AU
B16A7

DTC B16A7 indicates the airbag control unit (SRS ECU) internal self-check detected a systemic fault — Atto 3

Safety System

DTC B16A7 indicates the airbag control unit (SRS ECU) internal self-check detected a systemic fault.

This fault involves abnormalities in the SRS ECU internal microprocessor, memory (EEPROM/Flash), power management circuit, or watchdog circuit.

Specific causes include an internal 5V/3.3V reference voltage regulator fault, an acceleration sensor (Satellite Sensor) communication timeout, an internal algorithm self-check failure, or a non-volatile memory data checksum error.

Upon detecting this fault, the SRS ECU enters Fail-Safe Mode.

This mode may disable some or all airbag deployment and seat belt pretensioner activation functions, and illuminate the instrument cluster airbag warning light.

Because the airbag system is a critical passive safety system, this fault indicates the vehicle may fail to provide the designed occupant protection during a collision, creating a severe safety hazard.

The B16A7 fault code on the Atto 3 indicates an internal fault within the airbag control unit (SRS ECU), affecting its microprocessor, memory, or power circuits. Severity is medium. Common causes include internal hardware failure or power supply issues like unstable battery voltage. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available based on 5 recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1SRS ECU internal hardware fault: includes PCB capacitor aging and leakage, BGA chip cold solder joints, and internal acceleration sensor (MEMS) zero-point drift or damage. Common in vehicles operating in high-temperature, high-humidity environments.
  • 2Power supply system fault: unstable battery voltage (below 9V or above 16V), oxidized ground point causing excessive contact resistance, or excessive voltage drop in the ignition switch power (IG1) circuit, especially during startup, triggering an ECU reset.
  • 3Wiring harness connector fault: Recessed pins, backed-out pins, oxidation, or water ingress at the SRS ECU 16-pin/24-pin connector terminals (common after driving through water), causing abnormal power supply, ground, or CAN bus (HS-CAN) communication.
  • 4Corrupted software/calibration data: interrupted reflash process, battery power loss causing incomplete EEPROM data write, software version bug (early versions trigger false detections in low temperatures).
  • 5Electromagnetic interference or aftermarket accessories: Non-OEM dash cams, navigation devices, wireless chargers, or similar equipment introduce high-frequency interference to the SRS ECU via the power cables or CAN bus, causing the internal communication bit error rate to exceed limits.
What To Do
  • 1
    Use VDS2000 or a BYD dedicated diagnostic tool (such as ED400) to read the complete DTC list. Check for accompanying B16A5 (internal fault), U-series communication fault codes, or collision sensor-related faults. Record the freeze frame data.
  • 2
    Perform a key cycle test (Ignition ON 6 seconds → OFF 10 seconds → ON). Observe if the fault code is Current or History. Check if the instrument cluster airbag warning light remains illuminated or flashes a specific fault code.
  • 3
    Check the SRS ECU power supply system: Measure the voltage between connector terminal +B (constant power) and ground (standard: approximately 12.6V). Measure IG1 (ignition power) to verify battery voltage with the ignition in the ON position. Check the tightening torque of ground points G301 and G302 (standard: 9-12 N·m).
  • 4
    Check the wiring harness connector: Disconnect the battery negative terminal for 3 minutes, then unplug the SRS ECU connector. Inspect the terminals for green oxidation, backed-out pins, or recessed pins. Measure the terminal retention force (should be ≥15N). Verify the connector sealing ring is intact. Apply dielectric grease if necessary.
  • 5
    CAN bus check: Measure the resistance between CAN-H and CAN-L at the SRS ECU (standard: approx. 60Ω; terminating resistor is in the instrument cluster or gateway). Measure the voltage to ground (CAN-H: 2.5-3.5V, CAN-L: 1.5-2.5V) to rule out bus short or open circuits.
  • 6
    Software reflash and configuration: If the hardware inspection shows no faults, reflash the SRS ECU using the latest software version (verify the software version applies to the vehicle model). After completing the reflash, perform coding and configuration. Enter the correct vehicle VIN and airbag configuration parameters (such as the presence of side airbags, curtain airbags, etc.).
  • 7
    Replace the SRS ECU: If the above steps fail, replace the SRS ECU assembly. Note: Before replacement, disconnect the negative battery terminal and wait at least 3 minutes. After replacement, perform System Initialization and a self-check of all airbag circuits.
  • 8
    Final verification: Clear all DTCs, perform an on-vehicle crash simulation test (use the diagnostic tool to trigger a virtual crash signal without deploying the actual airbags), and confirm normal system operation and no recurring fault codes.
Real-World Cases
BYD DTC AI Analysis

Voltage drop at Tang DM-i startup instant causes intermittent B16A7 fault.

