AU
B163A

This fault code indicates the Supplemental Restraint System (SRS) detects a 0Ω resistance in the front passenger side airbag firing circuit (typically located in the seat side or B-pillar/curtain) — Atto 3

Safety System

This fault code indicates the Supplemental Restraint System (SRS) detects a 0Ω resistance in the front passenger side airbag firing circuit (typically located in the seat side or B-pillar/curtain).

Normal airbag igniter resistance is 1.6-2.4Ω.

A 0Ω resistance indicates a low-impedance short circuit.

Possible causes include a wiring harness short to ground, shorted connector pins, an internal short in the airbag inflator (igniter), or a faulty internal monitoring circuit in the SRS control unit (ACU).

The ECU disables this airbag circuit to prevent accidental deployment.

The airbag will fail to deploy during a side impact, severely compromising occupant protection.

Some early repair data or specific vehicle models define B163A as an anti-theft system communication fault.

Always reference the current vehicle repair manual for actual diagnosis.

4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Front passenger airbag wiring harness chafed or insulation damaged, causing a short to ground (commonly at the seat track, B-pillar trim panel, or floor wiring harness pass-through)
  • 2Water ingress, oxidation, or bent and touching pins at the under-seat airbag connector (usually located on the inner side of the seat rail or at the seat base), causing a short circuit.
  • 3Internal short circuit in airbag gas generator (igniter) causing resistance to drop abnormally to 0 Ω (replace airbag assembly).
  • 4Internal fault in the SRS control module (ACU) drive/monitoring circuit causing a false detection (actual circuit is normal but falsely reports a short circuit).
  • 5Damage to the wiring harness insulation during vehicle modifications (such as installing seat heaters, ventilation systems, or full-coverage seat covers), or a fixing screw piercing the wiring harness.
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal and wait at least 90 seconds to fully discharge the SRS capacitor and prevent accidental airbag deployment and personal injury.
  • 2
    Fault confirmation: Connect the VDS or X431 diagnostic tool to read the DTC. Confirm B163A is a Current fault rather than a History fault. Record the environmental conditions in the freeze frame data.
  • 3
    Visual inspection: Inspect the airbag wiring harness connectors under the front passenger seat, inside the B-pillar trim panel, and at the door sill for looseness, water ingress, corrosion, or obvious physical damage. Focus on the wiring harness sleeve at the seat slide rail.
  • 4
    Isolation diagnosis: Disconnect the front passenger airbag connector (use a shorting clip to protect the wiring harness side). Connect a special airbag load simulator (2Ω dummy load) to the SRS ECU side and read the resistance. If the resistance returns to normal, the fault is in the airbag module or wiring harness; if it remains at 0Ω, the fault is in the wiring harness or ECU.
  • 5
    Wiring harness inspection: Measure the resistance between the two airbag circuit wires and body ground (should be >1MΩ). Measure continuity between both ends of the wiring harness (should be <1Ω). Check for shorts to ground or power. Use an oscilloscope to check for line interference if necessary.
  • 6
    Component inspection: If the wiring harness is normal, use the dedicated airbag tester to measure the airbag inflator resistance (must be 1.6-2.4Ω; 0Ω indicates an internal short circuit requiring airbag assembly replacement. Never measure directly with a multimeter).
  • 7
    Repair/Replace: Repair the damaged wiring harness (solder and insulate with heat-shrink tubing). Replace damaged connectors (must use OEM waterproof plugs). Replace the airbag module if internally shorted. Verify all plugs clip fully into position with an audible click.
  • 8
    System verification: Reconnect the battery, clear the fault code, and turn the ignition switch to the ON position. Observe whether the airbag warning light turns off within the specified time (turning off after 6 seconds usually indicates a successful system self-check). Perform a road test to confirm.
  • 9
    Final check: Use the diagnostic tool to perform the SRS system self-test and configuration check. Confirm B163A no longer appears, verify normal operation of related functions, and complete the repair record.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Tang DM immobiliser system communication fault causing no-start condition

