AU
B16BB

DTC B16BB indicates the Airbag Control Unit (SRS_ECU) detected a severe fault during its internal self-test — Atto 3

Safety System

DTC B16BB indicates the Airbag Control Unit (SRS_ECU) detected a severe fault during its internal self-test.

This typically points to a hardware-level fault in the ECU internal processor, memory, power regulation circuit, or ignition driver circuit.

This means the SRS_ECU cannot execute the crash detection algorithm, cannot drive the airbag ignition circuits, or detected a program memory error during the cyclic redundancy check (CRC).

This safety-critical fault forces the entire airbag system into fail-safe mode.

During a collision, all airbags (front airbags, side curtain airbags, knee airbags) and seat belt pretensioners may fail to deploy.

The fault may also affect the active head restraint and crash fuel cut-off functions.

The B16BB fault code on the Atto 3 indicates a medium-severity internal fault in the airbag control unit. The system may enter fail-safe mode, so airbags and seat belt pretensioners may not deploy in a crash. Common causes include voltage surge damage from jump-starting or a 24V connection, or corrupted ECU memory. The recommended fix is to visit an authorised dealer for diagnosis and ECU repair or replacement. Typical repair cost data is available.
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Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Reversed polarity during jump-starting, alternator voltage regulator failure, or incorrect connection to a 24V power supply often burns out the SRS ECU internal power supply chip or voltage regulator circuit.
  • 2ECU internal EEPROM memory data corruption, possibly due to a high-current surge during a vehicle collision, electromagnetic interference (EMI), or interrupted software flashing.
  • 3ECU seal failure causes internal PCB corrosion, commonly occurring after driving through water, a blocked and leaking sunroof drain tube, or long-term parking in a high-humidity environment.
  • 4ECU internal acceleration sensor (MEMS) or safing sensor signal processing circuit fault causing self-test failure.
  • 5Oxidized wiring harness connector pins or backed-out terminals cause a poor ECU power supply or ground connection, repeatedly triggering the ECU internal low-voltage reset (brown-out).
What To Do
  • 1
    Use the VDS3000 diagnostic tool to perform a full SRS system scan. Confirm B16BB is a current fault (Active) and will not clear. Check for accompanying communication fault codes (such as codes starting with U).
  • 2
    Check the SRS ECU power supply: Measure the voltage at connector terminal 30 (constant +B) and terminal 15 (ignition switch power); the voltage must be 9-16V. Measure the resistance between ground terminal 31 and body ground; the resistance must be less than 0.5Ω.
  • 3
    Check CAN communication: Measure terminals 6 (CAN-H) and 14 (CAN-L) at the diagnostic port. Idle voltages should be 2.6V and 2.4V respectively, differential voltage should be 1.8-2.7V, and the waveform should show no distortion.
  • 4
    Visually inspect the ECU housing: check for cracks, water marks, and corrosion. Pay special attention to drink spills on Yuan/Qin models, where the ECU mounts beneath the center tunnel.
  • 5
    Perform ECU removal and inspection: Disconnect the battery negative terminal and wait 3 minutes (for capacitor discharge). Remove the ECU and check the connector pins for oxidation (green/white). Check the interior for signs of water ingress or a burnt smell.
  • 6
    If the above checks are normal, replace the SRS ECU with one of the same part number (Note: ECU hardware versions differ between BYD models; verify the part number, such as EG-3636000-X).
  • 7
    After installing the new ECU, perform online programming (Coding): Use VDS3000 to write the vehicle VIN and airbag configuration parameters (number of airbags, knee airbag presence, seat occupancy recognition type, etc.).
  • 8
    Perform system configuration: calibrate the seat occupancy sensor, learn the steering wheel clock spring center position, and perform a crash simulation test (use the dedicated load box instead of the actual airbag to verify the ignition circuit function).
Real-World Cases
BYD DTC AI Analysis

2021 BYD Tang DM SRS ECU internal power supply fault

✓
Vehicle dash displayed 'Check SRS System'. Scanned DTC B16BB-00. Inspection found an aftermarket audio system had been installed. The installer mistakenly connected the SRS ECU power wire in parallel with the amplifier power wire when tapping constant power, causing voltage to drop below 6V during cranking. This damaged the power management IC inside the SRS ECU. Replaced the SRS ECU and restored the factory wiring harness. Fault resolved. Total repair cost approx. 3200 yuan.
BYD DTC AI Analysis

2019 BYD Yuan EV: SRS fault after water wading

✓
After driving through water, the airbag warning light stayed on constantly and DTC B16BB was set. Disassembly and inspection found the SRS ECU beneath the center console had a deteriorated housing seal ring, allowing water to seep through the wiring harness boot and corrode the PCB, causing a short circuit. Cleaned and dried the wiring harness connector, installed a new ECU (Part No. EG-3636000-A2), and applied additional waterproof sealant during installation. Fault resolved.
BYD DTC AI Analysis

BYD Song MAX 2019: ECU locked after collision

✓
The vehicle sustained a minor frontal impact (airbags did not deploy). After repairs, technicians could not clear DTC B16BB. Investigation revealed that when the impact sensor triggered, the ECU logged a collision event flag internally and locked the system. Although the impact did not reach the airbag deployment threshold, the ECU entered an irreversible fault mode. Replaced with a new ECU and recalibrated the seatbelt pyrotechnic pretensioner; the system then returned to normal.
BYD DTC AI Analysis

2020 BYD Qin Pro: Software flash bricked the ECU

✓
During an SRS system software upgrade at the dealership, the diagnostic tool lost its network connection, causing incomplete ECU programming. The instrument cluster displayed an SRS fault, and the VDS could not communicate. The ECU entered Bootloader mode, but the main program was corrupted, triggering DTC B16BB (hardware fault). Replaced the ECU hardware and reflashed the software using the latest VDS3.0. Fault eliminated.
BYD DTC AI Analysis

BYD Tang II intermittent B16BB fault

✓
The airbag warning light intermittently illuminates when driving on rough roads, but remains off when stationary. Inspection revealed ECU earth point G202, located beneath the left A-pillar, had resistance fluctuating between 0.5-8Ω due to paint residue from assembly. Sanded the earth point and retightened the bolt to 9N·m. Cleared the fault codes and monitored for one month with no recurrence.
Other Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.
Common problems reported for Atto 3 →Atto 3 overview →
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.