AU
B172D

DTC B172D indicates the Supplemental Restraint System (SRS) detects a short to vehicle power (B+) in the Left Second Row Side Airbag Module ignition circuit — Atto 8

Safety System

DTC B172D indicates the Supplemental Restraint System (SRS) detects a short to vehicle power (B+) in the Left Second Row Side Airbag Module ignition circuit.

During self-diagnostics or continuous monitoring, the Airbag Control Unit (ACU) detects an abnormally high voltage (near 12V battery voltage) in the left second row side airbag deployment circuit.

This exceeds the normal monitoring range (typically a low voltage or specific resistance value).

This short to power forces the airbag system into fail-safe mode, disables the affected airbag to prevent accidental deployment, and illuminates the airbag fault warning lamp.

As the second row side airbag is part of the passenger restraint system, this fault constitutes a severe safety risk.

The short circuit can prevent the airbag from deploying during a collision or, in extreme cases, trigger unintended deployment.

The B172D fault code on the Atto 8 indicates a high-severity SRS fault where the left second row side airbag ignition circuit is shorted to battery power. The airbag system may disable the affected airbag and turn on the warning lamp. Common causes include a worn or pinched under-seat harness or an internal short in the airbag module. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Under-seat harness worn or pinched: Frequent fore-and-aft adjustment of the left middle-row seat or passengers stepping on the harness damages the side airbag harness insulation, causing contact with the power wire.
  • 2Airbag module internal short circuit: The igniter bridge wire inside the left middle-row side airbag assembly shorts to the housing or power terminal, usually due to manufacturing defects or water ingress.
  • 3Connector terminal misalignment: A backed-out or bridged terminal in the yellow airbag connector under the seat (usually near the seat rail) shorts the ignition circuit terminal to the power terminal.
  • 4ACU internal fault: A fault in the airbag control unit internal drive circuit or monitoring circuit generates an incorrect short-to-power diagnosis (false report).
  • 5Improper repair procedures: During recent seat removal and installation, interior trim panel removal, or floor cleaning, a tool piercing the wiring harness or failing to fully lock the connector caused the terminal to contact the power wire.
What To Do
  • 1
    Safety Preparation: Disconnect the 12V battery negative terminal, wait at least 90 seconds to fully discharge the SRS system capacitors, wear an anti-static wrist strap, and disable the vehicle high-voltage system (for hybrid/EV models).
  • 2
    Fault Confirmation and Freeze Frame Analysis: Use a dedicated BYD diagnostic tool (VDS or ED400) to read the fault code, confirm B172D is a current fault (Active), and record the freeze frame voltage values and vehicle status at the time of the fault.
  • 3
    Visual wiring inspection: Remove the left middle-row seat. Inspect the airbag wiring harness inside the yellow protective sleeve under the seat for abrasion, cuts, or burn marks. Focus on the seat rail mounting points and the wiring pass-through grommet.
  • 4
    Connector inspection: Disconnect the airbag connector under the seat (usually marked as DAB- or SAB-related). Inspect terminals for corrosion, water ingress, or short circuits between terminals. Measure resistance between connector terminals (normal: 2.0-5.0 Ω).
  • 5
    Short circuit location: Use a multimeter to measure continuity between the airbag wiring harness side (not the module side) and the positive power supply. If continuity exists, inspect the harness in sections along its routing to locate the short circuit to the vehicle power wire (constant power or ignition power).
  • 6
    Module isolation test: Disconnect the airbag module connector and connect a dedicated airbag simulator (2Ω substitute resistor) to the circuit. Clear the fault code. If the fault disappears, the airbag module has an internal short circuit. Replace the left middle-row side airbag assembly.
  • 7
    Wiring harness repair or replacement: If the wiring harness is damaged, repair it using high-temperature tape and corrugated conduit. Maintain sufficient clearance from the power cable. If the wiring harness is severely damaged, replace the entire seat wiring harness assembly.
  • 8
    System verification: After repair, reconnect all connectors, reconnect the battery, use the diagnostic tool to clear the fault code, and perform the SRS system self-check (usually requires cycling the ignition switch ON/OFF 3 times). Confirm B172D does not return and the airbag warning light turns off. Finally, move the seat through its full fore-and-aft adjustment range to verify there is no wiring harness interference.
Real-World Cases
BYD DTC AI Analysis

Worn wiring harness for the left second-row side airbag caused B172D on a Song MAX.

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The vehicle is a 2019 Song MAX with 32,000 km. The airbag warning light stays on. Diagnostic scan tool retrieved DTC B172D (current fault). Inspection found the protective sleeve on the wiring harness beneath the second-row left seat was damaged. The harness had chafed at the seat slide rail mounting point, wearing through the internal wire insulation. The exposed wire contacted the seat heater power wire (constant power), causing a short circuit. Repaired the damaged harness, rerouted the wiring away from the seat slide rail travel path, and added an abrasion-resistant protective sleeve. Fault resolved.
BYD DTC AI Analysis

Water ingress and corrosion in the left middle-row side airbag connector on the Tang DM.

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2021 BYD Tang DM. Airbag warning light came on after the vehicle waded through water. Diagnosis revealed fault code B172D. Removed the carpet, disconnected and inspected the airbag connector under the left second-row seat. Found water stains and green terminal corrosion causing a short between terminals. Water entered through the door sill trim while wading, and the connector seal had deteriorated. Repair: cleaned and dried the connector, sprayed electronic contact cleaner, replaced the seal, and cleared the fault code. System returned to normal.
BYD DTC AI Analysis

Yuan EV side airbag module internal short circuit false alarm

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2019 BYD Yuan EV, no prior accidents. Airbag warning light suddenly came on; VDS scan showed B172D. Checked wiring harness and connectors – no damage or abnormalities. Disconnected the airbag module and tested with a simulator; fault code cleared. Reconnected the module and the fault reappeared. Diagnosed as a short to power in the igniter inside the left middle-row side airbag assembly. Replaced the OEM left middle-row side airbag module (part number matched to VIN). Programmed and configured the system; fault completely eliminated.
BYD DTC AI Analysis

Qin Pro wiring harness pinched and shorted after seat modification

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2020 BYD Qin petrol version. Owner self-installed a seat ventilation system; airbag warning light came on. Diagnosed DTC B172D. Inspection found the wiring harness was not secured properly during the modification—the new fan power wire and side airbag harness were pinched at the seat frame, causing insulation damage and a short circuit. Repair: separated and re-secured the harness using OEM harness clips to ensure clearance, and repaired the damaged insulation. Fault cleared.
Other Atto 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 overview →
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.