AU
B16BA

DTC B16BA indicates an internal fault or system-level communication fault in the airbag control unit (SRS ECU) — Seal U

Safety System

DTC B16BA indicates an internal fault or system-level communication fault in the airbag control unit (SRS ECU).

As the core controller of the passive safety system, the SRS ECU monitors crash sensor signals, evaluates crash severity, triggers airbag and seat belt pretensioner deployment, and continuously performs system self-diagnostics.

This DTC typically indicates an internal ECU microprocessor fault, an EEPROM data checksum failure, a power supply monitoring circuit abnormality, or a CAN bus communication interruption.

The ECU sets this DTC and enters degraded mode when it detects an internal circuit fault, a supply voltage outside the normal 9-16V range, or a loss of communication with the vehicle network exceeding the specified time (typically >500ms).

In this state, the vehicle may completely lose crash protection functions (airbags will not deploy) or risk unintended deployment.

This constitutes a high-risk safety fault.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal hardware fault: internal capacitor aging and leakage, MCU crash, memory data corruption (EEPROM checksum error); affects 2018-2020 controller batches.
  • 2Power supply system fault: battery voltage below 9V or above 16V, excessive contact resistance in the IGN+ power circuit (>1Ω), or loose or oxidized ECU ground wire, causing ECU reset or unstable operation.
  • 3CAN network communication fault: Short or open circuit in the Powertrain CAN (PT-CAN) or Body CAN (Body-CAN) wiring, or terminal resistance deviation (normal: 60Ω±5Ω), preventing the ECU from communicating with the Vehicle Control Unit.
  • 4Peripheral component short circuit/overload: A short to power or ground in the front crash sensor, side airbag module, or seat occupancy recognition sensor circuit triggers the ECU internal protection circuit and logs a hardware fault.
  • 5Software/calibration data error: Interrupted OTA update, diagnostic tool flashing failure, or missing online configuration (Online Coding) after an accident results in lost internal ECU parameters or version mismatch.
What To Do
  • 1
    Safety Preparation and Initial Inspection: Disconnect the 12V battery negative terminal and wait 3 minutes to discharge residual voltage. Inspect the SRS ECU exterior for physical damage, water ingress, or burn marks. Inspect the SRS-related fuses in the dashboard fuse box (usually 10A-15A) and the cabin wiring harness connectors (near the OBD port/GW connector).
  • 2
    Power supply and ground circuit test: Use a multimeter to measure the voltage to ground at ECU connector Pin30 (constant power +B) and Pin15 (IGN power). The standard value is battery voltage ±0.5 V. Measure the resistance to ground at ground Pin31; it must be <1 Ω. Check the connector terminals for backed-out pins, enlarged pin cavities, or green oxidation.
  • 3
    CAN bus communication diagnosis: Connect the VDS2000/Launch diagnostic tool, read the vehicle network topology, and check the SRS ECU communication status. Measure the voltage to ground of CAN-H (Pin 7) and CAN-L (Pin 8) (standard approximately 2.5V) and the resistance between them (standard approximately 60Ω, measure with power off) to rule out wiring short or open circuits.
  • 4
    Peripheral circuit continuity check: Use a dedicated probe or adapter to measure the circuit resistance of each crash sensor (front/side/center) and airbag module at the ECU connector (standard value: 2.0-3.0 Ω). Check for short to ground or short to power (resistance <1 Ω or >10 kΩ is abnormal).
  • 5
    Software flashing and configuration: If wiring is normal, perform 'SRS system online calibration' or 'ECU software upgrade' (requires a BYD DiLink authorized account). Rewrite the calibration data and write the configuration code (Coding). Clear the fault code and perform an ignition cycle test.
  • 6
    ECU replacement and matching: If the above steps fail, replace the SRS ECU with the same part number (distinguish between high-spec and low-spec versions). Execute the 'ECU Replacement' online matching procedure, synchronize the vehicle VIN and configuration parameters, and finally perform a system self-check (no fault codes) and a simulated airbag deployment test (using the dedicated tool).
Real-World Cases
BYD DTC AI Analysis

BYD Tang DM SRS light stays on after accident repair

✓
A 2021 Tang DM showed 'Check SRS System' on the instrument cluster after a minor rear-end collision. The technician retrieved DTC B16BA. Inspection found accident damage to the left front engine bay wiring harness. During the repair, the IGN power connector to the SRS ECU was not fully seated, causing a contact resistance of 3.2 Ω. The technician re-crimped the power terminal, measured contact resistance below 0.1 Ω, cleared the DTC, and the system returned to normal.
BYD DTC AI Analysis

12V battery power loss caused ECU reset fault on Yuan EV

✓
The owner of a 2019 Yuan EV reported the vehicle failed to start after being parked for one week. After a jump-start, the SRS warning light stayed on constantly and DTC B16BA was logged. Diagnosis found the battery voltage had dropped to only 8.5V. A voltage spike during the jump-start exceeded 18V, causing the SRS ECU internal memory data checksum to fail. Replaced the battery with an AGM unit, used a diagnostic tool to execute the 'SRS System Data Recovery' function, then reset the ECU. Fault resolved.
BYD DTC AI Analysis

ECU internal short circuit after water ingress - Song MAX

✓
A Song MAX drove through floodwater during heavy rain, causing the SRS system to fail and log code B16BA. Disassembly revealed the SRS ECU beneath the centre console had an aged seal; water ingress had corroded the PCB, and capacitor C102 had leaked. Resolution: Replaced the SRS ECU assembly, replaced the water-affected harness connectors, performed online programming and matching, and checked the insulation of all airbag modules.
BYD DTC AI Analysis

Short in Qin Pro side airbag circuit triggers ECU protection

✓
2020 Qin Pro: SRS warning light came on after seat cover replacement. Fault codes B16BA and B1620 stored (driver side airbag fault). Inspection found the seat rails had pinched and damaged the side airbag wiring harness during seat removal and installation, causing two wires to short to ground. The SRS ECU detected the circuit abnormality, entered protection mode and reported an ECU hardware fault. Repaired the wiring harness insulation, replaced the damaged side airbag module and cleared the fault codes.
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.