AU
B164C-00

This DTC indicates an abnormal short circuit between the front passenger seat belt pretensioner ignition circuit and the vehicle power supply (+B, typically the positive terminal of the 12V battery) — Atto 3

Safety System

This DTC indicates an abnormal short circuit between the front passenger seat belt pretensioner ignition circuit and the vehicle power supply (+B, typically the positive terminal of the 12V battery).

The pretensioner is a pyrotechnic device.

During a collision, the SRS control unit sends an ignition signal to trigger the internal gas generator and rapidly tighten the seat belt.

A short to power in the pretensioner circuit indicates damaged wiring insulation or internal connector bridging, applying a continuous high potential across the pretensioner terminals.

This condition forces the SRS system into fail-safe mode, disabling the front passenger airbag and pretensioner functions.

Extreme cases risk unintended pretensioner deployment or complete failure, posing a severe safety hazard.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Chafed or crushed wiring harness under the front passenger seat: Seat fore-and-aft adjustment or passenger foot movement damages the pretensioner wiring harness insulation (usually located near the seat rail), causing it to contact a power wire (such as the seat heater or seat adjustment motor power wire) and short circuit.
  • 2Water ingress into the B-pillar or sill wiring harness connector: Vehicle wading or poor sealing corrodes the internal terminals of the pretensioner connector (usually located behind the B-pillar trim panel or under the seat), creating a conductive path and causing a short to power.
  • 3Pretensioner internal fault: Insulation failure of the igniter (squib) inside the pretensioner assembly causes a short circuit between the ignition terminal and the housing or power terminal. Abnormal resistance (below 1.5Ω or above the normal range) usually accompanies this condition.
  • 4SRS control unit internal drive circuit fault: Breakdown of the internal ignition drive transistor or a shorted filter capacitor causes the pretensioner terminal to continuously output a high level.
  • 5Non-professional modifications: Improper installation of seat ventilation, heating, or ambient lighting pierces the pretensioner wiring harness, or incorrectly connects the pretensioner circuit in parallel with a constant power circuit.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds for the SRS capacitor to fully discharge and prevent accidental airbag deployment.
  • 2
    Fault Confirmation: Use the BYD dedicated diagnostic tool (VDS or ED400) to read fault codes. Confirm B164C-00 is a current fault (Active), record freeze frame data, and check for accompanying B164B (open circuit) or B164D (short to ground) fault codes.
  • 3
    Visual inspection: Remove the front passenger seat (if applicable) and the lower B-pillar trim. Inspect the pretensioner connector (usually a yellow 2-pin plug) for signs of water ingress, burn marks, bent pins, or corrosion. Inspect the wiring harness under the seat for wear, damaged insulation, or interference with the seat track.
  • 4
    Circuit measurement: Disconnect the SRS control unit and pretensioner connectors. Use a multimeter to measure the voltage at the pretensioner harness side (should be <1V), measure the pretensioner resistance (standard value: 2.0-3.0Ω, varies slightly by model), and check the harness for a short to power (resistance between the pretensioner connector terminal and the vehicle power supply should be infinite).
  • 5
    Wiring harness repair: If the wiring harness is damaged, wrap it with high-temperature insulating tape (≥125°C) or replace the wiring harness assembly; if the connector has water ingress, clean it with electronic contact cleaner and blow dry, and replace the connector if necessary; fully seat the wiring harness retaining clips to prevent interference with moving parts.
  • 6
    Component replacement: If the measured pretensioner resistance is abnormal (<1Ω or >5Ω) or internally shorted to power, replace the front passenger seat belt pretensioner assembly. (Note: The pretensioner is a single-use component. Replace it if dropped or subjected to impact.)
  • 7
    System reset: Reconnect all connectors, restore battery power, clear the fault code using the diagnostic tool, and perform the SRS system self-check (typically requires turning the ignition switch to ON and observing if the SRS warning lamp turns off). Finally, perform a dynamic test (simulate a crash signal using special equipment; do not perform an actual vehicle crash test).
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Seat rail wear caused pretensioner short circuit in Qin EV450

✓
A 2018 Qin EV450 with 32,000 km had the SRS warning light staying on. Scanning showed DTC B164C-00. The wiring harness retaining clip under the passenger seat had come loose, letting the harness chafe against the metal edge of the seat track. The insulation wore through and the exposed copper wires contacted the seat heater constant +12V feed. Repaired the two damaged wires (pretensioner trigger and return), re-secured the harness, and added corrugated conduit for protection. Fault resolved.
BYD DTC AI AnalysisFrom Chinese market (translated)

B-Pillar Connector Corrosion Case: Water-Wading Vehicle

✓
2017 BYD Qin 100. Dashboard displayed airbag fault after driving through floodwater during a typhoon. Diagnostic scan found codes B164C-00 and B1650-00 (driver's side equivalent). Removed the passenger side B-pillar trim and found visible water staining and green corrosion inside the yellow pretensioner connector. Degraded insulation resistance between terminals caused a short to power. Cleaned the connector with anhydrous alcohol, dried it, applied conductive protective grease, and replaced the waterproof seal. Fault resolved. Check the sunroof drain tubes and door seals.
BYD DTC AI AnalysisFrom Chinese market (translated)

Internal short in pretensioner after accident repair

✓
After the Qin EV300’s front collision repair, the SRS light stayed on. The front passenger airbag had been replaced after the impact, but the seatbelt was not. Diagnostics found DTC B164C-00. The pretensioner measured 0.8 Ω (too low) and was shorted to power. Disassembly revealed that the collision impact caused a breakdown short circuit in the semiconductor bridge (SBB) inside the pretensioner’s igniter. Replacing the front passenger seatbelt assembly (including pretensioner) cleared the fault codes and restored normal operation.
BYD DTC AI AnalysisFrom Chinese market (translated)

Aftermarket heated seat modification caused a fault.

✓
The owner installed an aftermarket ventilation and heating pad on the passenger seat. During installation, they overtightened the cable ties securing the wiring, which cut into and damaged the factory pretensioner wiring harness. They also incorrectly tapped the heating pad into the pretensioner circuit for power. This triggered DTC B164C-00 and heating function faults. Repair involved removing the modified wiring, repairing the original harness (two damaged wires), restoring the factory circuit layout, and advising the owner that airbag system wiring must never be modified.
BYD DTC AI AnalysisFrom Chinese market (translated)

SRS control unit internal fault misdiagnosis case

✓
A BYD Qin 80 repeatedly set DTC B164C-00. Previous repairs replaced the pretensioner and wiring harness, but the fault recurred intermittently. The root cause turned out to be a thermally unstable firing driver chip (typically a high-power MOSFET) inside the SRS control unit. After a period of operation, the chip broke down and shorted to power. Replacing the SRS control unit (under the center console or inside the dashboard) and performing vehicle configuration programming permanently fixed 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]