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Symptoms: 2021 BYD Tang DM-i with 30,000 km. Owner reported the airbag warning light occasionally illuminated during cold starts, automatically going out after driving for some time. Diagnosis: Connected the scan tool and retrieved stored DTC B16A7. Freeze frame data showed battery voltage at 8.1V when the fault occurred. Measured voltage during cranking and found it dropped to 7.8V with the starter motor engaged. Inspected the battery terminals and found negative earth point G301 corroded and loose. Repair: Removed the earth point, cleaned the contact surfaces with sandpaper, applied conductive grease, and tightened to the specified torque of 10 N·m. Replaced the aging battery. Fault resolved.
BYD DTC AI Analysis

Yuan EV SRS ECU connector corroded from water ingress after wading

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Symptoms: A 2019 Yuan EV developed DTCs B16A7 and B16A5 after driving through heavy flood water, with the airbag warning light staying on. Diagnosis: The vehicle had water reaching the floor level. The SRS ECU is mounted beneath the centre console. Upon removal, the 24-pin connector showed visible water ingress. Terminals A03 (ignition power) and A12 (earth) had green copper corrosion, and contact resistance measured 5.2 Ω (specification <0.1 Ω). Solution: Thoroughly cleaned the connector using electronic contact cleaner, replaced the damaged terminals, applied waterproof sealant, replaced the SRS ECU seal ring, and dried the components. The fault cleared.
BYD DTC AI Analysis

Outdated Song MAX software caused false low temperature detection.

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Symptoms: 2019 Song MAX, B16A7 fault appears frequently on winter morning startup, always appears when ambient temperature is below 5°C, clears once the vehicle warms up. Diagnosis: Checked power supply, earth, and wiring harness – all normal. Retrieved SRS ECU software version V1.02.03. Consulted Technical Service Bulletin (TSB) and confirmed this version has a bug with overly strict low-temperature self-test thresholds. Solution: Connected VDS2000, downloaded latest software V1.05.02, performed online programming reflash. After reflash, performed system configuration (selected correct airbag configuration level). Conducted low-temperature cold start testing for 3 consecutive days – fault did not return.
BYD DTC AI Analysis

Aftermarket dash cam on Qin Pro interfering with CAN bus

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Symptoms: 2020 Qin Pro petrol version. After the owner fitted a dashcam (tapped into constant +B power), the airbag warning light illuminated randomly while driving, logging DTC B16A7. Diagnosis: Disconnected the dashcam power and road-tested 50 km. The fault did not reoccur. Measurements revealed the dashcam power cable was generating high-frequency noise that coupled through the wiring to the SRS ECU, causing an increased bit error rate in the internal CAN transceiver and triggering the fail-safe mode. Solution: Removed the direct power connection, rewired the dashcam to the ACC relay (ignition-switched power), and added a ferrite core filter to the power lead. Fault resolved.
BYD DTC AI Analysis

Tang EV SRS ECU internal damage after accident repair

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Symptoms: 2021 Tang EV. After front collision repairs, the SRS warning light stays on constantly. DTC B16A7 is present and cannot be cleared. Diagnostic process: The shop replaced the front impact sensors and airbag module after the accident, but did not replace the SRS ECU—it looked undamaged. The ECU’s internal accelerometer output showed severe X-axis signal drift (should read 0g at rest; actual reading 0.8g). The collision impact had physically damaged the internal MEMS sensor. Solution: Replaced the SRS ECU with a new unit, performed online programming and coding (input vehicle VIN and configuration codes), and ran a comprehensive system self-test. All airbag circuit resistances read normally (2.0–3.0Ω). Fault resolved.
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.