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 — Seal U

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 — Seal U
  • 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).
  • 2Worn internal slip ring in the spiral cable (clock spring), poor contact, or partial open circuit causing unstable signal transmission resistance.
  • 3Aging, cold solder joints, or partial breakage of the internal igniter resistance wire in the side airbag module, resulting in increased internal resistance.
  • 4Frequent seat position adjustment causes fatigue fractures in the seat wiring harness copper wires (partially broken, leaving only a few strands connected), creating a high-resistance circuit.
  • 5Sampling resistor drift in the airbag ECU internal monitoring circuit, or a false software report (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 at the time of the historical fault, and the vehicle status.
  • 3
    Connector inspection: 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 conductive protective agent, and measure the resistance across both ends of the connector.
  • 4
    Component measurement: Remove the front passenger seat side trim panel, disconnect the airbag module connector, and use a high-precision multimeter to directly measure the airbag resistance (standard value: 2.0 ± 0.3 Ω; readings exceeding 3.5 Ω are abnormal).
  • 5
    Wiring harness inspection: Inspect the seat-to-body wiring harness conduit for wear, crushing, or partially broken copper wires caused by seat movement. Focus on the harness bends in the seat fore-aft adjustment area.
  • 6
    Clock spring inspection: If involving steering wheel or B-pillar connections (some models route the side airbag through the B-pillar), check the spiral cable (clock spring) for continuity and resistance stability.
  • 7
    Fault repair: If a high-resistance point exists, repair or replace the wiring harness; if the airbag unit resistance is abnormal, replace with an OEM side airbag module; if all components are normal, check the SRS ECU.
  • 8
    System reset: Reconnect all connectors (listen for a locking 'click'), reinstall components, connect the battery, use the diagnostic tool to clear the fault code and perform a system self-test, and confirm resistance 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 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]