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B16C2-00

DTC B16C2-00 indicates the airbag control unit (SRS ECU) detected a critical fault during its internal self-check, forcing the system into fail-safe mode — Atto 3

Safety System

DTC B16C2-00 indicates the airbag control unit (SRS ECU) detected a critical fault during its internal self-check, forcing the system into fail-safe mode.

This fault involves a hardware-level abnormality in the ECU internal microprocessor, non-volatile memory (NVM), power management module, or safety monitoring circuit.

The ECU sets this code upon detecting an internal watchdog reset, checksum verification failure, integrated acceleration sensor (MEMS) signal processing circuit abnormality, or safety communication interruption between the main and secondary CPUs.

In BYD Qin series vehicles, this fault prevents the entire airbag system (including driver/passenger front airbags, side airbags, curtain airbags, and seat belt pretensioners) from deploying.

It may also interrupt communication with the powertrain CAN and body CAN, causing the instrument cluster to illuminate the airbag warning lamp continuously.

Unlike sensor or ignition circuit faults, this DTC indicates a functional failure of the ECU itself.

Inspect the ECU installation environment (the area beneath the center tunnel is susceptible to water ingress) and verify power supply stability.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1ECU internal hardware damage: main control chip (Renesas RH850 or Infineon TriCore safety-grade MCU) damage, EEPROM data block corruption, internal accelerometer (usually a Bosch or STMicroelectronics MEMS chip) component failure, or cold solder joints.
  • 2Abnormal power supply: blown constant power (B+) circuit fuse F1/14 (dedicated to Qin series SRS); unstable ignition switch power (IG1) voltage (below 9V or above 16V); internal ECU DC-DC converter module failure causing 5V/3.3V reference voltage drift.
  • 3Ground system fault: Loose or oxidized ECU main ground point G101 (located on the instrument panel frame) or broken ground wiring harness causes reference potential drift, affecting analog signal sampling accuracy.
  • 4CAN bus communication fault: Powertrain CAN (HS-CAN) or dedicated SRS-CAN wiring shorted to ground or power; short between CAN-H and CAN-L due to insulation damage; terminal resistor (120Ω) drift or absence causing signal reflection.
  • 5Abnormal software/calibration data: Uncleared crash data latch after a vehicle collision, loss of calibration data (Coding) due to electromagnetic interference, or software version mismatch with hardware Revision. Reflash or replace the ECU.
What To Do
  • 1
    Safety preparation and initial inspection: Disconnect the 12V battery negative terminal and wait at least 90 seconds (to fully discharge the ECU backup power supply). Use VDS2000 or the latest version of the diagnostic tool to read the complete fault codes and freeze frame data. Check the ECU housing for physical damage, water stains, burn marks, or signs of impact.
  • 2
    Wiring harness connector inspection: Inspect the terminals of ECU wiring harness connectors C1 (power/ground), C2 (CAN communication), and C3 (sensor/ignition circuit) for backed-out pins, corrosion, oxidation, or green corrosion. Specifically check for signs of water ingress under the center tunnel.
  • 3
    Power and ground test: Reconnect the battery (do not start the vehicle). Measure the voltage between ECU connector terminal 30 (constant power) and ground (should be 12.4-12.6V). Measure the voltage at terminal 15 (IGN) with the ignition in the ON position. Measure the resistance between the ground terminal and body ground (should be <0.5Ω). Check fuse continuity and fuse base contact resistance.
  • 4
    Communication line inspection: Disconnect the ECU connector. Measure the resistance between CAN-H (usually terminal 7) and CAN-L (usually terminal 8) (expected: approximately 60Ω, reflecting two 120Ω terminating resistors in parallel). Measure the insulation resistance to ground and to power (expected: >1MΩ). Check CAN line continuity between the OBD diagnostic port and the ECU.
  • 5
    Deep diagnostic scan: Connect the diagnostic tool and execute the 'SRS system self-test' to check for sub-fault codes (such as sub-codes B16C2-01 to B16C2-99). Read the integrated acceleration sensor live data stream (static X/Y-axis values should be 0±0.5g; Z-axis should be 1±0.1g). Check the watchdog counter and power supply voltage monitoring values.
  • 6
    Software repair attempt: If all hardware tests are normal, perform an "ECU software flash" (use the latest calibration file from the BYD after-sales server; the version must be higher than the current version). For vehicles with no collision but a false code, perform a "Crash Data Reset". This operation requires manufacturer authorization.
  • 7
    Replacement and Online Configuration: If the previous steps fail, replace the SRS ECU with the same part number (Qin 100/EV300: K2J-5823000-00; Qin EV450: K2J-5823000-01). After installation, perform 'Online Coding' to write the VIN, vehicle model code, and airbag configuration parameters (such as side curtain and knee airbags). Finally, perform 'System Configuration Verification' and a 'Vehicle Collision Simulation Test' (use a dedicated resistor load in place of the airbag).
Real-World Cases
BYD DTC AI Analysis

