AU
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 8

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 8 indicates a high-severity SRS fault where the left rear side airbag squib circuit has an abnormally low-resistance short to battery power. This can disable the airbag system and may prevent correct deployment in a crash. Common causes include damaged wiring under the left rear seat or C-pillar trim, or an internal airbag igniter short. 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 8
  • 1Wiring harness wear under the left rear seat or inside the C-pillar trim panel: During long-term vehicle use, fore-and-aft seat 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 ignition charge or a manufacturing defect causes the ignition resistance wire to short to the housing.
  • 3Connector water ingress or terminal corrosion: Vehicle wading, vehicle washing, or poor window seals cause water ingress into the left rear airbag wiring harness connector (usually yellow), creating an electrolytic conductive path between the terminals.
  • 4SRS ECU internal drive circuit fault: Transistor or driver chip breakdown inside the ECU causes the diagnostic circuit to falsely detect a short to power.
  • 5Aftermarket modifications causing wiring harness damage: Mounting screws or clips pierce the airbag wiring harness insulation when retrofitting seat ventilation/heating, installing floor sound deadening, 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 accompanying fault codes such as B1742-11 (short to ground) and B1742-13 (open circuit). Confirm the fault is Active, not a historical 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. Check the wiring harness for wear at the seat rails and hinges.
  • 4
    Circuit measurement: Disconnect the SRS ECU and airbag module connectors. Use a multimeter to measure the harness-side connectors: 1) Measure voltage to power at both ends of the airbag circuit (should be 0V; B+ voltage indicates a harness short to power); 2) Measure resistance to ground (should be infinite); 3) Measure harness continuity to confirm no open circuit.
  • 5
    Component isolation test: Verify the wiring harness is normal, then 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 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 (replace the retaining bolts and any potentially damaged brackets simultaneously); if the SRS ECU is faulty, replace and recode the ECU.
  • 7
    System verification: Restore all connections. Reconnect the battery. Use VDS to clear the fault code. Perform the SRS system self-test (indicator light check in Active Test). Confirm B174212 does not return and the instrument cluster airbag warning light turns off. Conduct 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

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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 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.