AU
B164A

DTC B164A indicates the SRS (Supplemental Restraint System) electronic control unit detects abnormal resistance in the deployment circuit of the front passenger seat belt pretensioner (or driver-side airbag, depending on vehicle configuration), identifying an open circuit (disconnected) — Atto 3

Safety System

DTC B164A indicates the SRS (Supplemental Restraint System) electronic control unit detects abnormal resistance in the deployment circuit of the front passenger seat belt pretensioner (or driver-side airbag, depending on vehicle configuration), identifying an open circuit (disconnected).

The SRS system continuously monitors the circuit resistance of the airbag/pretensioner gas generator (normal value approximately 2-3 Ω, including the series diagnostic resistor) to ensure reliable ignition during a collision.

The ECU triggers DTC B164A when it detects infinite resistance (>6 Ω) or a communication interruption.

This fault prevents the deployment circuit from firing correctly during a collision, illuminates the airbag warning light continuously, and forces the system into fail-safe mode.

On some BYD models, DTC B164A specifically indicates a driver airbag (DAB) circuit fault.

The underlying issue remains the same type of abnormal connection in the deployment circuit.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Broken spiral cable or burnt contacts inside the clock spring (airbag spiral cable/Clock Spring), causing an intermittent open circuit during steering wheel rotation.
  • 2Loose connector, backed-out pins, or oxidized/corroded terminals under the front passenger seat or at the B-pillar seat belt pretensioner, or connector position assurance (CPA) lock not fully engaged, causing an intermittent connection.
  • 3Airbag module or pretensioner wiring harness connector not fully seated after accident repairs, or pulling during repairs deformed the pins.
  • 4The seat slide rail, steering column tube, or body frame pinches and chafes the wiring harness, causing broken conductor cores or intermittent short circuits.
  • 5SRS control module internal monitoring circuit fault, poor solder joint, or internal open circuit in the airbag/pretensioner gas generator.
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal and wait at least 90 seconds (some models require 2 minutes) to fully discharge the SRS capacitor and prevent accidental deployment.
  • 2
    Diagnostic confirmation: Use the BYD VDS2000/VDS diagnostic tool to read the fault code and check the freeze frame data. Determine whether the fault is historical or current, and confirm the specific faulty component (front passenger pretensioner or driver airbag).
  • 3
    Visual inspection: Check the seat belt pretensioner connector (usually yellow) under the front passenger seat (or B-pillar) for a secure connection, a broken locking tab, green oxidation on the terminals, or backed-out terminals.
  • 4
    Resistance measurement: Disconnect the airbag/pretensioner connector. Use a digital multimeter to measure the resistance between the two terminals of the deployment circuit (normal: 2-3 Ω). Measure the resistance from the wiring harness side to ground and to power (should be infinite to rule out a short circuit).
  • 5
    Circuit continuity test: Use a multimeter to measure wiring harness continuity from the SRS ECU to the connector. Inspect the moving wiring harnesses near the seat rails and steering column for breaks.
  • 6
    Component isolation test: If the pretensioner body resistance is infinite, replace the seat belt pretensioner assembly. If the circuit involves the clock spring, measure continuity at different steering angles.
  • 7
    Repair and verification: Repair or replace the damaged wiring harness/connector. Reconnect all connectors and verify the locking tabs click into place. Connect the battery. Clear the fault code. Perform the SRS system self-check (ignition switch ON; warning light illuminates for 6 seconds then turns off to indicate normal operation).
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Song Pro airbag system fault

✓
Symptom: Airbag warning light on dashboard stays on continuously. Diagnosis: Used VDS to read fault code B164A, indicating open circuit in driver's side airbag module. Removed and inspected the clock spring; found internal spiral cable broken. Measured resistance 8.5Ω (exceeds spec). Solution: Replaced clock spring, reconnected wiring harness, cleared fault codes. System returned to normal.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Tang DM seat airbag communication fault

✓
Symptoms: While driving, the instrument cluster intermittently displayed "Check Airbag System", especially on rough roads. Diagnosis: Retrieved DTC B164A (Driver Seat Side Airbag Module Communication Fault). Inspection found the connector under the driver’s seat loose with oxidised pins. The seat track mounting bolts crushed the harness, causing an intermittent short in the CAN communication wire (resistance fluctuated 5–25Ω). Resolution: Repaired the damaged harness, rerouted it clear of the seat’s range of motion, and cleaned and secured the connector. Fault cleared.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin Plus airbag control module fault

✓
Symptoms: The airbag warning light turned on suddenly after servicing, with no history of collisions or water damage. Diagnosis: VDS2000 retrieved DTC B164A (Driver airbag first stage deployment loop resistance out of range). Found that the connector was loose due to strain on the wiring harness during previous dashboard trim panel removal; resistance was 5.2Ω, slightly high. Resistance returned to normal after reseating the connector, but the fault code would not clear. Resolution: Performed the airbag control module 'Configuration and Setup' function, recalibrated the deployment loop parameters, cleared the DTC, and restored normal operation.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Han EV steering wheel airbag circuit fault

✓
Symptoms: Airbag warning light came on for no apparent reason three months from new; returned after a power reset. Diagnosis: DTC B164A (Driver Airbag Module DAB circuit fault). Inspection found the clock spring off‑centre; at full steering lock, internal contacts became intermittent and resistance read infinite. Fix: Replaced the clock spring assembly with genuine part SKE-3636100, centred it strictly as per the workshop manual, and performed steering angle sensor calibration. Resolved.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Yuan Pro airbag fault after collision

✓
Symptoms: After a minor frontal collision at 15 km/h, the airbag did not deploy. After repairs, the airbag warning light stayed on. Diagnosis: Read DTC B164A (driver side airbag deployment loop performance fault). Measured resistance at 0.8 Ω (too low). The collision shifted the steering wheel frame, compressing the airbag harness and causing a short circuit. The previous repair had not inspected this harness. Resolution: Repaired the steering wheel frame bracket, replaced the damaged airbag harness, and adjusted the steering wheel position to centre it. Resistance returned to 2.4 Ω and the system operated normally.
Original source ↗
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]