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B16A4

DTC B16A4 indicates the airbag control unit (SRS ECU) detected an internal system fault or critical support circuit abnormality — Qin Plus

Safety System

DTC B16A4 indicates the airbag control unit (SRS ECU) detected an internal system fault or critical support circuit abnormality.

As the core of the passive safety system, the ECU processes real-time data from the front and rear crash sensors, side pressure sensors, and accelerometers.

It determines airbag deployment, seat belt pretensioner activation, and high-voltage interlock disconnection.

This DTC triggers when the ECU self-diagnostic detects an internal CPU processing error, an EEPROM memory checksum failure, a transient voltage drop at the power supply monitoring circuit, or a communication interruption between the master and slave safety chips.

In this condition, the system enters fail-safe mode.

This mode may disable all airbag deployment functions and fails to guarantee normal protection logic during a collision, creating a severe safety hazard.

The B16A4 fault code on the Qin Plus indicates an internal fault in the airbag control unit (SRS ECU) or its support circuits. This medium severity issue may disable airbag deployment during a collision. Common causes include poor solder joints on the ECU circuit board or power supply faults. 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
  • 1Poor solder joint on the SRS ECU internal PCB or hardware fault in the main control chip (such as Infineon or Renesas series)
  • 2ECU power supply circuit fault: excessive resistance in the constant power (+B) circuit, poor contact at the ignition switch power supply (IG1), or corrosion at ground terminals G301/G302 causing voltage fluctuations.
  • 3CAN bus communication fault: Electromagnetic interference disrupts the power CAN or chassis CAN signal between the SRS ECU and the instrument cluster or VCU, or terminal resistor mismatch causes data frame loss.
  • 4Crash sensor internal short circuit: A short to ground or power in the front or side crash sensor signal harness triggers the ECU analog input port overload protection.
  • 5Internal ECU accelerometer damage from a previous collision, or ECU housing seal failure due to vehicle wading, resulting in internal circuit board oxidation and corrosion.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (ED400 or VDS) to read the complete DTC list. Check for accompanying B16A3 (SRS ECU internal fault), U0155 (lost communication with instrument cluster), or B1B00 series sensor fault codes. Record the freeze frame data.
  • 2
    Check battery voltage and body ground points. Measure voltage at SRS ECU connector terminal 1 (+B constant power) and terminal 9 (IG1 power). Verify static voltage is ≥12.4V and dynamic voltage is ≥9V. Verify ground circuit resistance is <1Ω.
  • 3
    Disconnect the battery negative terminal and wait 3 minutes (for capacitor discharge). Check the ECU connector (located under the center console or at the rear of the center armrest box) for pin oxidation, backed-out pins, or wiring harness wear. Clean with electrical contact cleaner if necessary.
  • 4
    Use an oscilloscope to measure CAN-H (2.5-3.5V) and CAN-L (1.5-2.5V) waveforms. Check for abnormal pulses or a short to power/ground, and verify network topology integrity.
  • 5
    Check the SRS ECU software version and compare it with the BYD TIS technical bulletin. If a newer software version is available (such as a patch for B16A4), upgrade the software and reconfigure the vehicle VIN and airbag parameters.
  • 6
    If the fault code persists, replace the SRS ECU assembly (select the part number based on the vehicle model, e.g., Yuan EV: EG-5820100). After replacement, perform: ① Coding ② Crash sensor calibration ③ System self-diagnostic test.
  • 7
    Use the diagnostic tool to perform the 'Airbag System Check' function and simulate a crash signal (without actual deployment). Confirm the system status returns to normal, clear the fault code, and verify with a road test.
Real-World Cases
BYD DTC AI Analysis

BYD Tang DM-i: Power fluctuation causes intermittent SRS ECU fault

✓
A 2021 Tang DM-i with 30,000 km on the clock showed an intermittent "Check SRS System" warning on the dash, with fault codes B16A4 and U0155 present. Diagnosis revealed an aftermarket dash cam drawing power from the SRS fuse circuit, causing voltage to drop to 8.2V on startup. Restored the factory power circuit, fitted a filter capacitor to the SRS ECU power supply, and upgraded the ECU software to V2.3 to improve voltage tolerance. Fault resolved.
BYD DTC AI Analysis

Flooded Yuan EV: SRS ECU Internal Corrosion Repair Case

✓
2019 Yuan EV logged DTC B16A4 after a water wading incident. Disassembly found the SRS ECU mounted under the floor. The internal PCB showed copper corrosion, and the accelerometer chip solder joints had cracked. Because the ECU is a safety-critical component and internally potted, it cannot be repaired; we fitted a new ECU. Recalibrated the zero points for the three collision sensors (left front, right front, centre) using the diagnostic scanner, and completed the high-voltage interlock loop check. Total labour time: 4.5 hours.
BYD DTC AI Analysis

CAN bus interference caused B16A4 fault in BYD Song MAX

✓
After the accident repair, the SRS warning light stayed on and stored DTC B16A4 along with multiple U communication faults. Inspection found the wiring harness was not secured properly during the repair, causing the SRS ECU CAN bus wiring to run parallel to the orange high-voltage wiring for an excessive distance. This caused electromagnetic coupling interference. Fix: re-routed the wiring to maintain ≥200 mm separation between the CAN lines and high-voltage cables, added a ferrite core at the ECU end, cleared the fault codes, and monitored the vehicle for 200 km with no recurrence.
BYD DTC AI Analysis

Failure to configure the instrument cluster after replacement caused an SRS fault on the Qin Pro EV

✓
Following instrument cluster replacement at a dealership, a 2020 Qin Pro EV set an SRS B16A4 fault with the airbag warning light remaining constantly on. Diagnosis revealed the replacement cluster lacked the correct security system configuration code, causing a failed security authentication handshake with the SRS ECU. Repair procedure: Using the VDS diagnostic tool, navigate to 'Special Functions - SRS Configuration', enter the correct configuration code (based on vehicle trim: 5-airbag or 6-airbag variant), and perform online matching to clear the fault.
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.