connector corrosion.

✓
A 2020 E3 showed fault code B172C11 after the rainy season. We found green copper corrosion inside the airbag wiring harness connector (C-03) located within the left A-pillar lower sill trim. Pin 3 (low side drive) showed continuity with the connector housing. We traced the leak to a perished left front door seal that let rainwater seep in, run down the B-pillar, and pool at the connector. We replaced the damaged connector (including terminals), dried the affected harness bundle, fitted a new left front door seal, applied waterproof silicone grease to the connector, and properly seated the waterproof plug.
BYD DTC AI Analysis

Side airbag module internal short circuit false alarm

✓
2019 BYD Qin EV. After accident repairs, replaced the left second-row side airbag. After installation, DTC B172C11 logged. Checked wiring harness ground insulation — normal, resistance >10 MΩ. Disconnected the airbag module and measured 0.3 Ω between the igniter pin and module casing, confirming an internal manufacturing defect in the new module causing a short to ground. Fitted another genuine airbag module, fault cleared. Tip: Protect airbag modules from static electricity and mechanical shock during transport and storage. Before installation, measure igniter resistance with a multimeter (normal: 2–3 Ω, infinite to ground).
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.