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B16A4-00

DTC B16A4-00 indicates the airbag control unit (SRS ECU) detects an internal or systemic fault — Qin Plus

Safety System

DTC B16A4-00 indicates the airbag control unit (SRS ECU) detects an internal or systemic fault.

As the core control module of the safety system, the SRS ECU monitors crash sensor status, controls the firing and deployment of airbags and seat belt pretensioners, and communicates with the vehicle CAN network.

This fault indicates potential hardware damage, software malfunction, or power/communication interruption in the ECU’s internal microprocessor, memory, power regulation circuit, or communication interface.

When this DTC triggers, the SRS system enters fail-safe mode.

All airbags (driver, passenger, side, and curtain) and seat belt pretensioners may fail to deploy during a collision.

The instrument cluster continuously illuminates the airbag warning light, severely compromising passive safety protection.

The B16A4-00 fault code on the Qin Plus indicates an internal fault in the airbag control unit (SRS ECU), triggering fail-safe mode where airbags and seat belt pretensioners may not deploy. Severity is medium. Common causes include internal hardware failure or abnormal power supply. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available based on 4 recorded cases.
4
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1SRS ECU internal hardware fault: Short or open circuit in the capacitors, resistors, processor chip, or ignition drive circuit on the control unit internal circuit board due to aging, overheating, or manufacturing defects.
  • 2Abnormal power supply: Unstable constant power (B+) or ignition power (IG) voltage (below 9V or above 16V), excessive contact resistance in the power supply circuit, blown fuse, or loose or corroded ground points G501/G502.
  • 3CAN bus communication fault: Short circuit between powertrain CAN or body CAN H and L lines, short to ground or power, open circuit, or abnormal terminating resistance prevents the ECU from communicating normally with the vehicle network.
  • 4Software/data fault: Corrupted internal ECU EEPROM data, incomplete program flashing, software version mismatch with hardware, or signal interference from vehicle modifications (such as installing aftermarket electronic equipment)
  • 5Physical damage or water ingress: Vehicle wading, liquid intrusion during interior cleaning, or collision damage causing ECU housing seal failure, resulting in internal circuit corrosion or cracked solder joints.
What To Do
  • 1
    Fault confirmation and freeze frame recording: Use a BYD VDS2000 or Launch X-431 diagnostic tool to read all DTCs. Record the freeze frame data (vehicle speed, voltage, and temperature at the time of the fault). Check for related fault codes (such as U0140-00 BCM communication fault and B16A5-00 internal fault).
  • 2
    Power and ground circuit inspection: Disconnect the negative battery terminal, wait 3 minutes, then unplug the SRS ECU connector. Measure the voltage from connector pin 1 (B+ constant power) to ground, and from pin 17 (IG power) to ground (should be 12V ± 0.5V). Measure the resistance between the ground pin (e.g., pin 34) and body ground (should be less than 1Ω). Check fuses SB03/SB08.
  • 3
    CAN communication circuit inspection: Turn the ignition ON. Measure the voltage at diagnostic connector pins 6 (CAN-H) and 14 (CAN-L) (normally around 2.5V; CAN-H slightly higher, CAN-L slightly lower). Use an oscilloscope to verify the waveform is a standard CAN signal (no noise, no flatline). Measure the resistance between the corresponding pins at the ECU connector (around 60Ω terminating resistance).
  • 4
    ECU appearance and connection inspection: Inspect the ECU mounting position (usually under the center console or inside the center armrest box) for water stains, corrosion, or impact damage. Verify the connector lock is intact and the terminals are not backed out or oxidized.
  • 5
    Software flash attempt: If circuit checks are normal, attempt an ECU software flash (SPS programming). Rewrite the ECU program using the latest software version. This resolves some faults caused by software bugs.
  • 6
    ECU replacement and matching: If the above steps fail, replace the SRS ECU with the same part number (e.g., 5A-3636100 series). Before installation, verify the vehicle VIN matches the old ECU data. After replacement, perform Online Matching, Coding, and crash sensor Calibration.
  • 7
    System verification: Clear the fault code and perform a system self-check (turn the ignition ON and verify the airbag warning light turns off after 6-8 seconds). Perform a simulated crash test (use the diagnostic tool to execute a crash output test and verify each circuit resistance is 2.0-3.0 Ω). Road test the vehicle to confirm the fault does not recur.
Real-World Cases
BYD DTC AI Analysis

Qin EV300: airbag warning light on, DTC B16A4-00 (Power Supply Voltage Abnormal) stored.

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Vehicle: 2017 Qin EV300, 80,000 km. Symptoms: Airbag warning light remained on after startup. Scan tool retrieved DTC B16A4-00. Diagnosis: Measured B+ voltage at SRS ECU connector at only 8.2V — low. Traced the cause to severe oxidation on the battery positive terminal. Also found the SB03 fuse (10A) base in the instrument panel distribution box burnt, causing poor contact. Repair: Cleaned and tightened battery terminals. Replaced the distribution box base and fuse. B+ voltage restored to 12.4V. Cleared fault codes and system returned to normal.
BYD DTC AI Analysis

Qin 100 SRS system failure after wading, DTC B16A4-00 (ECU water ingress corrosion).

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Vehicle: 2017 BYD Qin 100. Caught in heavy flooding with water above the door sills. Symptoms: After the vehicle dried out, the dashboard displayed "Check Airbag System" on startup. Scan tool retrieved DTC B16A4-00 and multiple crash sensor communication faults. Investigation: Removed the SRS ECU from beneath the centre console. Found the housing seal had perished, with clear water staining and pin corrosion on the internal circuit board. Repair: Fitted a new SRS ECU, cleaned and dried the wiring harness connectors, performed online coding and sensor calibration. Fault resolved.
BYD DTC AI Analysis

BYD Qin EV450 logged DTC B16A4-00 (CAN bus interference) following accident repairs

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Vehicle: 2018 BYD Qin EV450, after front-end collision repair. Symptom: After replacing the front bumper and wiring harness during the accident repair, the SRS warning light came on with code B16A4-00. Diagnosis: ECU power supply measured normal, but the oscilloscope detected significant noise on the CAN waveform. Inspection found the front compartment harness had chafed against the AC high-pressure line due to its routing during the repair, wearing through the CAN-H wire insulation and making intermittent contact with the metal pipe. Repair: Repaired the damaged CAN harness, rerouted and secured the wiring to avoid further interference. Cleared the fault codes; the system returned to normal.
BYD DTC AI Analysis

Qin 80 software version defect causing intermittent B16A4-00

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Vehicle: 2017 BYD Qin 80, 50,000 km. Symptoms: Intermittent airbag warning light illumination that cleared after cycling the ignition. Scan tool retrieved stored DTC B16A4-00. Troubleshooting: Checked power supply, ground and CAN bus wiring – all normal. ECU showed no physical damage. Consulted BYD technical service bulletin (TSB) and confirmed this production batch has an SRS ECU software bug that triggers false internal fault codes during specific voltage fluctuations. Repair: Performed ECU software upgrade using VDS (from V1.02 to V1.05). Monitored for one month after the upgrade with no recurrence.
Other Qin Plus 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.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.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 Qin Plus →Qin Plus 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.