AU
B16BC

DTC B16BC indicates the airbag control unit (SRS ECU) detects an internal system fault or critical safety circuit abnormality — Seal U

Safety System

DTC B16BC indicates the airbag control unit (SRS ECU) detects an internal system fault or critical safety circuit abnormality.

Specifically, this fault typically indicates an SRS ECU internal processor self-test failure, corrupted non-volatile memory (NVM) data, a power management module fault, or a communication interruption between the driver-side Occupant Classification System (OCS) and the ECU.

BYD e-platform models integrate the SRS ECU near the body control module.

The ECU monitors crash sensors, seat belt pretensioners, airbag ignition circuits, and seat occupancy status.

This fault may prevent the airbag system from deploying correctly during a collision or trigger a warning without a collision.

It constitutes a critical fault affecting passive safety.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal hardware fault: Voltage fluctuations, static electricity, or aging usually damage the control unit's internal processor, memory, or power voltage regulator chip.
  • 2Driver seat Occupant Classification Sensor (OCS) fault: Damaged seat pressure sensor, or abnormal signal caused by a loose wiring harness connector, water ingress, or oxidized pins.
  • 3Abnormal power supply: Blown SRS ECU power supply fuse (such as the SB03/IG1 power supply in the instrument panel fuse box), battery voltage below 9V or above 16V, or poor contact in the ground circuit.
  • 4CAN communication bus fault: SRS system lost communication with the vehicle CAN network. Possible causes include a wiring harness short circuit, open circuit, or electromagnetic interference.
  • 5Software or calibration data fault: Outdated SRS ECU internal software, incomplete flashing, or failure to perform the replacement reset procedure after a collision, causing data verification failure.
What To Do
  • 1
    Safety preparation: Switch the vehicle OFF, disconnect the negative battery terminal, and wait at least 3 minutes to fully discharge the airbag system and prevent accidental deployment.
  • 2
    Initial diagnosis: Use the BYD VDS2000/VDS6000 diagnostic tool to access the SRS system, read the complete fault code list and freeze frame data, and check for accompanying B16BB (SRS_ECU internal fault), U-series communication faults, or seat occupancy-related fault codes.
  • 3
    Power supply and ground check: Check the SRS ECU-related fuse in the instrument panel fuse box (typically IG1 power). Measure the ECU connector terminal voltage (standard: 9-16V) and ground resistance (< 1Ω). Check the battery voltage and charging system status.
  • 4
    Seat occupancy system check: Remove the driver's seat. Inspect the OCS sensor connector under the seat (usually a yellow or white plug) for looseness, water ingress, corrosion, or wiring harness damage. Measure the sensor resistance (standard range: 2-5kΩ; refer to the vehicle repair manual for specific values).
  • 5
    Wiring harness and communication check: Check wiring harness continuity from the SRS ECU to the seat and the crash sensor. Measure CAN-H and CAN-L voltage (approx. 2.5V) and termination resistance (approx. 60Ω). Eliminate wiring short circuits or interference.
  • 6
    Software procedure: If the wiring is normal, update the SRS ECU software (if a new version is available) or reset the control unit. Clear the fault code, perform a 20-minute road test, and observe if the fault recurs.
  • 7
    Hardware replacement: If the above steps fail, inspect the SRS ECU exterior for signs of burning, cracks, or water ingress. Replace the airbag control unit if necessary. Perform online coding, write configuration parameters, and calibrate the system (some models require special equipment to write the VIN and clear crash records).
Real-World Cases
BYD DTC AI Analysis

Seat water ingress caused OCS sensor short circuit in Yuan EV

✓
A 2019 BYD Yuan EV came in with the SRS warning light constantly on. Retrieved DTC B16BC. Found the vehicle had recently had its interior cleaned, with standing water beneath the driver's seat. Removed the seat and found water inside the OCS sensor connector; the terminals had oxidised and turned black. Used compressed air to clean and dry the wiring harness, applied conductive grease to the terminals, and reconnected the connector. Cleared the fault. Advised the owner to avoid pouring water directly onto the seats when cleaning.
BYD DTC AI Analysis

Tang DM unstable battery voltage caused ECU self-test failure

✓
2021 BYD Tang DM. The owner reported the airbag warning light occasionally came on during cold starts, going out after driving for a while. The scanner showed historic DTC B16BC. Freeze frame data showed the battery voltage was 8.2V when the fault occurred. Inspection found the battery had deteriorated, causing a severe voltage drop on cold starts. Replaced the battery and checked the charging system (alternator output 13.8–14.4V, normal). The fault has not returned. Root cause: low voltage caused SRS ECU initialisation failure.
BYD DTC AI Analysis

Song MAX SRS ECU not reset after collision repair

✓
Repaired a 2019 BYD Song MAX after a minor front impact. Replaced the front bumper and left collision sensor. The airbags had not deployed. Post-repair, the instrument cluster displayed an airbag fault and logged DTC B16BC. Inspection found the shop had not cleared the SRS ECU's collision data or reconfigured it. Performed the 'Airbag Control Unit Replacement' procedure using the BYD dedicated diagnostic tool, wrote new configuration data, and cleared collision records. The system returned to normal.
BYD DTC AI Analysis

Qin Pro (Petrol) CAN harness chafing causing communication fault

✓
2020 BYD Qin Pro petrol. Intermittent airbag warning light on rough roads. Stored DTCs B16BC and U0151 (lost communication with SRS). Checked SRS ECU connector – normal. Traced the body floor harness and found it rubbing against the seat slide rail. CAN-H wire insulation worn through, causing intermittent short to ground. Repaired the harness, re-secured and rerouted it clear of the seat travel area. Fault resolved.
BYD DTC AI Analysis

Outdated software version on the Yuan EV caused false alarms.

✓
2019 BYD Yuan EV with no accident history or water ingress intermittently set fault code B16BC. Checked the wiring and sensors; all normal. Consulted a BYD technical bulletin and found that the SRS ECU software in this production batch has a bug causing false ECU fault reports at specific temperatures. Used the VDS diagnostic tool to upgrade the SRS system software from V1.02 to V1.05. The fault has not returned since the upgrade.
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.