AU
B163A1A

This fault code indicates the front passenger side airbag igniter circuit resistance measures 0 ohms, indicating a Short to Ground fault — Seal U

Safety System

This fault code indicates the front passenger side airbag igniter circuit resistance measures 0 ohms, indicating a Short to Ground fault.

Normal airbag igniter resistance in the SRS (Supplemental Restraint System) is typically 1.5-3.0 Ω.

A 0 ohm reading indicates a direct ground path in the circuit.

Damaged wiring harness insulation contacting ground, shorted connector terminals, or an internal short circuit in the airbag module igniter can cause this condition.

This fault triggers the SRS control unit fail-safe mode, illuminates the airbag warning light, and can prevent the passenger side airbag from deploying during a collision, severely compromising occupant side impact protection.

BYD E2/E3 and similar models use seat-integrated side airbags; frequent seat adjustment easily causes wiring harness fatigue damage.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Front passenger seat side airbag wiring harness worn and shorted (seat rail pinching or long-term use fatigue damages the insulation, causing a short to ground).
  • 2Water ingress, corrosion, or poor terminal contact at the yellow SRS connector under the seat causing a short circuit (common after vehicle wading or improper interior cleaning)
  • 3Side airbag module (gas generator) internal igniter short circuit failure (manufacturing process defect or aging)
  • 4SRS control unit internal detection circuit fault (damaged control unit ECU chip or faulty sampling resistor; relatively rare)
  • 5Wiring harness crushed or pinched during front passenger seat modification, removal, or installation, exposing the conductor core and causing a short to ground.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS2000/VDS2100) to read the complete DTCs and freeze frame data. Confirm B163A1A is present as a static fault and record the environmental data at the time of the fault.
  • 2
    Disconnect the battery negative terminal and wait at least 3 minutes to fully discharge the SRS capacitor. Never measure the airbag circuit directly while powered on.
  • 3
    Inspect the front passenger seat side airbag wiring harness (especially the yellow connector and harness sleeve at the seat-to-body connection) for wear, damaged insulation, or pinch marks. Focus on the area near the seat slide rail mounting points.
  • 4
    Disconnect the SRS connector under the seat (yellow plug, usually containing a shorting bar). Bridge the circuit using the dedicated airbag load tool (2Ω simulated resistor), turn the power back on, and read the fault code: if the fault changes to 'resistance too high' or disappears, the circuit is normal and the fault is in the airbag module; if the fault remains, check the wiring harness for continuity to ground.
  • 5
    Use a multimeter to measure the resistance to ground at both ends of the airbag wiring harness (measure the SRS ECU end and the airbag end separately) to check for a short to ground. Focus inspection on the wiring harness near the seat slide rail and inside the B-pillar trim panel.
  • 6
    If the wiring harness is damaged, repair it with high-temperature insulating tape or replace the wiring harness. If the airbag module has an internal short circuit, replace the front passenger side airbag module (replace the seat trim or side airbag assembly simultaneously, depending on the vehicle structure; never disassemble the airbag module yourself).
  • 7
    Reconnect all connectors, ensure the yellow SRS plug locks into place (listen for a 'click'), and verify correct installation of the short-circuit protection tab.
  • 8
    Connect the battery, use the diagnostic tool to clear the fault code, run the SRS system self-diagnosis procedure, and read the igniter resistance value. Confirm DTC B163A1A does not return and the airbag warning lamp turns off. Finally, perform a seat fore-and-aft adjustment test to confirm there is no wiring harness interference.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

BYD E2 seat rail crushed wiring harness, causing short circuit

✓
The vehicle came into the workshop with the airbag warning light on solid on the instrument cluster. DTC B163A1A was read. Inspection revealed the front passenger seat was an aftermarket add-on, and the wiring harness had been routed incorrectly during installation. Removing the seat showed the side airbag harness crushed by a seat rail mounting bolt, with its copper core in direct contact with the metal seat frame, causing a short to ground. Repair: Replaced the damaged harness section, re-routed the wiring, added corrugated tubing for protection, and made sure the harness would not be pinched throughout the full range of seat adjustment. After the repair, the airbag light went out and the system returned to normal.
BYD DTC AI AnalysisFrom Chinese market (translated)

Water ingress corrosion in the passenger-side airbag connector of a BYD Qin EV.

✓
A 2019 Qin EV developed an illuminated airbag warning light after driving through flood water during a heavy rainstorm. The scan tool showed DTC B163A1A. Inspection found water ingress marks on the carpet and green copper corrosion inside the yellow SRS connector under the front passenger seat. Electrolyte conduction between the terminals caused a short circuit. Disconnected the connector, cleaned the terminals thoroughly with electronic contact cleaner, blew them dry, applied conductive grease, and replaced the waterproof seal. Checked body drain holes for blockages and cleared rear door drain channels. Cleared the fault codes and road-tested; the fault did not return.
BYD DTC AI AnalysisFrom Chinese market (translated)

Frequent seat adjustment caused wiring harness fatigue fracture in E3 commercial vehicle.

✓
A BYD E3 rideshare vehicle with 120,000 km logged DTC B163A1A. Due to commercial use, frequent forward and backward adjustment of the front passenger seat caused the protective sleeve of the airbag wiring harness between the seat and body to crack. Internal wires suffered insulation damage from repeated flexing, with multiple cores shorting to ground. Inspection during repair revealed clear fatigue fracture characteristics where the harness exits the protective sleeve. Fix: Replaced the entire seat wiring harness assembly (including the airbag circuit), adjusted harness mounting points to increase slack, and securely fastened the protective sleeve. No recurrence after one month of post-repair monitoring.
BYD DTC AI AnalysisFrom Chinese market (translated)

Replaced the passenger seat side airbag module to resolve the internal short circuit.

✓
Following a minor side impact, the front passenger side airbag deployed normally. After the dealership replaced the airbag module with a new one and cleared the DTCs, the airbag warning light illuminated again the next day with DTC B163A1A returning. Checked the wiring harness – normal. Used a dedicated resistance tester to directly measure the new airbag module. Resistance: 0.2 Ω (normal is approximately 2.0 Ω), indicating a parts quality issue (internal igniter short circuit). Replaced with another genuine airbag module; resistance measured 1.9 Ω. Installed it, completely eliminating the fault. Recommendation: After replacing an airbag module, always directly measure its resistance to confirm part quality.
BYD DTC AI AnalysisFrom Chinese market (translated)

Misdiagnosed SRS control unit internal sampling circuit fault case

✓
Multiple repairs failed to resolve DTC B163A1A on a BYD E2. Replaced the wiring harness and airbag module, but the fault persisted. Checked the drive signal from the SRS ECU to the airbag using an oscilloscope and found abnormal output voltage during the control unit self-test. Further measurement of the internal sampling resistor in the ECU revealed a short to ground. Confirmed that the SRS control unit (ACU) internal circuit board had corrosion from moisture ingress (the vehicle previously had a water leak from a blocked sunroof drain tube). Replaced the airbag control unit, recoded the system, and completely cleared the fault. This case highlights that after ruling out wiring and airbag module faults, consider the control unit itself.
Other Seal U 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]