Intermittent SRS ECU fault on BYD Qin EV300 after wading

✓
A 2017 Qin EV300 developed an intermittent airbag light after driving through flood water during heavy rain. Retrieved DTCs: B16C2-00 (current) and U0151 (historical). Inspection found the SRS ECU mounted under the centre tunnel; the housing seal had aged and allowed water ingress, causing verdigris corrosion on the internal PCB. Measured the ECU's internal 5V reference: it dropped to 4.2V hot, starving the acceleration sensor of power. Fix: Replaced the SRS ECU (K2J-5823000-00), resealed the mounting location, added a waterproof gasket beneath the ECU, and performed online configuration. Fault resolved.
BYD DTC AI Analysis

Aftermarket stereo installation on a Qin 100 caused CAN bus interference, triggering an ECU fault.

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The owner reported that after installing an aftermarket touchscreen head unit, the airbag warning light stayed on. DTC B16C2-00 was stored, accompanied by multiple U-class communication faults. Technicians found the installation shop had bridged the SRS-CAN and infotainment CAN when tapping the head unit into the bus, causing signal reflection and abnormal voltage (CAN-H reached 4.8V). They removed the improper wiring, restored the factory CAN topology, and cleared the fault codes. The ECU then passed self-diagnosis. Recommendation: Never connect aftermarket devices to the SRS-CAN bus.
BYD DTC AI Analysis

Qin EV450 lost calibration data after collision repair

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After a frontal collision, the repair shop replaced the front airbags and impact sensors but did not replace the SRS ECU, as it appeared undamaged externally. After reassembly, the vehicle set code B16C2-00, and the scan tool displayed “Internal Configuration Error”. The ECU had latched collision data during the impact and entered fuse-locked mode, with partial calibration data corruption. Since BYD policy does not support unlocking, the shop replaced the ECU with a new unit. Using VDS, they performed “Online Configuration” to write the VIN and configuration codes (requires connection to the BYD server for authorisation). After completion, the system self-test passed.
BYD DTC AI Analysis

Unstable supply voltage caused ECU reset fault

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A BYD Qin 80 with 80,000 km had the airbag warning light illuminate at startup. DTC B16C2-00 was intermittent. Inspection found the battery had aged (increased internal resistance). Voltage dropped to 8.5 V during cranking, triggering the ECU internal undervoltage protection and setting the fault code. The ECU constant power terminal also had a poor connection — resistance measured 2.3 Ω (normal <0.1 Ω). Solution: replaced the battery, repaired the ECU power plug terminals (cleaned and fitted a locking tab), cleared the DTC. Followed up for one week, no recurrence.
BYD DTC AI Analysis

False positive caused by software version bug

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Some 2018-batch Qin EV450 vehicles have an ECU software calibration defect. When starting in extreme cold (below -15°C), a timing error in the internal self-diagnostic program falsely triggers B16C2-00. The vehicle has no actual hardware fault. After warm-up, you can clear the code, but it will return. Solution: Use VDS to perform a 'software upgrade' and flash the V2.3.1 calibration file (which fixes the low-temperature self-diagnostic timing). Flashing completely eliminated the fault. This shows that not all B16C2-00 codes require hardware replacement.
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.