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B16201B

B16201B is a BYD SRS (Supplemental Restraint System) diagnostic code indicating a communication interruption or open electrical connection between the driver's seat side airbag and the SRS control unit — Seal U

Safety System

B16201B is a BYD SRS (Supplemental Restraint System) diagnostic code indicating a communication interruption or open electrical connection between the driver's seat side airbag and the SRS control unit.

This DTC sets when the SRS ECU detects the driver's side airbag circuit resistance exceeds the standard range (typically 2.0-3.0Ω ±0.5Ω), indicating an open circuit or high resistance.

This incomplete airbag deployment circuit prevents the system from igniting the gas generator during a side impact.

This fault forces the SRS into a degraded mode.

The driver's seat side airbag becomes inoperative, but other airbags (front, curtain) typically remain functional.

Despite involving the high-voltage interlock and safety systems, the vehicle remains drivable with reduced occupant protection.

This fault continuously illuminates the instrument cluster airbag warning light on some models.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Loose yellow SRS connector or backed-out pins under the seat: Frequent fore-aft adjustment of the driver seat pulls the wiring harness, loosening the connector latch or causing poor terminal contact.
  • 2Clock spring internal open circuit: A broken flat ribbon cable inside the rotary connector beneath the steering wheel disrupts side airbag signal transmission (applicable to side airbag wiring harness connections integrated into the seat backrest).
  • 3Internal open circuit in the airbag module: Broken inflator bridge wire or corroded connector causes infinite circuit resistance.
  • 4Physical damage to the wiring harness: Worn harness sheath near the seat rail, broken or crushed conductors. Commonly caused by seat modifications or corrosion following water ingress.
  • 5SRS control unit software false fault: Early production ECU software is overly sensitive to resistance detection and falsely reports an open circuit fault in low temperatures.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal, wait at least 3 minutes for the SRS capacitors to discharge, wear an anti-static wrist strap, and disable the high-voltage system (for electric vehicles, disconnect the service disconnect switch).
  • 2
    Initial diagnosis: Use the BYD VDS or X-431 diagnostic tool to read all DTCs, confirm B16201B is a current fault rather than a history fault, and record freeze frame data (seat position, vehicle speed, etc.).
  • 3
    Visual inspection: Check the yellow SRS connector under the driver's seat (usually located on the inner side of the seat rail). Verify the connector is fully engaged and the locking tab is in place. Inspect the terminals for oxidation, burning, or backed-out pins.
  • 4
    Circuit measurement: Disconnect the airbag connector. Use a special probe (avoid piercing the wiring harness directly) to measure resistance on the harness side; normal value is 2-3Ω. Measure insulation resistance to ground; it should be greater than 10MΩ. Check wiring harness continuity while moving the seat through its full range of travel.
  • 5
    Component replacement test: Replace the original airbag module with a known-good airbag simulator (2.7Ω resistor). If the fault code clears, the airbag module is faulty. If the fault code remains, check the wiring harness continuity between the SRS ECU and the seat.
  • 6
    Clock spring check (if applicable): For models where the wiring harness passes under the steering wheel, check the continuity of each clock spring circuit. Turn the steering wheel and verify the measured resistance remains stable.
  • 7
    Repair verification: After repairing or replacing the faulty component, reconnect the battery, clear the fault code, and perform an SRS system self-check (turn the ignition switch ON and verify the airbag warning light turns off after 6 seconds). Perform a road test to verify the repair.
  • 8
    System calibration: For some models, execute 'Seat Position Sensor Calibration' and 'Airbag System Configuration Check' in VDS to write the parameters of the newly replaced airbag to the ECU.
Real-World Cases
BYD DTC AI AnalysisFrom Chinese market (translated)

Loose connector under E2 seat triggered intermittent warning

✓
Vehicle: 2019 BYD E2, 32,000 km. Symptoms: The airbag warning light on the instrument panel illuminates intermittently, especially on rough roads. DTC B16201B appears sporadically. Diagnosis: The yellow 2-pin connector under the driver's seat was not fully locked; the retaining clip showed wear. Cause: Frequent seat adjustment pulled the wiring harness during seat movement, loosening the connector. Fix: Re-seated and locked the connector, secured the harness routing with cable ties to avoid interference with the seat rails, cleared the fault code, and monitored for one week. No recurrence.
BYD DTC AI AnalysisFrom Chinese market (translated)

Internal open circuit in Qin EV seat airbag module

✓
Vehicle: 2019 Qin EV, post-accident repair. Symptoms: Airbag warning light stays on after repairs. VDS shows current fault code B16201B. Diagnosis: Harness side resistance normal at 2.4 Ω; airbag module side resistance infinite. Disassembled seat and found corroded internal pins on side airbag gas generator connector (water entered during accident, not fully dried). Solution: Replaced driver side airbag module (part no. EPB-5820100), coded and matched new module, cleared fault codes after bus communication test passed.
BYD DTC AI AnalysisFrom Chinese market (translated)

E3 seat rail wiring harness worn through, open circuit

✓
Vehicle: 2020 BYD E3, ride-share, 85,000 km. Symptoms: Airbag light always on, DTC B16201B. Fault code status changes when adjusting the seat. Diagnosis: Peeled back the harness protective sleeve under the seat. Found two wires nearly worn through at the seat rail corner, held by only a few copper strands. Cause: Long-term frequent seat adjustment caused the harness retaining clip to detach, letting the harness rub against the metal rail. Solution: Soldered and heat-shrink repaired the wires, rerouted the harness path, added anti-chafe sleeving, and adjusted harness length slack.
BYD DTC AI AnalysisFrom Chinese market (translated)

SRS ECU software false alarm upgrade case

✓
Vehicle: 2019 Qin EV, driven in cold climates. Symptoms: DTC B16201B appeared intermittently during cold morning starts, self-cleared as temperature rose; wiring harness readings normal. Diagnosis: Comparison with same-period models confirmed early ECU software (V1.2) set resistance detection thresholds too strict for low temperatures. Resolution: Upgraded SRS control unit software online to V1.5 via VDS. The new software optimizes the resistance compensation algorithm for low-temperature conditions. DTC has not returned since the upgrade.
BYD DTC AI AnalysisFrom Chinese market (translated)

Seat modification damaged the wiring harness connector.

✓
Vehicle: 2020 E3, after installing sport seats. Symptoms: Airbag light came on immediately after the modification, setting DTC B16201B. Diagnosis: Inspection found the shop cut the original harness to connect the new seats directly instead of using the OEM SRS adapter. This caused poor terminal contact and reverse polarity risk. Solution: Restored the original vehicle harness (ordered a new harness assembly), used the OEM-specified seat adapter harness, and matched airbag circuit impedance. Cleared fault codes and the system returned to normal.
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]