AU
B163B-00

DTC B163B-00 indicates the SRS (Supplemental Restraint System) ECU detects front passenger side airbag (typically seat side or curtain airbag) igniter circuit resistance below the calibrated threshold (normal range approximately 1 — Seal U

Safety System

DTC B163B-00 indicates the SRS (Supplemental Restraint System) ECU detects front passenger side airbag (typically seat side or curtain airbag) igniter circuit resistance below the calibrated threshold (normal range approximately 1.5-3.0 Ω; detected resistance <1.0 Ω or approaching 0 Ω).

This fault indicates a short circuit risk in the airbag igniter circuit, which can cause: 1) Airbag deployment failure during a collision, resulting in loss of occupant protection; 2) Unintended airbag deployment due to the short circuit in extreme cases.

The SRS enters fail-safe mode, illuminates the airbag warning light, and may disable the seat belt pretensioner function on some models.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Airbag igniter internal short circuit: Damaged heating wire insulation inside the airbag module shorts the positive and negative terminals, dropping resistance to near 0 Ω.
  • 2Wiring harness wear and short circuit: Repeated bending of the front passenger seat side airbag wiring harness at the seat adjustment slide rail damages the insulation, causing a short circuit between wires.
  • 3Connector water ingress and corrosion: Poor sealing of the airbag connector under the seat or lower B-pillar allows water ingress after wading, causing a short circuit between pins.
  • 4Clock spring (spiral cable) internal short circuit: Interlayer short circuit in the internal flat cable of the clock spring below the steering wheel (e.g., side airbag connecting through it).
  • 5SRS ECU detection circuit fault: ECU internal A/D converter or sampling resistor fault causes an abnormally low resistance reading.
What To Do
  • 1
    Safety preparation: Disconnect the low-voltage battery negative terminal, remove the high-voltage service disconnect switch (if applicable), and wait at least 90 seconds to ensure the SRS capacitor fully discharges. Do not measure the airbag igniter directly using a multimeter ohm setting.
  • 2
    Visual inspection: Verify the exterior of the front passenger seat side airbag and B-pillar curtain airbag is intact. Check the yellow SRS connector under the seat for water ingress, corrosion, or looseness. Check the wiring harness at the seat slide rail for signs of wear.
  • 3
    Circuit isolation diagnosis: Disconnect the airbag module connector and install a dedicated SRS diagnostic tool (or a 2Ω simulator resistor) in place of the airbag module. If the fault code changes to "open circuit", this confirms an internal short circuit in the airbag module. If the fault code remains "resistance too low", continue troubleshooting the wiring harness.
  • 4
    Harness resistance measurement: Disconnect the SRS ECU connector and measure the resistance between the positive and negative terminals of the front passenger airbag circuit. The normal reading is infinity (open circuit). A low resistance value indicates a short circuit between the harness wires.
  • 5
    Clock spring check (if applicable): If the fault involves the steering wheel airbag, remove the clock spring and measure its internal resistance. Normal resistance is <1Ω. Replace the clock spring if abnormal.
  • 6
    Component replacement: Replace the faulty airbag module, wiring harness, or clock spring. Verify all SRS connectors emit an audible 'click' when locking. Do not repair the SRS wiring harness; replace the entire harness.
  • 7
    System verification: Restore all connections, clear fault codes, and perform the SRS system self-test (turn the ignition ON and verify the warning lamp illuminates for 6 seconds, then turns off). Confirm the oscilloscope waveform (if available).
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin EV300 front passenger seat side airbag wiring harness chafed and short-circuited

✓
The vehicle is a 2017 BYD Qin EV300 with 80,000 km. The airbag warning light came on. The diagnostic scanner read DTC B163B-00 (passenger side airbag resistance too low). Removing the passenger seat revealed the seat side airbag wiring harness had chafed against the seat slide rails over time, wearing through the insulation and causing a short between the twisted pair wires. Measured resistance: 0.3 Ω. Replaced the passenger seat wiring harness assembly (including airbag connector). Fault cleared.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin 80: SRS connector short circuit due to water ingress after wading

✓
2017 BYD Qin 80. The dashboard displayed an airbag warning after driving in heavy rain. Retrieved DTC B163B-00 and measured the passenger side airbag circuit resistance at only 0.8 Ω. Inspection found the waterproof seal on the SRS connector under the seat had aged and fallen off; oxidised pins with verdigris caused a short circuit. Cleaned the pins with electronic cleaner, replaced the waterproof seal, applied conductive grease, and reconnected the connector. Resistance returned to 2.1 Ω, resolving the fault.
BYD DTC AI AnalysisFrom Chinese market (translated)

Qin EV450 airbag module internal short circuit false alarm

✓
2018 BYD Qin EV450, no accident history. Intermittent DTC B163B-00. When the fault occurred, airbag module resistance measured 0.5Ω (abnormal), returning to normal after cooling. Diagnosed as thermal breakdown short circuit of the airbag igniter's internal heating wire insulation. Replaced front passenger seat side airbag module (part number: SC-688XXX), performed SRS configuration write. Fault has not recurred.
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]