AU
B164212

This DTC indicates an abnormal electrical connection between the driver-side seat belt pretensioner squib circuit and vehicle power positive (B+), causing the SRS control unit to detect a continuous high voltage (near 12V) across the pretensioner terminals — Atto 3

Safety System

This DTC indicates an abnormal electrical connection between the driver-side seat belt pretensioner squib circuit and vehicle power positive (B+), causing the SRS control unit to detect a continuous high voltage (near 12V) across the pretensioner terminals.

As a key actuator in the passive safety system, the pretensioner has a normal operating resistance of 2.0-3.0 ohms.

The SRS ECU supplies a momentary deployment current only upon receiving a collision signal.

A short to power causes the SRS ECU to immediately enter fault protection mode and disable all airbag deployment functions.

During a collision, the pretensioner fails to deploy and tighten the seat belt.

In extreme cases, the short circuit may trigger unintended pretensioner activation, severely threatening occupant safety.

This is a hard fault; once confirmed, it typically does not self-recover.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Mechanical wear of the under-seat wiring harness: Repeated movement of the driver's seat fore-and-aft adjustment mechanism rubs the pretensioner wiring harness against the seat rail and metal bracket. This friction damages the insulation, allowing the conductor to contact the power wire and create a short circuit.
  • 2Connector water ingress or corrosion: Vehicle wading, interior cleaning, or a sunroof leak causes liquid to enter the pretensioner connector under the seat (e.g., KJG series plug). Terminal oxidation produces conductive material, causing a short circuit between adjacent pins.
  • 3Pretensioner internal igniter fault: Damaged insulation on the internal pyrotechnic charge cartridge or bridge wire shorts the internal coil to the housing or power terminal, usually resulting in abnormal resistance.
  • 4Improper repair or modification: Incorrect wiring connections during accident repairs, or splicing wires to power aftermarket seat heating, ventilation, or massage equipment, mistakenly connecting the pretensioner circuit to constant power (B+).
  • 5SRS ECU internal drive circuit fault: The ECU internal pretensioner drive transistor or monitoring circuit shorted, causing continuous high voltage output to the pretensioner circuit (rule out wiring faults before confirming ECU fault).
What To Do
  • 1
    Safety Preparation: Turn the ignition switch to the OFF position and disconnect the low-voltage battery negative terminal. Wait at least 90 seconds (3 minutes for some models) to fully discharge the SRS energy storage capacitor and prevent accidental airbag deployment.
  • 2
    DTC confirmation and freeze frame analysis: Connect the diagnostic tool to read all DTCs and freeze frame data. Record the vehicle status at the time of the fault (e.g., seat position, ambient temperature). Verify if it is a current fault (Current Code).
  • 3
    Visual and physical inspection: Inspect the pretensioner connector under the driver's seat (usually located inside the outer seat trim panel or at the seat bottom) for looseness, water ingress, pin corrosion, or wiring damage. Check the wiring harness retaining clips near the seat rails for detachment.
  • 4
    Circuit insulation and continuity test: Disconnect the pretensioner connector and the SRS ECU connector. Use a multimeter to measure the resistance between the pretensioner circuit (usually the corresponding ECU terminal) and the positive power supply (B+). Resistance must be infinite (OL). Measure the resistance to ground. Resistance must also be infinite (OL). Check the insulation between the wiring harness and the seat metal components.
  • 5
    Pretensioner unit resistance measurement: Disconnect the pretensioner connector. Measure the resistance directly between the two terminals of the pretensioner unit. The standard value is 2.0-3.0 ohms (some models allow 1.5-3.5 ohms). Replace the pretensioner unit if the resistance deviates significantly or indicates a short circuit (close to 0 ohms).
  • 6
    Harness repair and isolation: If the wiring harness is damaged, repair the insulation using heat-shrink tubing or waterproof tape. Reroute the harness to keep it clear of moving seat parts, secure it to a non-moving part of the seat frame using cable ties, and leave enough slack to prevent stretching.
  • 7
    Component replacement: If diagnostics confirm an internal pretensioner short circuit (abnormal resistance and no external wiring short circuit), replace the driver seat belt pretensioner assembly (usually requires replacement with the seat belt retractor; do not disassemble or repair separately).
  • 8
    System reset and function verification: Reconnect all connectors and the battery. Use the OEM diagnostic tool to clear the fault code. Perform an SRS system self-diagnosis (typically including a circuit resistance test and crash sensor inspection) to confirm B164212 does not return. Perform a full-range fore-and-aft seat adjustment test to confirm there is no wiring harness interference.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Seat rail wear caused pretensioner wiring short circuit on BYD Yuan Plus

