AU
B2A2511

DTC B2A2511 indicates a circuit fault in the left front seat belt pretensioner (Driver Seat Belt Pretensioner), specifically a short to ground or an open circuit — Atto 3

Thermal Management System

DTC B2A2511 indicates a circuit fault in the left front seat belt pretensioner (Driver Seat Belt Pretensioner), specifically a short to ground or an open circuit.

The Airbag Control Module (ACM) sets this fault code when it detects abnormal resistance in the left front pretensioner circuit (standard value: 2-3 Ω; fault condition: short circuit at <1.0 Ω, or open circuit at >4.0 Ω/infinite resistance).

This fault forces the airbag system into fail-safe mode and continuously illuminates the instrument cluster airbag warning light.

In a collision, the pretensioner may fail to deploy.

This severe fault compromises driving safety.

Note: Some online sources incorrectly identify this code as the evaporator temperature sensor; it strictly applies to the seat belt pretensioner system.

The B2A2511 fault code on the Atto 3 indicates a high-severity fault in the left front driver seat belt pretensioner circuit, caused by a short to ground or open circuit. Common causes include under-seat wiring being pinched by the seat rail, or loose, corroded, or high-resistance connector terminals. The airbag warning light stays on and the pretensioner may not deploy in a crash. Visit an authorised dealer for inspection and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Improper under-seat wiring harness routing causes the seat slide rail to pinch and wear the harness, resulting in a short to ground or open circuit.
  • 2G09 or GJK mating connector terminals backed out, oxidized, corroded, or excessive contact resistance
  • 3Seat belt pretensioner assembly internal short circuit or open circuit (e.g., pretensioner deployed in a collision but not replaced)
  • 4Airbag Control Module (ACM) internal diagnostic circuit fault or software false detection
  • 5Water ingress or a damp environment corrodes the under-seat wiring harness connector, causing an intermittent short circuit.
What To Do
  • 1
    Use the VDS2000/VDS3100 diagnostic tool to read the fault code, confirm whether B2A2511 is an Active or History code, and record the freeze frame data.
  • 2
    Disconnect the 12V battery negative terminal and wait 3 minutes for the capacitor to discharge. Inspect the pretensioner wiring harness under the left front seat for wear, damaged insulation, water ingress, or pinching by the seat slide rail.
  • 3
    Disconnect the pretensioner connector. Use a multimeter to measure the resistance of the pretensioner body (standard value: 2.0-3.0 Ω). If the resistance is 0 or infinite, replace the pretensioner assembly.
  • 4
    Inspect the G09 (floor harness side) and GJK (seat harness side) connectors. Check pins 14 and 15 for push-out or oxidation. Measure the harness-side resistance to ground and continuity to power, and locate the short circuit.
  • 5
    If the wiring harness is damaged, repair it with waterproof tape or replace the wiring harness assembly. If a terminal has backed out of the connector, recrimp the terminal and apply conductive grease. Adjust the wiring harness securing position to prevent interference with moving parts.
  • 6
    Restore all connections, tighten to the specified torque, reconnect the battery, clear the fault code, perform an airbag system self-test (Active Test), and confirm the fault does not recur.
Real-World Cases
BYD DTC AI Analysis

Seat rail pinched wiring harness causing open circuit on BYD Qin EV

✓
Airbag warning light illuminated while driving a 2018 BYD Qin EV. VDS read B2A2511. Inspection found the seat rail had crushed and severed the wiring harness beneath the left front seat. Pretensioner resistance measured infinite. Replaced floor wiring harness assembly, rerouted wiring, and secured with dedicated clips to prevent seat rail interference. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Song DM collision: pretensioners deployed but not replaced

✓
2017 BYD Song DM airbag warning light stayed on after accident repairs, storing DTC B2A2511. Inspection found the left front seatbelt pretensioner had deployed (measured resistance 0.8Ω) and crash data had locked the airbag control module. Replaced the left front seatbelt pretensioner with a new pyrotechnic unit and the airbag control module, then performed programming and matching. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Tang: Oxidised connector causing intermittent fault

✓
Intermittent airbag warning light on a 2015 BYD Tang, stored DTC B2A2511. Found GJK connector pin 14 oxidised when the fault occurred on cold start, with contact resistance fluctuating between 0.5 and 5 ohms. Cleaned the pin, applied conductive grease, reseated the connector and secured it with cable ties. Monitored for one week with no recurrence.
Original source ↗
BYD DTC AI Analysis

BYD e5 pretensioner wiring harness pin backed out, communication interrupted

✓
2016 BYD e5 taxi. Airbag warning light illuminated with DTC B2A2511 stored; pretensioner resistance measured 2.5Ω (normal). Found pins 14 and 15 of the G09 floor harness connector backed out, interrupting communication between the ACM and pretensioner. Repaired backed-out terminals by re-crimping and reinstalling. Recommended manufacturer improve connector design.
Original source ↗
BYD DTC AI Analysis

BYD Yuan EV wiring harness insulation damage, short to ground

✓
2018 BYD Yuan EV360 logged DTC B2A2511 (short to ground). Disconnected the connector and measured continuity between the harness side and body. Found the wiring harness insulation worn through under the seat and shorting to ground. Repaired the damage with waterproof tape and adjusted the harness position to ensure safe clearance from the body.
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.