✓
Symptoms: Vehicle failed to start. Start button had no response, dashboard displayed "Check Powertrain" warning, warning light on. DTC B163A was stored (immobiliser authentication failure/communication error). Diagnosis: Connected scan tool, retrieved DTC B163A and multiple network communication fault codes. Checked Body Control Module (BCM) power supply and ground circuits – normal. Inspected wiring between immobiliser coil and BCM, found loose connector. Measured immobiliser coil resistance at 1.2 Ω – normal. Suspected BCM software issue or hardware fault. Resolution: Disconnected, cleaned, and reconnected the harness connector between BCM and immobiliser coil, applied conductive grease. Reset BCM by disconnecting battery negative terminal for 5 minutes. Performed immobiliser system matching/learning with dedicated diagnostic tool. If fault persists, upgrade BCM software or replace BCM module. Note: This B163A code in the original case data relates to the immobiliser system. Depending on model and year, it may differ from airbag fault code definitions.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Song Pro smart key intermittent failure

✓
Symptoms: Smart key intermittently failed to unlock the vehicle. After entering the car, the message “Key Not Detected” appeared when pressing the start button. DTCs B163A and B163B were present simultaneously (weak key signal/authentication failure). Diagnosis: Connected a scan tool and retrieved B163A (immobiliser control unit communication fault). Checked smart key battery voltage (3.0 V, normal). Inspected the wiring between the cabin LF (low frequency) antenna and BCM; found the passenger-side LF antenna connector under the carpet had water ingress and oxidation. Measured the LF antenna inductance and found it was higher than normal (normal approx. 1.2 mH). Resolution: Cleaned and dried the LF antenna connector, then applied waterproof sealant. Replaced the passenger-side LF antenna. Performed key matching programming. Note: In the original case documentation, B163A relates to the immobiliser system. On other models or model years, this DTC may be defined as an airbag fault.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Qin Plus DM-i won't start after accident repair

✓
Symptoms: After front-end accident repairs, the vehicle wouldn't start. The instrument cluster showed an immobiliser active warning. Stored fault code: B163A (immobiliser internal fault). Diagnosis: Scanned for codes: B163A and multiple U-series communication codes. Inspected the repaired area and found the front compartment harness connector (BCM power) not fully seated. Checked BCM fuses: F2/14 (10A) blown. Measured BCM voltages: ACC power normal, constant B+ unstable. Traced the circuit and found body harness damage from the accident repair, causing an intermittent short circuit. Resolution: Repaired the damaged harness and re-insulated it. Replaced the blown fuse. Reconnected all BCM connectors and confirmed they locked securely. Used a VDS diagnostic tool to reset the immobiliser and match the keys. Note: In this case, B163A relates to the immobiliser system. Depending on model and year, the definition may differ — in some vehicles this code is for the airbag system.
Original source ↗
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD Han EV: Immobiliser matching after BCM replacement

✓
Symptoms: After fitting a new Body Control Module (BCM), the vehicle would not start and the instrument cluster displayed "Check Anti-theft System". Read DTC B163A (Immobiliser Control Unit Not Configured/Communication Interrupted). Diagnosis: Confirmed the replacement BCM part number matched the original. Checked the BCM coding/configuration; the new BCM was missing the VIN and immobiliser configuration data. Inspected the transponder coil connection and found it normal; the key chip functioned correctly. Used a scan tool to read the BCM live data, which showed the immobiliser status as "Inactive". Repair procedure: Connected a BYD-specific diagnostic tool (VDS or Launch X431). Navigated to "Special Functions" → "BCM Configuration" and wrote the vehicle VIN. Performed "Immobiliser System Matching": matched the key, engine ECU, and BCM in sequence. Cleared the fault codes after completing the matching. The vehicle started normally. Note: In the original case materials, B163A relates to the immobiliser system and may differ from current airbag fault code definitions depending on vehicle model and year.
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]