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B16A5

DTC B16A5 indicates an internal self-diagnostic fault in the airbag control unit (SRS ECU) — Atto 3

Safety System

DTC B16A5 indicates an internal self-diagnostic fault in the airbag control unit (SRS ECU).

The SRS ECU is the core control module of the safety system, responsible for monitoring crash sensors and controlling airbag deployment, seat belt pretensioners, and seat occupancy detection.

This fault code specifically points to a hardware-level abnormality in the ECU internal processor, memory (EEPROM/Flash), power supply monitoring circuit, or clock circuit, rather than an external wiring or sensor fault.

This internal fault can force the airbag system into fail-safe mode, preventing normal airbag deployment during a collision or creating a risk of unintended deployment, making it a severe safety fault.

Upon detecting the fault, the ECU illuminates the airbag fault warning light and may disable related functions such as the seat belt pretensioners and child monitoring system.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Power supply system fault: Unstable battery voltage (continuously below 9V or above 16V), poor contact in the SRS ECU power supply circuits (B+, IGN), or transient overvoltage damaging the internal power management chip.
  • 2Internal memory fault: EEPROM data corruption, Flash memory read/write error, or checksum failure. Typically results from software bugs, electromagnetic interference, or incomplete software updates.
  • 3ECU hardware aging: poor internal PCB solder joints, capacitor aging, processor crystal oscillator failure, or internal chip circuit breakdown (common in high-temperature, high-humidity environments or after driving through water).
  • 4Software version defect: Specific ECU software batches contain logic flaws that trigger an internal watchdog reset failure under certain operating conditions, such as frequent power-on self-tests or CAN communication congestion.
  • 5Strong electromagnetic interference: Unauthorized installation of high-power radio equipment, xenon lamps, or inverters interferes with the ECU internal analog-to-digital conversion circuit, causing the self-diagnostic program to falsely detect an internal fault.
What To Do
  • 1
    Use a BYD dedicated diagnostic tool (ED400 or VDS) to read the complete DTC information. Record the freeze frame data (vehicle speed, timestamp, voltage value) and confirm whether B16A5 is a current or history code.
  • 2
    Perform a full vehicle scan and check for U-class communication fault codes (such as U0100 or U0151) to rule out false internal faults caused by CAN bus interference.
  • 3
    Check the battery voltage and charging system. Measure the static voltage (should be 12.4V-12.8V), cranking voltage (should be ≥9.6V), and charging voltage (should be 13.8V-14.8V). Repair any power supply system faults.
  • 4
    Disconnect the battery negative terminal and wait at least 3 minutes for the SRS capacitor to fully discharge. Reconnect the terminal, perform an ECU reset, and observe if the fault code reappears.
  • 5
    Check the SRS ECU exterior and installation area for signs of water ingress, physical damage, or corrosion. Check the wiring harness connector (usually located under the center console or in front of the gear selector) for oxidation or backed-out pins.
  • 6
    Update the SRS ECU software: Use the diagnostic tool to check for the latest software version (such as a patch for B16A5). Perform programming strictly according to the BYD Technical Service Bulletin (TSB). Maintain stable voltage during programming (use a regulated power supply).
  • 7
    Measure the SRS ECU power supply, ground, and CAN lines: Check the continuity and voltage drop of B+ (constant power), IG (ignition power), and GND (ground). Measure the CAN-H and CAN-L waveforms (dominant level 2.5V-3.5V, recessive level 2.5V, differential voltage 1.5V-2.5V).
  • 8
    If the above steps fail, replace the SRS ECU assembly using genuine parts. After replacement, perform online programming (Coding) and safety configuration (write the VIN, seat configuration, airbag level, and other parameters). Perform a system self-check and pass the crash simulation test (use the diagnostic tool actuator test function; do not perform a physical crash).
  • 9
    Before delivery, perform a road test and monitor the SRS data stream. Verify no fault codes return and check that the airbag warning light turns off normally after the self-check.
Real-World Cases
BYD DTC AI Analysis

