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B16A3

DTC B16A3 indicates an internal fault in the airbag electronic control unit (SRS ECU, also known as the ACU - Airbag Control Module) — Atto 3

Safety System

DTC B16A3 indicates an internal fault in the airbag electronic control unit (SRS ECU, also known as the ACU - Airbag Control Module).

This fault points to an abnormality within the ECU processor, memory (EEPROM), power supply monitoring circuit, or safety sensor monitoring circuit, rather than an issue with external airbags, sensors, or wiring harnesses.

The ECU internal self-diagnostic program triggers this DTC when it detects key circuit parameters exceeding thresholds (e.g., internal voltage reference deviation, memory checksum failure, or watchdog reset).

This fault may prevent the airbag system from deploying normally during a collision or create a risk of unintended deployment.

It constitutes a core fault in the passive safety system and requires immediate resolution.

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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1SRS ECU internal memory damaged or data verification failed (crash algorithm parameters and configuration codes stored in the EEPROM lost or corrupted).
  • 2ECU internal power supply monitoring circuit fault (abnormal internal voltage regulator output causes the ECU to incorrectly determine its power supply status)
  • 3External power supply system fault (IG1 power supply voltage fluctuation or excessive ground point contact resistance, causing ECU internal low-voltage reset)
  • 4A vehicle collision or severe vibration damages the ECU internal acceleration sensor or locks the record (Crash Locked state), triggering an internal fault even without airbag deployment.
  • 5Defective ECU software/firmware version or flashing failure (interrupted upgrade causes configuration data loss on some models)
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal and wait at least 90 seconds to fully discharge the capacitors and prevent accidental airbag deployment; read and record all fault codes and freeze frame data.
  • 2
    Basic inspection: Check the SRS ECU exterior for physical damage or water ingress; check if fuse F1/15 (IG1 power supply) is intact; check ECU connectors G36/G37 for oxidation or backed-out pins.
  • 3
    Power supply and ground verification: Measure the voltage from G36-1 (IG1) to ground (should be 11-14 V); measure the resistance from G36-35 (GND) to body ground (should be <1 Ω); measure the resistance between the ECU housing and body ground (should be <1 Ω, ensuring good shield grounding).
  • 4
    Communication bus check: Measure CAN-H (G36-25) and CAN-L (G36-26) voltage to ground (should be 2.5-3.5V and 1.5-2.5V respectively); measure terminating resistance (approx. 60Ω); rule out ECU false faults caused by CAN communication interference.
  • 5
    Isolation test: Disconnect all airbag component and crash sensor connectors. Leave only the ECU power supply connected. Power on and read the fault code. If B16A3 remains, this confirms an internal ECU fault. If the code clears, reconnect the components one by one to locate the short circuit.
  • 6
    ECU replacement and configuration: Install a new SRS ECU. Use VDS or a dedicated diagnostic tool to: ① Write the VIN ② Match the vehicle configuration code (Option Code) ③ Calibrate the longitudinal/lateral acceleration sensor zero point ④ Perform a system self-check (verify no fault codes are present and the airbag warning light is off).
Real-World Cases
BYD DTC AI Analysis

BYD Qin SRS-ECU internal memory fault

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Symptoms: Airbag warning light constantly illuminated on the instrument cluster. DTC B16A3-00 stored. No collision history recorded. Diagnostic procedure: Measured ECU supply voltage at 12.4V – normal. Ground resistance 0.3Ω – normal. CAN bus communication showed no faults. Disconnected all airbag module connectors; the fault code remained. ECU showed no external damage, but internal EEPROM data verification failed (diagnostic tool showed ECU status code 0x01 error). Solution: Replaced the airbag control unit (ACU). Used VDS to write the VIN and perform sensor calibration. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Qin SRS multiple faults (B16A3+B1693+U0146)

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Symptoms: Intermittent airbag warning light while driving. DTCs retrieved with a scan tool: B16A3-00 (SRS ECU fault), B1693-00 (poor earth connection), U0146-00 (lost communication with gateway). Diagnostic process: Found the main body earth point G104 bolt loose. Tightened it — B1693 and U0146 cleared, but B16A3 remained. Further inspection showed insulating paint on the contact surface between the ECU housing mounting bracket and body, causing poor ECU housing earth (resistance >5Ω). Sanded the surface; fault code persisted. Determined the ECU internal power monitoring circuit had failed due to long-term poor earthing. Solution: Replaced the SRS ECU and ensured good housing earth. Fault completely resolved.
Original source ↗
BYD DTC AI Analysis

BYD Song MAX SRS ECU Configuration Lost Fault

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Symptoms: Airbag warning light on after servicing. DTCs B16A3-00 and B16A1-00 stored (ECU fault). Diagnosis: The vehicle had just received a gateway module software upgrade. Checked ECU power, ground, and communication – all normal. Scan tool showed internal ECU configuration data error (Checksum Error). Communication between the gateway and SRS ECU was interrupted during the upgrade, corrupting the ECU configuration parameters. Resolution: Reflashed SRS ECU firmware and restored configuration codes. Cleared DTCs after successful flash. System self-test passed. No hardware replacement required.
Original source ↗
BYD DTC AI Analysis

BYD Yuan EV ECU lockout fault after collision

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Symptoms: Vehicle had a low-speed collision (front bumper damaged, airbags did not deploy). Airbag warning light on. Read DTC B16A3-00. Diagnosis: Inspected front and rear impact sensors – no damage found. Wiring harness resistance normal. ECU power supply normal. Connected scan tool to view ECU internal status; 'Crash Locked' flag set. Internal accelerometer recorded the impact, triggering lockout protection mode. Fix: Per BYD workshop manual, ECU must be replaced once crash record locks. Fitted new ECU and performed system calibration. Fault cleared.
Original source ↗
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.