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B16A7

DTC B16A7 indicates the airbag control unit (SRS ECU) internal self-check detected a systemic fault — Qin Plus

Safety System

DTC B16A7 indicates the airbag control unit (SRS ECU) internal self-check detected a systemic fault.

This fault involves abnormalities in the SRS ECU internal microprocessor, memory (EEPROM/Flash), power management circuit, or watchdog circuit.

Specific causes include an internal 5V/3.3V reference voltage regulator fault, an acceleration sensor (Satellite Sensor) communication timeout, an internal algorithm self-check failure, or a non-volatile memory data checksum error.

Upon detecting this fault, the SRS ECU enters Fail-Safe Mode.

This mode may disable some or all airbag deployment and seat belt pretensioner activation functions, and illuminate the instrument cluster airbag warning light.

Because the airbag system is a critical passive safety system, this fault indicates the vehicle may fail to provide the designed occupant protection during a collision, creating a severe safety hazard.

The B16A7 fault code on the Qin Plus indicates an internal malfunction in the airbag control unit (SRS ECU), involving processor, memory, or power circuit failures. Severity is medium. Common causes include ECU hardware degradation from heat and humidity, or unstable battery voltage and poor grounding. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available based on 5 recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1SRS ECU internal hardware fault: Includes PCB capacitor aging and leakage, BGA chip cold solder joints, and internal acceleration sensor (MEMS) zero-point drift or damage. Common in vehicles operating in high-temperature, high-humidity environments.
  • 2Power supply system fault: unstable battery voltage (below 9V or above 16V); ground point oxidation causing excessive contact resistance; excessive voltage drop in the ignition switch power (IG1) circuit, especially voltage drop during startup triggering an ECU reset.
  • 3Wiring harness connector fault: SRS ECU 16-pin/24-pin connector terminals are recessed, backed out, oxidized, or exhibit water ingress (common after vehicle wading), causing abnormal power supply, ground, or CAN bus (HS-CAN) communication.
  • 4Software/calibration data corrupted: interrupted reflashing, battery power loss causing incomplete EEPROM data writing, software bug (early versions trigger false detection in low temperatures)
  • 5Electromagnetic interference or aftermarket equipment: Non-OEM dash cams, navigation devices, wireless chargers, and similar devices generate high-frequency interference to the SRS ECU through the power cables or CAN bus, causing the internal communication error rate to exceed limits.
What To Do
  • 1
    Use VDS2000 or a BYD dedicated diagnostic tool (such as ED400) to read the complete DTC list. Check for accompanying B16A5 (internal fault), U-prefix communication fault codes, or collision sensor-related faults. Record the freeze frame data.
  • 2
    Perform a key cycle test (Ignition ON 6 seconds → OFF 10 seconds → ON). Observe if the fault code is Current or History. Check if the instrument cluster airbag warning light remains illuminated or flashes a specific fault code.
  • 3
    Check the SRS ECU power supply system: Measure the voltage between connector terminal +B (constant power) and ground (standard: approximately 12.6 V). Measure IG1 (ignition power) to verify battery voltage with the ignition in the ON position. Check the tightening torque of ground points G301 and G302 (standard: 9-12 N·m).
  • 4
    Check the wiring harness connector: Disconnect the battery negative terminal for 3 minutes, then unplug the SRS ECU connector. Inspect the terminals for green oxidation, backed-out pins, or recessed pins. Measure the terminal retention force (must be ≥15N). Verify the connector sealing ring is intact. Apply Dielectric Grease if necessary.
  • 5
    CAN bus check: Measure resistance between CAN-H and CAN-L at the SRS ECU (standard: approx. 60 Ω; terminating resistor is in the instrument cluster or gateway) and voltage to ground (CAN-H: 2.5-3.5 V, CAN-L: 1.5-2.5 V) to rule out a bus short or open circuit.
  • 6
    Software reflash and configuration: If hardware inspection reveals no faults, reflash the SRS ECU using the latest software version (confirm the software version number applies to the vehicle model). After reflashing, perform coding and configuration. Input the correct vehicle VIN and airbag configuration parameters (such as whether side airbags, curtain airbags, etc., are equipped).
  • 7
    Replace the SRS ECU: If the above steps fail, replace the SRS ECU assembly. Note: Before replacement, disconnect the negative battery terminal and wait at least 3 minutes. After replacement, perform System Initialization and a self-check of all airbag circuits.
  • 8
    Final verification: Clear all DTCs and perform an on-vehicle collision simulation test (use the diagnostic tool to trigger a virtual collision signal without deploying actual airbags). Confirm the system operates normally and no fault codes return.
Real-World Cases
BYD DTC AI Analysis

Voltage drop at Tang DM-i startup instant causes intermittent B16A7 fault.

