AU
B16C3

DTC B16C3 indicates a functional fault in the airbag system electronic control unit (SRS_ECU) — Seal 6 EV

Safety System

DTC B16C3 indicates a functional fault in the airbag system electronic control unit (SRS_ECU).

The SRS_ECU is the core controller of the safety system.

It monitors crash sensor signals in real time, processes crash algorithms, controls the deployment timing of the airbags and seat belt pretensioners, and manages the communication network of the entire passive safety system.

This DTC usually indicates an internal processor or memory fault in the ECU, or a loss of communication between the ECU and the vehicle CAN network.

An intermittent open circuit in the ECU power supply or ground circuit can also trigger this fault.

This fault causes the airbag system to enter fail-safe mode.

The airbags may fail to deploy in a collision, creating a serious safety risk.

The B16C3 fault code on the Seal 6 EV indicates a medium-severity fault in the airbag system control unit. It may be caused by an internal ECU processor or memory problem, unstable power or ground supply, or a CAN bus communication fault. The system may enter fail-safe mode, so airbags may not deploy correctly in a crash. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
3
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Abnormal SRS ECU power supply circuit: Includes a blown constant power (B+) circuit fuse, poor relay contact, or unstable IGN supply voltage, causing ECU operating voltage to drop below 9V or exceed 16V.
  • 2CAN bus communication fault: Short circuit, open circuit, or abnormal terminal resistance in the communication line between the SRS_ECU and the vehicle network (powertrain CAN or dedicated safety CAN) prevents the ECU from communicating normally with the instrument cluster, VCU, and other modules.
  • 3ECU internal hardware damage: Control unit internal memory data corruption, abnormal processor clock, or collision detection circuit self-test failure, typically resulting from electromagnetic interference, overvoltage, or component aging.
  • 4Sensor circuit short circuit: A short to ground or power in the front impact sensor, side impact sensor, or clock spring wiring triggers the ECU protective shutdown function.
  • 5Software calibration error: Corrupted ECU internal calibration data, an incomplete flash update, or failure to perform online configuration (Coding) after parts replacement causes abnormal system recognition.
What To Do
  • 1
    Safety Preparation and Initial Diagnosis: Disconnect the high-voltage system (for new energy vehicles) and wait 5 minutes to allow capacitors to discharge. Use the BYD VDS diagnostic tool to read all fault codes. Confirm if B16C3 is a current (Active) fault and check for accompanying communication fault codes (such as the U01XX series). Record freeze frame data and note vehicle speed, voltage, and other parameters when the fault occurred.
  • 2
    Power supply and ground check: Check the SRS system fuses (F1/15, F2/13) in the front compartment distribution box to verify they are not blown. Disconnect the battery negative terminal, wait 90 seconds, and unplug the SRS ECU connector. Measure the voltage between pin 1 (constant power +B) and ground; the voltage must equal battery voltage. Measure the resistance between the ground pin and body ground; the resistance must be less than 1 Ω. Inspect the connector for oxidation or backed-out terminals.
  • 3
    Communication line inspection: Reconnect the battery and turn the ignition switch to ON (do not start). Use an oscilloscope to measure the waveforms at SRS ECU connector CAN-H (pin 6) and CAN-L (pin 14). The standard is a square-wave signal with CAN-H at 2.5-3.5V and CAN-L at 1.5-2.5V. If the voltage is abnormal (e.g., both are close to 0V or 12V), check the wiring harness for a short circuit or open circuit.
  • 4
    Sensor circuit troubleshooting: Inspect the wiring harness connectors for the front impact sensor (located on the longitudinal beam) and the side airbag sensor. Measure the sensor resistance to verify it is within the standard range (usually 2-3 kΩ). Check the steering wheel clock spring (spiral cable) continuity. Verify the driver-side airbag circuit resistance is normal (2-3 Ω) to rule out a sensor circuit fault causing an ECU misjudgment.
  • 5
    ECU replacement and calibration: If all wiring measurements are normal, update the SRS ECU software (if BYD has released a relevant upgrade package). If the fault remains, replace the SRS ECU. After replacement, use VDS to perform 'Online Coding' and 'Calibration', entering the correct vehicle VIN and safety configuration code. Finally, clear the fault codes, perform a system self-check (the indicator light should turn off), and perform a simulated crash test (using dedicated equipment) to verify system functionality.
Real-World Cases
BYD DTC AI Analysis

BYD Song MAX: Faulty evaporator temperature sensor caused air conditioning failure

✓
Poor A/C cooling, vent temperature not low enough, intermittent compressor operation. VDS scan found DTC B2A2F09 (evaporator temperature sensor fault). Data stream showed evaporator temperature fixed at –40°C (clearly abnormal). Further inspection revealed backed-out pins in the evaporator temperature sensor connector causing poor contact. Re-secured the sensor connector pins and cleared the fault code. Data stream returned to normal and A/C cooling function was restored.
Original source ↗
BYD DTC AI Analysis

BYD Qin DM: A/C compressor not starting

✓
After turning on the A/C, no cold air blew from the vents, the compressor did not start, and the recirculation/fresh air switching was inoperative. The owner initially ran an OBD scan and found multiple communication fault codes in the climate control system. Inspection at the dealership confirmed an abnormal power supply to the HVAC control module. The A/C compressor fuse in the engine bay fuse box had blown. Replacing the fuse did not fix the fault. Further investigation revealed an internal short circuit in the A/C pressure switch, triggering system protection. After replacing the pressure switch, the compressor worked normally and the fault was fully resolved.
Original source ↗
BYD DTC AI Analysis

BYD Song Pro automatic A/C temperature control fault

✓
The fault symptoms were a significant discrepancy between the set temperature and actual air outlet temperature, a noticeable temperature difference between the left and right air vents, and abnormal fan speed adjustment in AUTO mode. A dealership technician used a scan tool to retrieve fault codes related to the temperature blend door actuator. Checking the live data from each temperature sensor, the technician found the cabin temperature sensor reading deviated from the actual ambient temperature by about 15°C. The technician diagnosed a failed cabin temperature sensor (located inside the dashboard). The repair involved replacing the cabin temperature sensor and recalibrating the blend door actuator using the scan tool. After the repair, temperature control accuracy returned to normal.
Other Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.