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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) — Seal U

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
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal memory damaged or data verification failed (crash algorithm parameters and configuration codes stored in EEPROM lost or corrupted).
  • 2ECU internal power supply monitoring circuit fault (abnormal internal voltage regulator output causes the ECU to misjudge its own power supply status)
  • 3External power supply system fault (IG1 power supply voltage fluctuation or excessive ground point contact resistance causing an internal ECU low-voltage reset)
  • 4Vehicle collision or severe vibration damages the ECU internal acceleration sensor or locks the crash record (Crash Locked state), triggering an internal fault even if the airbags did not deploy.
  • 5ECU software/firmware version defect or flashing failure (an interrupted upgrade on some models causes configuration data loss)
What To Do
  • 1
    Safety preparation: Disconnect the 12V 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: Inspect the SRS ECU exterior for physical damage or water ingress; verify fuse F1/15 (IG1 power supply) is intact; inspect ECU connectors G36/G37 for oxidation or backed-out pins.
  • 3
    Power and ground verification: Measure the voltage from G36-1 (IG1) to ground (should be 11-14V); measure the resistance between G36-35 (GND) and body ground (should be <1Ω); measure the resistance between the ECU housing and body ground (should be <1Ω to ensure good shield grounding).
  • 4
    Communication bus check: Measure voltage to ground for CAN-H (G36-25) and CAN-L (G36-26) (expected: 2.5-3.5V and 1.5-2.5V respectively); measure terminating resistance (approximately 60Ω); rule out ECU false faults caused by CAN communication interference.
  • 5
    Isolation test: Disconnect all airbag and crash sensor connectors. Leave only the ECU power supply connected. Restore power and read the fault codes. If B16A3 remains, the ECU has an internal 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

✓
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

✓
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 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.