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Symptoms: 2021 BYD Tang DM-i with 30,000 km. Owner reported the airbag warning light occasionally illuminated during cold starts, automatically going out after driving for some time. Diagnosis: Connected the scan tool and retrieved stored DTC B16A7. Freeze frame data showed battery voltage at 8.1V when the fault occurred. Measured voltage during cranking and found it dropped to 7.8V with the starter motor engaged. Inspected the battery terminals and found negative earth point G301 corroded and loose. Repair: Removed the earth point, cleaned the contact surfaces with sandpaper, applied conductive grease, and tightened to the specified torque of 10 N·m. Replaced the aging battery. Fault resolved.
BYD DTC AI Analysis

Yuan EV SRS ECU connector corroded from water ingress after wading

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Symptoms: A 2019 Yuan EV developed DTCs B16A7 and B16A5 after driving through heavy flood water, with the airbag warning light staying on. Diagnosis: The vehicle had water reaching the floor level. The SRS ECU is mounted beneath the centre console. Upon removal, the 24-pin connector showed visible water ingress. Terminals A03 (ignition power) and A12 (earth) had green copper corrosion, and contact resistance measured 5.2 Ω (specification <0.1 Ω). Solution: Thoroughly cleaned the connector using electronic contact cleaner, replaced the damaged terminals, applied waterproof sealant, replaced the SRS ECU seal ring, and dried the components. The fault cleared.
BYD DTC AI Analysis

Outdated Song MAX software caused false low temperature detection.

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Symptoms: 2019 Song MAX, B16A7 fault appears frequently on winter morning startup, always appears when ambient temperature is below 5°C, clears once the vehicle warms up. Diagnosis: Checked power supply, earth, and wiring harness – all normal. Retrieved SRS ECU software version V1.02.03. Consulted Technical Service Bulletin (TSB) and confirmed this version has a bug with overly strict low-temperature self-test thresholds. Solution: Connected VDS2000, downloaded latest software V1.05.02, performed online programming reflash. After reflash, performed system configuration (selected correct airbag configuration level). Conducted low-temperature cold start testing for 3 consecutive days – fault did not return.
BYD DTC AI Analysis

Aftermarket dash cam on Qin Pro interfering with CAN bus

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Symptoms: 2020 Qin Pro petrol version. After the owner fitted a dashcam (tapped into constant +B power), the airbag warning light illuminated randomly while driving, logging DTC B16A7. Diagnosis: Disconnected the dashcam power and road-tested 50 km. The fault did not reoccur. Measurements revealed the dashcam power cable was generating high-frequency noise that coupled through the wiring to the SRS ECU, causing an increased bit error rate in the internal CAN transceiver and triggering the fail-safe mode. Solution: Removed the direct power connection, rewired the dashcam to the ACC relay (ignition-switched power), and added a ferrite core filter to the power lead. Fault resolved.
BYD DTC AI Analysis

Tang EV SRS ECU internal damage after accident repair

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Symptoms: 2021 Tang EV. After front collision repairs, the SRS warning light stays on constantly. DTC B16A7 is present and cannot be cleared. Diagnostic process: The shop replaced the front impact sensors and airbag module after the accident, but did not replace the SRS ECU—it looked undamaged. The ECU’s internal accelerometer output showed severe X-axis signal drift (should read 0g at rest; actual reading 0.8g). The collision impact had physically damaged the internal MEMS sensor. Solution: Replaced the SRS ECU with a new unit, performed online programming and coding (input vehicle VIN and configuration codes), and ran a comprehensive system self-test. All airbag circuit resistances read normally (2.0–3.0Ω). Fault resolved.
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.