Song MAX alternator overvoltage damaged the SRS ECU

✓
2019 BYD Song MAX DM, 42,000 km. Instrument cluster displayed 'Check SRS System'. Scan tool retrieved DTC B16A5 (current fault), freeze frame data showed system voltage at 16.8V when the fault occurred. Inspection found a faulty alternator regulator; output voltage fluctuated between 15.5V and 17.2V. The SRS ECU's internal overvoltage protection circuit triggered, locking its power management chip. Repair: Replaced alternator assembly, then power-cycled and reflashed the SRS ECU using a regulated 14V power supply. Fault resolved. Recommend checking vehicle wiring harness insulation to prevent potential damage to other ECUs from prolonged overvoltage.
BYD DTC AI Analysis

Software data verification failed after accident repair — Qin Pro

✓
2020 BYD Qin petrol. After front collision repairs, the airbags did not deploy but the SRS warning light stayed on in the instrument cluster. DTCs read: B16A5 and multiple collision sensor communication faults. The deceleration shock during the collision caused a checksum error in the SRS ECU internal memory, and the ECU entered protection mode. Repair process: Inspected ECU casing — no external damage, power supply normal. Attempted battery disconnect reset with no success. Used the BYD VDS diagnostic tool to execute ‘SRS system reconfiguration’, writing the correct vehicle configuration data and calibration parameters. After programming, cleared fault codes and performed the seat occupancy sensor and seatbelt buckle switch relearn procedures. Fault resolved.
BYD DTC AI Analysis

ECU internal corrosion after wading in Song MAX

✓
2019 Song MAX. After driving through heavy rain and floodwater, the airbag warning light came on. Disassembly inspection found the SRS ECU mounted beneath the floor. Although it had an external waterproof cover, the aged seal allowed water in. Opening the ECU housing showed obvious water stains and green corrosion on the PCB. Pins 12–15 of the main chip had corroded, creating an open circuit. DTCs B16A5 and B16A4 (internal fault) appeared simultaneously. Repair: Because the ECU is a safety-critical component and internal corrosion is irreversible, we replaced the SRS ECU assembly with a new unit. We also replaced the waterproof sealing ring, rerouted the wiring harness waterproof sleeve, and reinforced the mounting bracket with sealant. After replacement, we performed online programming and a system self-test. Normal function returned.
BYD DTC AI Analysis

Unauthorised inverter installation caused electromagnetic interference

✓
BYD Qin petrol ride-hailing car. The owner installed a 3000W vehicle inverter to power a food delivery insulated box. The airbag warning light flickered intermittently while driving. The scan tool retrieved an intermittent B16A5 DTC. Inspection found the inverter power cable connected directly to the battery without a filter, and routed close to the SRS ECU harness (in the centre console tunnel). High-frequency harmonics from the high-power inverter coupled into the ECU through the power lines, interfering with the internal ADC circuit and causing self-test anomalies. Removed the inverter, cleared the DTC, and road tested the vehicle continuously for 100 km with no recurrence. Advised the owner: if the inverter must be used, install a π-type filter at the power supply end and route the wiring at least 20 cm away from the SRS harness.
BYD DTC AI Analysis

Long-term parking caused EEPROM data loss

✓
2019 BYD Song MAX. Vehicle would not start after sitting in an underground garage for three months. SRS warning light stayed on after jump-start, stored DTC B16A5. Measured battery voltage: only 8.5 V, severely discharged. SRS ECU attempted multiple self-checks under low voltage, causing abnormal data to be written to the internal EEPROM. Software reflash failed; scan tool reported "internal memory access error". Diagnosed as internal ECU hardware damage (EEPROM chip failure). Replaced SRS ECU and battery (old battery damaged). Checked quiescent current (should be <50 mA); ruled out parasitic drain and delivered vehicle.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.