AU
B172B

DTC B172B indicates the SRS (airbag) control unit detects an open circuit or disconnected condition in the left middle-row side airbag module (typically located inside the left B-pillar trim or on the side of the left rear seat) — Qin Plus

Safety System

DTC B172B indicates the SRS (airbag) control unit detects an open circuit or disconnected condition in the left middle-row side airbag module (typically located inside the left B-pillar trim or on the side of the left rear seat).

An abnormal resistance value in the circuit between the control unit and the airbag squib (typically infinite or outside the normal 2-3Ω range) causes the system to determine the airbag module is physically disconnected or internally open.

This fault prevents the left middle-row side airbag from deploying during a side-impact collision.

The SRS system may also enter a degraded protection mode, continuously illuminate the instrument panel airbag warning light, and restrict seat belt pretensioner function on some models.

The B172B fault code on the Qin Plus indicates an open or disconnected circuit in the left middle-row side airbag module. Severity is medium because this airbag may not deploy in a side impact and the airbag warning light may stay on. Common causes include a loose or corroded connector, backed-out pins, or a damaged SRS wiring harness. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
3
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Loose connector, backed-out pins, or poor contact at the left middle row side airbag module (commonly due to connector oxidation after vehicle wading, or failing to fully seat the connector after B-pillar trim panel removal and installation).
  • 2Airbag wiring harness open or shorted due to wear (especially the yellow SRS harness under the seat or at the B-pillar, where frequent fore/aft seat adjustment or door operation often causes fatigue breakage)
  • 3Internal open circuit in the left middle-row side airbag module (gas generator igniter tube aging or internal solder joint detachment causing abnormal resistance)
  • 4SRS control unit internal detection circuit fault (damaged control unit interface chip, falsely reporting left-side airbag open circuit)
  • 5Airbag module connector locking mechanism failure after a vehicle collision or severe vibration, causing a poor connection.
What To Do
  • 1
    Safe power-down: Turn off the ignition, disconnect the negative battery terminal, and wait at least 3 minutes to fully discharge the SRS capacitor and prevent accidental airbag deployment during repair.
  • 2
    Visual inspection: Remove the left B-pillar lower trim panel or the left rear seat side cover. Check the left middle-row side airbag module (yellow connector) for looseness, water ingress, corrosion, or backed-out pins. Clean the connector and reconnect it securely. Confirm the locking tab engages fully.
  • 3
    Circuit continuity test: Use a multimeter to measure wiring harness continuity between the airbag module connector and the SRS control unit (usually under the center console or center tunnel). Check for open circuits, short circuits, or shorts to ground, focusing on harness bend points at the B-pillar hinge and under the seat.
  • 4
    Resistance measurement: Use a dedicated airbag simulator or a multimeter (only with the system powered off and the module connector disconnected) to measure the resistance of the airbag module itself. Normal resistance is 2.0-3.0Ω. An infinite or 0Ω reading indicates an internal module fault.
  • 5
    Cross-check: Swap the left middle-row side airbag module with the right-side module (or connect a known-good simulator). Clear the fault code and power on again. Observe if the fault code follows the module to determine if the fault lies in the module or the wiring harness/control unit.
  • 6
    Control unit inspection: If the wiring harness and module are normal, check the SRS control unit connector pins for oxidation or deformation. If necessary, measure the control unit internal interface circuit to confirm an internal control unit fault.
  • 7
    System reset verification: After repair, reconnect all components and the battery. Use VDS or a dedicated diagnostic tool to clear the fault code. Perform the SRS system self-check (usually requires 3 ignition cycles). Confirm the instrument panel warning light turns off and the fault code does not reappear.
Real-World Cases
BYD DTC AI Analysis

BYD Tang B172B fault: Oxidised left middle row side airbag connector caused open circuit

✓
Symptoms: 2021 BYD Tang, airbag warning light stays on. DTC B172B stored (left second-row side airbag module disconnected). No collision history. Diagnosis: Inspected the airbag connector below the left B-pillar. Found green oxide inside with poor pin contact. Wiring harness continuity normal. Airbag module resistance 2.3Ω (normal). Repair: Cleaned connector pins with electronic cleaner, applied conductive grease, and reconnected. Cleared fault code; no recurrence. Analysis: Vehicle previously went through water. Moisture entered the B-pillar connector, causing oxidized high-resistance contact.
Original source ↗
BYD DTC AI Analysis

BYD Song MAX seat wiring harness chafing caused B172B

✓
Symptoms: 2019 Song MAX, airbag warning light illuminated intermittently while driving, diagnostic tool showed intermittent B172B fault. Diagnosis: Inspection found the SRS wiring harness beneath the left second-row seat interfering with the seat rail, with worn insulation causing the internal wires to intermittently open circuit. Repair: Repaired the damaged harness, wrapped it with corrugated tubing, and re-secured the harness routing to ensure safe clearance from the seat mechanism. Fault cleared.
Original source ↗
BYD DTC AI Analysis

BYD Qin Pro Left Second-Row Side Airbag Module Internal Fault Replacement Case

✓
Symptoms: SRS warning light stays on after starting the BYD Qin Pro. Fault code B172B will not clear. Diagnosis: Measured infinite resistance (open circuit) across left middle row side airbag module. Wiring harness continuity and connector contacts were good. Diagnosed an open circuit in the airbag module's gas generator igniter. Resolution: Replaced left middle row side airbag module assembly (transport safety precautions observed for new part). Used diagnostic scan tool to configure and match the system, then ran airbag self-test. Fault resolved.
Original source ↗
Other Qin Plus 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.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.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus 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.