AU
B16BD

SRS ECU (Airbag Electronic Control Unit) internal self-test fault or abnormal external communication/power supply — Seal U

Safety System

SRS ECU (Airbag Electronic Control Unit) internal self-test fault or abnormal external communication/power supply.

This DTC indicates the Airbag Control Unit (ACU) detected a functional fault in its processor, memory, power management circuit, or critical sensor interfaces during the self-test.

This triggers the system to enter fail-safe mode (disabling all airbags, seat belt pretensioners, and the crash fuel cut-off function).

Specific fault conditions include: 1) ECU internal hardware damage (e.g., BGA chip cold solder joints or aging electrolytic capacitors); 2) Abnormal impedance in the 12V power supply or ground circuit causing an ECU reset; 3) CAN network communication interruption (loss of synchronization with the vehicle control unit and instrument cluster); 4) Short or open circuit in the signal links of critical safety sensors (front impact sensor, side impact pressure sensor, seat occupancy sensor) exceeding the calibrated threshold.

This fault may prevent airbag deployment during a collision or risk unintended static deployment.

Immediately remove the vehicle from service and perform repairs.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1SRS ECU internal hardware fault: main control chip (e.g., NXP SPC56 series) memory checksum failure, internal voltage regulator module damage, capacitor aging and leakage causing power supply ripple to exceed limits.
  • 2Power supply system fault: battery voltage below 9V or above 16V; poor contact in the ECU constant power (B+) or ignition power (IGN) circuit (loose connector, poor fuse connection); oxidized ground point causing increased resistance (>1Ω)
  • 3CAN bus communication fault: Wiring harness short/open circuit between SRS and diagnostic CAN (or private CAN), terminating resistor drift (deviating from 60Ω±5Ω), electromagnetic interference causing message loss.
  • 4Abnormal sensor signal: Front impact sensor internal short circuit, seat occupancy detection sensor (SBR) short to ground, or damaged side airbag pressure sensor signal harness causing the ECU to falsely detect an internal fault.
  • 5Software/configuration error: Replacement ECU not programmed online after accident repair (VIN not written, incorrect vehicle configuration code), corrupted calibration data, or interrupted flashing process causing incomplete firmware.
What To Do
  • 1
    Safety preparation and initial inspection: Disconnect the negative battery terminal and wait at least 3 minutes to discharge the energy storage capacitors. Visually inspect the SRS ECU housing for physical damage, water ingress, or burn marks. Inspect the ECU connector (usually yellow) located under the center console or floor for looseness, backed-out pins, or corrosion.
  • 2
    Power supply and ground diagnosis: Restore power (do not start vehicle). Use a multimeter to measure the voltage at ECU connector terminal 30 (constant power) and terminal 15 (IGN). Standard: 12V±0.5V. Measure the resistance between the ground point and vehicle body. Standard: Less than 1Ω. Use an oscilloscope to check the power supply ripple. Peak value must be less than 100mV.
  • 3
    Communication network check: Measure the voltage to ground of diagnostic CAN-H (OBD pin 6) and CAN-L (pin 14) (static voltage should be approximately 2.5 V; CAN-H high level 3.5 V, CAN-L low level 1.5 V). Disconnect the power and measure the terminal resistance (disconnect the ECU connector and measure its internal resistance; it should be approximately 60 Ω).
  • 4
    Sensor circuit check: Use the diagnostic tool to read the live data stream. Check the status of each crash sensor and the seat occupancy sensor resistance (normally several hundred ohms to several kΩ). Disconnect all sensors. Measure the ECU-side wiring harness for shorts to ground or power.
  • 5
    ECU unit verification: Perform a swap test using a known-good SRS ECU from the same vehicle model (Note: communication test only; do not deploy airbags). If the fault code transfers, the original ECU is faulty. Alternatively, measure the continuity of the ECU internal fuse (some models have a built-in resettable fuse).
  • 6
    Replacement and configuration: After replacing the SRS ECU with a new unit, perform the following: ① Write the VIN and vehicle configuration code via online programming; ② Set the crash threshold parameters; ③ Perform a system self-check (including resistance checks for all circuits); ④ Clear fault codes and perform a simulated crash test (using dedicated equipment, not an actual vehicle crash) to verify system function.
Real-World Cases
BYD DTC AI Analysis

2021 Tang DM-i SRS ECU power fluctuation causing intermittent fault codes

✓
Airbag warning light illuminated intermittently while driving. Retrieved DTC B16BD with intermittent status. Inspection revealed oxidation on the battery negative earth point (located at the left front chassis rail), measuring 3.2Ω resistance. Cleaned the earth point, but power supply ripple still intermittently exceeded limits (reaching 200mV). Traced to an ageing voltage stabilising capacitor inside the ECU. Replaced the SRS ECU and reprogrammed to resolve the fault. Key point: Also check the external power supply quality to avoid damaging the replacement ECU.
BYD DTC AI Analysis

2019 BYD Yuan EV: Seat occupancy sensor short circuit triggers ECU protection

✓
On start-up, the instrument cluster displayed an airbag fault. The scan tool read DTC B16BD, which would not clear. Found the front passenger seat occupancy sensor (SBR) wiring harness under the seat had been chafed by the seat slide rail, shorting the signal wire to ground (0.8 Ω). The SRS ECU detected abnormal current in the sensor loop, triggered its internal protection mechanism, and logged an ECU fault. Repaired the harness insulation, replaced the damaged sensor, and cleared the codes. The system returned to normal. These faults are easy to misdiagnose as an ECU failure – rule out peripheral short circuits first.
BYD DTC AI Analysis

2019 Song MAX: Configuration error after accident repair caused B16BD

✓
After a front-end collision, an unauthorised repair shop replaced the airbags and SRS ECU, but the SRS warning light stayed on with DTC B16BD. I checked with the factory diagnostic tool and found the ECU had a mismatched VIN and was missing configuration parameters (airbag count, seatbelt pretensioner setup). I performed online programming using the BYD-specific VDS2000/3000 tool, wrote the correct VIN, configuration codes and calibration data, then executed system configuration coding. I successfully cleared the fault code and the system passed the self-test.
BYD DTC AI Analysis

2020 Qin Pro DM: CAN bus interference caused SRS ECU communication failure

✓
After fitting a 360-degree surround view camera system, the SRS warning light came on intermittently, accompanied by DTCs B16BD and U0155 (communication fault with the instrument cluster). Inspection found the added reversing camera's CAN wire had been spliced into the SRS system's private CAN bus (not the diagnostic CAN), causing signal conflicts and voltage irregularities. After restoring the original wiring harness and moving the camera system to the infotainment CAN, the SRS ECU communication waveforms returned to normal, eliminating the fault. Note: Some BYD models use a dedicated CAN network for the SRS ECU; unauthorised wiring taps are strictly prohibited.
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.