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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 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.

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Cases Logged
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
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: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.