AU
B2A4E13

DTC B2A4E13 indicates an open control circuit fault in the left front (driver side) seat belt pretensioner — Atto 3

Thermal Management System

DTC B2A4E13 indicates an open control circuit fault in the left front (driver side) seat belt pretensioner.

It belongs to the body safety system (SRS), not the thermal management system.

DTC structure breakdown: 'B' represents the Body system, '2A4E' designates the left front seat belt pretensioner control circuit, and '13' indicates an open circuit.

The Airbag Control Unit (ACU) triggers this fault upon detecting abnormal resistance (open circuit or excessive resistance) in the pretensioner circuit, which prevents the formation of an effective monitoring circuit.

This fault continuously illuminates the instrument cluster SRS warning light and forces the airbag system into a degraded mode.

In extreme cases, it prevents the pretensioner from deploying during a collision, posing a severe safety risk.

Note: Unofficial sources sometimes incorrectly label this code as a high-voltage line pressure sensor fault; it strictly indicates a seat belt pretensioner circuit fault.

The B2A4E13 fault code on the Atto 3 indicates an open circuit in the left front driver-side seat belt pretensioner control circuit. This is a high-severity SRS safety fault that can keep the warning light on and may stop the pretensioner working in a crash. Common causes include a loose or corroded under-seat connector or damaged wiring near the seat rail. 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
  • 1Left front seat belt pretensioner connector under the seat loose, not fully locked, or terminals oxidized/corroded, causing excessive contact resistance or open circuit.
  • 2Repeated bending during fore-and-aft seat movement breaks internal wires in the harness transition area between the vehicle floor and the seat (especially near the seat slide rail).
  • 3Vehicle wading or damp environments causing water ingress and oxidation at the pretensioner connector, or a damaged wiring harness sleeve causing terminal corrosion.
  • 4Open circuit in the seat belt pretensioner internal resistance wire (normal resistance: 2-5 Ω; reads infinity when faulty).
  • 5Airbag Control Unit (ACU) internal monitoring circuit fault, or connector pins backed out or deformed
What To Do
  • 1
    Safety preparation: Switch the vehicle to OFF, disconnect the 12V battery negative terminal, and wait at least 90 seconds to fully discharge the airbag system and prevent accidental deployment.
  • 2
    Visual inspection: Remove the left front seat (leave the wiring harness connected). Verify the yellow plug (pretensioner connector) under the seat is fully locked. Inspect for signs of water ingress, oxidation, or burn marks.
  • 3
    Resistance measurement: Use a multimeter to measure the resistance between the pretensioner connector terminals. The standard value is 2-5 Ω. If the reading is infinite or greater than 10 Ω, the pretensioner body or wiring has an open circuit.
  • 4
    Wiring harness inspection: Inspect the wiring harness transition area between the vehicle floor and the seat, especially at the seat slide rail bend. Peel back the protective sleeve and inspect the wires for wear or breakage. Check for missing wiring harness retaining clips that cause harness movement.
  • 5
    Continuity test: Disconnect the ACU connector. Measure the wiring continuity from the pretensioner to the corresponding ACU pin. Verify there is no open circuit or poor connection.
  • 6
    Component replacement: If the wiring harness is damaged, repair it or replace the seat wiring harness assembly. If the pretensioner body resistance is abnormal, replace the pretensioner. (Note: The pretensioner is an explosive device. Do not use brute force during removal.)
  • 7
    System reset: Reconnect all connectors and confirm they lock. Connect the battery. Clear fault codes using the BYD VDS or ED-400 diagnostic tool. Perform an SRS system self-check. Confirm the warning light turns off and no current fault codes exist.
Real-World Cases
BYD DTC AI Analysis

Worn seat rail wiring harness caused intermittent open circuit on Song Pro DM-i

✓
2019 Song Pro DM-i. Instrument cluster intermittently displayed 'SRS System Fault'. Retrieved DTC B2A4E13. Found the wiring harness beneath the left front seat had chafed at the seat rail from repeated fore-aft movement, wearing through the insulation. The yellow/black wire inside was nearly severed, causing intermittent poor contact. Replaced the seat wiring harness assembly, rerouted and secured it, added anti-chafe sleeving and retaining clips to prevent strain during seat movement. Cleared the DTC and monitored for one week with no recurrence.
Original source ↗
BYD DTC AI Analysis

New Qin L DM-i pretensioner plug improperly installed.

✓
After delivery of a new 2024 Qin L DM-i, the instrument cluster intermittently displayed an airbag fault. DTC B2A4E13 cleared but returned repeatedly. Removing the left front seat revealed the seatbelt pretensioner connector was not fully locked (production line assembly defect); the missing wiring harness retaining clip allowed the connector to vibrate while driving, causing poor contact. Solution: Reconnected the connector and confirmed positive locking, installed the missing wiring harness retaining clip, and secured the harness routing with cable ties.
Original source ↗
BYD DTC AI Analysis

Sudden airbag warning on Song DM after driving on rough roads

✓
A 2019 BYD Song DM owner reported the dashboard suddenly displayed an airbag fault after driving over a bumpy road. The dealership's initial inspection found no issues. The owner used a diagnostic scanner to retrieve code B2A4E13, then reproduced the fault by wiggling the seat wiring harness. Inspection revealed multiple terminals inside the connector between the floor pan and seat (the large plug beneath the seat) had loose connections, with the yellow/black pretensioner control wire terminal almost completely backed out. Fix: Removed the terminals using a special terminal removal tool, re-crimped them, applied conductive anti-corrosion grease, and secured all seat-related connectors.
Original source ↗
BYD DTC AI Analysis

Multiple models: Oxidized pretensioner connector after water wading

✓
Applies to Song, Qin, Han and related model ranges. DTC B2A4E13 present with related codes including B1890. Vehicle has water wading history. Diagnosis: Pretensioner connector showed obvious water ingress and oxidation; resistance readings unstable. Repair: Clean connector terminals and apply conductive paste. Replace connector if oxidation is severe. Check harness boot seal and replace seat harness assembly if necessary. If water entered the pretensioner body, replace pretensioner assembly and check ACU.
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.