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B174212

DTC B174212 indicates the SRS (Supplemental Restraint System) electronic control unit detects an abnormally low-resistance connection between the left rear side airbag squib circuit (typically installed in the left rear C-pillar or left rear door frame side panel) and the vehicle power supply positive terminal (B+) — Atto 3

Safety System

DTC B174212 indicates the SRS (Supplemental Restraint System) electronic control unit detects an abnormally low-resistance connection between the left rear side airbag squib circuit (typically installed in the left rear C-pillar or left rear door frame side panel) and the vehicle power supply positive terminal (B+).

Under normal conditions, the airbag squib circuit remains in a high-resistance open state.

The SRS ECU momentarily closes the circuit only during a collision to release current and ignite the gas generator.

A short to power causes: 1) The airbag to fail to deploy during a collision (the power supply bypasses the current, preventing sufficient heat generation to ignite the squib). 2) A potential risk of unintended airbag deployment in extreme cases due to the circuit fault (although modern SRS systems typically feature shorting bars and dual-stage trigger protection).

Affected components include the left rear side airbag module, C-pillar/floor wiring harness, seat wiring harness (if the seat integrates the airbag), and the SRS ECU.

As a Level 3 fault (the highest safety classification), the system immediately illuminates the instrument cluster airbag warning lamp and disables the entire airbag system.

The B174212 fault code on the Atto 3 indicates a high-severity SRS fault where the left rear side airbag squib circuit has an abnormally low-resistance short to battery positive. This can disable the airbag system and turn on the airbag warning light. Common causes include damaged wiring under the left rear seat or C-pillar trim, or an internal short in the airbag module. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1Wiring harness wear under the left rear seat or inside the C-pillar trim panel: During long-term vehicle use, seat fore/aft adjustment or friction from C-pillar trim clips damages the airbag wiring harness insulation, causing the copper core to directly contact the vehicle body metal frame or a power wire.
  • 2Left rear side airbag module internal igniter short circuit: Moisture in the gas generator internal igniter charge or a manufacturing defect causes the ignition resistance wire to short to the housing.
  • 3Connector water ingress or terminal corrosion: Driving through water, car washing, or poor window seals allow water to enter the left rear airbag wiring harness connector (usually yellow), forming an electrolytic conductive path between the terminals.
  • 4SRS ECU internal drive circuit fault: Breakdown of an internal ECU transistor or drive chip causes the diagnostic circuit to incorrectly detect a short to power.
  • 5Wiring harness damage from aftermarket modifications: Fixing screws or clips pierce the airbag wiring harness insulation when retrofitting seat ventilation/heating, installing floor sound insulation, or replacing seat covers.
What To Do
  • 1
    Safety preparation: Switch the vehicle OFF, disconnect the 12V battery negative terminal, and wait at least 90 seconds to fully discharge the SRS ECU internal capacitor and prevent accidental airbag deployment.
  • 2
    Fault confirmation: Use the genuine BYD VDS diagnostic tool to read all DTCs. Check for related fault codes such as B1742-11 (short to ground) and B1742-13 (open circuit). Confirm the fault is Active, not a history fault.
  • 3
    Visual inspection: Remove the left rear C-pillar trim panel (or left rear seat side trim panel, depending on airbag installation position). Inspect the yellow airbag wiring harness connector for oxidation, water ingress, or looseness. Inspect the wiring harness for wear at the seat rails and hinges.
  • 4
    Circuit measurement: Disconnect the connectors at the SRS ECU and the airbag module. Use a multimeter to measure the harness-side connector: 1) Measure voltage at both ends of the airbag circuit (must be 0V; a B+ reading indicates a short to power); 2) Measure resistance to ground (must be infinite); 3) Measure harness continuity to confirm no open circuit.
  • 5
    Component isolation test: After verifying the wiring harness is normal, independently measure the left rear side airbag module resistance (standard value: 2.0-3.0Ω; a reading near 0Ω or infinity indicates an internal module fault). Note: Never use a standard multimeter resistance setting to directly measure a connected airbag module. The test current can trigger deployment.
  • 6
    Repair or replace: If the wiring harness is damaged, repair it with high-temperature insulating tape (Kapton tape) and re-secure the routing to prevent contact with sharp metal edges; if the airbag module has an internal short circuit, replace the left rear side airbag assembly (simultaneously replace the retaining bolts and any damaged brackets); if the SRS ECU is faulty, replace and recode the ECU.
  • 7
    System verification: Restore all connections, reconnect the battery, and use VDS to clear the fault code. Perform the SRS system self-test (indicator lamp check in Active Test). Confirm B174212 does not return and the instrument cluster airbag warning lamp turns off. Finally, perform a road test to confirm.
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM: Left rear airbag harness connector shorted due to water ingress after wading

✓
After the vehicle drove through water approximately 40 cm deep, the airbag warning light stayed on. VDS detected active fault B174212. Removing the left rear C-pillar trim revealed clear water ingress on the left rear side airbag harness connector (inside the sill trim below the C-pillar), with verdigris corrosion on the terminal surfaces. Cleaned the connector with electronic cleaner, blew it dry, and measured the harness insulation—returned to normal. Reapplied insulating silicone grease and sealed the waterproof boot. Fault resolved.
BYD DTC AI Analysis

Qin Pro petrol: Seat modification caused wiring harness damage

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After the owner installed aftermarket rear seat heating pads, the airbag warning light came on. Inspection found that a plastic clip securing the seat heating harness had crushed through the factory left rear side airbag harness during the modification (on this model, the side airbag is integrated into the seat backrest). This exposed the copper conductors, which contacted the seat metal frame (the frame is grounded, but this actually created a short to power via the body circuit). Repaired the harness by cutting out the damaged section, soldering the wires, and applying double-layer insulation. Rerouted the harness away from the seat adjustment mechanism. Fault resolved.
BYD DTC AI Analysis

Airbag module internal igniter short circuit replacement case

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The vehicle had no accident history. The airbag warning light came on suddenly while driving. VDS reported fault code B174212. Disconnected the airbag module connector and measured the harness side: no short to power. Measured the resistance directly between the airbag module terminals: 0.3 Ω (well below the normal 2–3 Ω), indicating an internal squib short circuit in the module. Replaced the left rear side airbag assembly (including inflator and airbag). Used VDS to perform the 'Replace Airbag Module' configuration procedure. After clearing the fault codes, the system returned to normal.
BYD DTC AI Analysis

Reference case: Haval H9 radar sensor short-to-power troubleshooting logic (B190112)

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Although these are different systems, refer to this circuit diagnostic logic: wait one minute after IGN ON to record the fault, remove the faulty sensor and inspect the detector surface, measure the connections and voltage at the ECU power supply pins, use the substitution method to confirm the sensor is faulty, then replace the sensor and clear the DTC. This procedure also applies to verifying B174212 using the substitution method—swap the faulty side airbag module with the right-hand module and check if the DTC transfers to confirm module failure.
Original source ↗
Other Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.
Common problems reported for Atto 3 →Atto 3 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.