AU
B163C-00

This DTC indicates the airbag control unit (SRS ECU) detects the resistance of the front passenger side airbag (typically the seat side airbag or door side airbag) ignition circuit exceeds the calibrated threshold (normal value typically 2 — Atto 3

Safety System

This DTC indicates the airbag control unit (SRS ECU) detects the resistance of the front passenger side airbag (typically the seat side airbag or door side airbag) ignition circuit exceeds the calibrated threshold (normal value typically 2.0-3.0Ω, fault threshold typically >4.0Ω).

This indicates a high-resistance condition in the ignition circuit, classified as a soft fault (precursor to an intermittent open circuit).

Poor connector contact, a partially broken wiring harness, increased contact resistance in the clock spring (spiral cable), or aging of the internal resistance wire in the airbag module can cause this condition.

This fault causes the SRS system to mark the airbag as unreliable.

During a collision, the airbag may fail to deploy normally or experience a deployment delay.

The system illuminates the airbag warning lamp and disables the airbag function, severely compromising passive safety performance.

4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Oxidation, loose connection, or water ingress at the airbag connector (yellow plug) under the front passenger seat, causing increased contact resistance (common after vehicle wading or prolonged exposure to damp environments).
  • 2Wear, poor contact, or partial open circuit of the internal slip ring in the spiral cable (clock spring), causing unstable signal transmission resistance.
  • 3Aging, cold solder joints, or partial breakage of the internal igniter resistance wire in the side airbag module, causing increased internal resistance.
  • 4Frequent seat position adjustment causes copper wire fatigue fractures in the seat wiring harness (not completely broken, only a few copper strands remain connected), forming a high-resistance circuit.
  • 5Airbag ECU internal monitoring circuit sampling resistor drift or software false alarm (less common; confirm after ruling out external wiring).
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal and wait at least 3 minutes to fully discharge the SRS system and prevent accidental airbag deployment.
  • 2
    Data reading: Use the BYD VDS2000/VDS2100 diagnostic tool to read the detailed data stream. Record the current resistance value, the ambient temperature when the historical fault occurred, and the vehicle status.
  • 3
    Connector check: Inspect the yellow airbag connector under the front passenger seat (usually near the seat rail) for looseness, water ingress, or oxidation. Clean the terminals, apply a conductive protective agent, and measure the resistance across both ends of the connector.
  • 4
    Unit measurement: Remove the front passenger seat side trim panel. Disconnect the airbag module connector. Use a high-precision multimeter to directly measure the airbag unit resistance (standard value: 2.0 ± 0.3 Ω; values exceeding 3.5 Ω are abnormal).
  • 5
    Harness inspection: Check the seat-to-body harness conduit for wear, crushing, or partially broken copper strands due to seat movement. Focus on harness bends in the seat fore-aft adjustment area.
  • 6
    Clock spring inspection: If involving the steering wheel or B-pillar connection (some models connect the side airbag through the B-pillar), check the continuity and resistance stability of the spiral cable (clock spring).
  • 7
    Fault Repair: If inspection reveals a high-resistance point, repair or replace the wiring harness. If the airbag unit resistance is abnormal, replace it with a genuine side airbag module. If all components are normal, check the SRS ECU.
  • 8
    System reset: Reconnect all connectors (listen for the locking 'click'), reinstall the components, and connect the battery. Use the diagnostic tool to clear the fault code and perform a system self-check. Confirm the resistance value returns to the normal range.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin EV450 seat connector oxidation caused high resistance

✓
After driving through water, the airbag warning light stayed on. Retrieved DTC B163C-00. Checked the airbag connector under the front passenger seat and found obvious oxidation and white corrosion on the terminals. Cleaned the terminals with electronic cleaner, applied conductive grease and reconnected. Resistance dropped from 5.2Ω to 2.1Ω. Fault cleared. Check under the carpet for any remaining water to prevent recurrence.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin 100 seat wiring harness fatigue fracture case

✓
The airbag warning light came on intermittently while driving, and DTC B163C-00 appeared intermittently. Inspection found the wiring harness under the passenger seat had fractured at the conduit exit from repeated seat adjustment, with 90% of the internal copper strands broken and only a few still connected. Measured resistance jumped between 2.8 and 6.5 ohms. We cut out the damaged section, re-soldered and extended the harness with thicker wire, and rerouted it to prevent flexing. This completely resolved the fault.
BYD DTC AI AnalysisFrom Chinese market (translated)

Clock spring internal contact fault

✓
Airbag warning light flickers intermittently when turning the steering wheel, with DTC B163C-00 present. Because part of the passenger side airbag harness on this model is routed through the B-pillar or clock spring, disassembly and inspection revealed wear on the slip rings inside the clock spring, causing resistance to vary between 2.0–8.0 Ω as the steering wheel turns. Replaced with a genuine clock spring. Resistance stabilised at 2.0 Ω and the fault has not recurred.
BYD DTC AI AnalysisFrom Chinese market (translated)

Side airbag module internal resistance wire aging

✓
After 5 years of service, a B163C-00 fault appeared. External wiring harness and connectors checked normal. Directly measured resistance at the airbag module connector: 4.8Ω (high). Replaced the passenger side airbag module (requires removing the leather seat cover), restoring normal resistance. The internal igniter resistance wire aged from prolonged seat compression and temperature changes, increasing its resistance.
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]