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 8

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 8
  • 1Mechanical wear of under-seat wiring harness: Long-term movement of the driver's seat fore-and-aft adjustment mechanism rubs the pretensioner wiring harness against the seat rail and metal bracket. Damaged insulation allows the core wire to contact the power wire, causing a short circuit.
  • 2Connector water ingress or corrosion: Vehicle wading, interior cleaning, or a sunroof leak allows liquid to enter the under-seat pretensioner connector (such as the KJG series plug). Terminal oxidation produces conductive material, causing a short circuit between adjacent pins.
  • 3Pretensioner internal squib fault: Damaged insulation on the internal initiator or bridge wire shorts the internal coil to the housing or power terminal, usually accompanied by abnormal resistance.
  • 4Improper repair or modification: Incorrect wiring connections during accident repairs, or splicing wires to power aftermarket seat heating/ventilation/massage equipment, mistakenly connecting the pretensioner circuit to constant power (B+).
  • 5SRS ECU internal drive circuit fault: ECU internal pretensioner drive transistor or monitoring circuit breakdown causes 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 OFF, disconnect the low-voltage battery negative terminal, and 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 the complete fault codes and freeze frame data. Record the vehicle status when the fault occurred (such as seat position and ambient temperature). Confirm whether 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 bottom) for looseness, water ingress, corroded pins, or wiring harness damage; inspect 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 at the corresponding ECU terminal) and the positive power supply (B+). The resistance must be infinite (OL). Measure the resistance to ground; the value 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 and measure the resistance directly between the two pins of the pretensioner unit. The standard value is 2.0-3.0 ohms (some models allow 1.5-3.5 ohms). Replace the pretensioner if the reading deviates excessively or indicates a short circuit (close to 0 ohms).
  • 6
    Harness repair and isolation: If the wiring harness is damaged, repair the insulation with heat-shrink tubing or waterproof tape. Reroute the harness to keep it clear of moving seat parts. Secure the harness to non-moving parts of the seat frame with cable ties, leaving sufficient slack to prevent stretching.
  • 7
    Component replacement: If testing confirms an internal pretensioner short circuit (abnormal resistance and no external wiring short circuit), replace the driver seat belt pretensioner assembly (usually requires replacing the seat belt retractor as well; do not disassemble for separate repair).
  • 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 (usually including circuit resistance tests and crash sensor checks) to verify B164212 does not return. Perform a full fore-and-aft seat adjustment test to verify 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 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: 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]