✓
The airbag warning light suddenly came on in a 2022 BYD Yuan Plus (same platform as the vehicle for DTC B164212). Using a VDS2000 scan tool, we retrieved DTC B164212. Removing and inspecting the driver's seat revealed that, due to frequent seat adjustments, the sharp edge of the seat rail had worn through the insulation of the pre-tensioner harness beneath the seat, causing the copper conductors to contact the rail (ground). Improper harness routing also caused the harness to chafe against the seat heating power wire, wearing through the insulation and creating a short to power. Repair: Replaced the damaged harness section, wrapped the harness with abrasion-resistant corrugated tubing, repositioned the harness mounting to clear the seat rail travel range, and recalibrated the seat position sensor, which cleared the fault.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Water-damaged vehicle: pretensioner connector corroded and shorted

✓
A 2019 BYD Qin EV displayed 'Check SRS System' on the instrument cluster after wading through water during a heavy rain. The scan tool retrieved DTC B164212 and multiple related short-circuit fault codes. Inspection found severe water ingress inside the pretensioner connector KJG05 located under the driver's seat. Terminal surface oxidation had produced verdigris, creating a low-resistance path between the power monitoring terminal and pretensioner drive terminal, causing the ECU to falsely detect a short to power. Repair procedure: Disconnected the connector, thoroughly cleaned the terminals using electronic contact cleaner, removed oxide deposits, applied specialized conductive anti-corrosion grease, replaced the waterproof seal, reinforced the connector sealing with heat shrink tubing, and cleared the fault codes. The system returned to normal.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

After accident repair, an incorrectly connected pretensioner connector caused a short circuit.

✓
A 2018 BYD Qin Pro DM logged DTC B164212 immediately upon startup after front collision repairs. The repairer had mistakenly swapped the pretensioner plug (yellow, with shorting bar) with the seat lumbar support motor plug (same colour, different pin layout) when reinstalling the driver's seat. This connected the pretensioner directly to 12V constant power, causing a short to power. Fortunately, the SRS ECU protection circuit cut off in time, preventing pretensioner deployment. Correcting the plug connections, checking the pretensioner resistance (2.3 ohms, normal), and using the diagnostic tool to run 'Crash Output Clear' and 'SRS Configuration' cleared the fault.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

Aftermarket seat ventilation installation damaged wiring, causing a short circuit

✓
A 2020 BYD E3. The airbag light came on the day after the owner installed an aftermarket seat ventilation system. We found the installer had cut into the pretensioner harness insulation to tap power. A poor connection between the splice terminal and the pretensioner wire arced, burning the insulation and causing the harness to short to the ventilation fan's constant 12V wire. Repair: Removed the aftermarket equipment. Cut out the severely damaged section of the pretensioner harness, re-soldered the wires, and sealed with heat-shrink tubing. Restored the original wiring routing. Advised the owner against modifying safety circuits.
BYD DTC AI AnalysisFrom Chinese market (translated)

Pretensioner internal squib insulation damaged

✓
A 2019 BYD E2 with no accident history developed intermittent DTC B164212. Initial wiring checks found no faults. The pretensioner's static resistance measured 2.1 ohms (normal), but when the seat was vibrated and the pretensioner housing lightly tapped, the reading swung sharply between 0.5 and 5 ohms. This fluctuation pointed to internal short circuits under vibration, likely from micro-cracks in the squib insulation or moisture inside the pyrotechnic cartridge. Replaced the driver-side seat belt retractor assembly (including pretensioner). Continuous monitoring for one week showed no recurrence of the fault.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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. Sources: [1]