AU
B16C1

DTC B16C1 indicates the airbag control unit (SRS ECU) detected an internal system fault or an external power supply or communication abnormality — Qin Plus

Safety System

DTC B16C1 indicates the airbag control unit (SRS ECU) detected an internal system fault or an external power supply or communication abnormality.

Specifically, this code points to a functional failure in the ECU power management module, internal memory (EEPROM/Flash) self-check, watchdog timer, or main processor.

The SRS ECU triggers this fault code and illuminates the airbag warning lamp if it detects an operating voltage outside the 9-16V range, an internal data verification failure, or a loss of communication with the vehicle CAN network during the ignition cycle self-check.

This fault forces the airbag system into a degraded mode.

During a collision, the system may fail to deploy the airbags or actuate the seatbelt pretensioners, posing a severe safety hazard.

The B16C1 fault code on the Qin Plus indicates an internal SRS ECU fault or abnormal power/communication signal affecting the airbag system. Severity is medium, but it can reduce airbag or seatbelt pretensioner function in a crash. Common causes include a weak or unstable battery, charging voltage outside range, or a faulty SRS power supply circuit or fuse. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Low-voltage battery depleted or voltage unstable (long-term parking causes voltage to drop below 9V, or a charging system fault causes voltage to exceed 16V), exceeding the SRS ECU normal operating voltage range.
  • 2SRS ECU power supply circuit fault, including a blown dedicated airbag fuse in the instrument panel power distribution box (usually 10A or 15A), a backed-out power supply pin, or a poor circuit connection causing excessive voltage drop.
  • 3Abnormal ECU ground circuit resistance. The ground point is on the front bulkhead or instrument panel crossmember. Oxidation, excessively thick paint, or loose fastening bolts cause ground resistance to exceed 1Ω.
  • 4CAN bus communication fault: Short circuit between CAN-H and CAN-L lines, short to power/ground, or abnormal terminating resistor (usually 120Ω) prevents ECU communication with the vehicle gateway.
  • 5Internal hardware damage to the SRS ECU, including aging internal step-down capacitor, cold solder joints on the main control chip (MCU), or corrupted memory data (requires reflashing calibration data or replacing the ECU)
What To Do
  • 1
    Pre-check and voltage measurement: Check the vehicle low-voltage battery voltage. The standard value is 12.5-14.5V (ignition switch ON). If the voltage is abnormal, repair the battery or DC-DC fault first, clear the DTC, and re-run the self-check.
  • 2
    Fault code reading and freeze frame analysis: Use VDS or a Launch diagnostic tool to read all DTCs. Check for accompanying U-series communication fault codes (such as U0100) or related codes like B16C0/B16C2. Record the freeze frame voltage values and mileage to determine if the fault is historical.
  • 3
    Power supply and ground circuit check: Disconnect the battery negative terminal, wait 90 seconds for the capacitor to discharge, then unplug the SRS ECU connector (usually a 39-pin or 54-pin black connector). Measure the voltage between connector terminal 1 (constant power B+) and body ground, and between terminal 2 (ignition switch power IG) and body ground (should be greater than 11V). Measure the resistance between the ground terminal and the body ground point (should be less than 1Ω).
  • 4
    CAN communication circuit inspection: Use an oscilloscope or multimeter to measure the resistance between CAN-H (orange/black) and CAN-L (orange/brown) at the SRS ECU connector (approximately 60Ω, two 120Ω terminating resistors in parallel), as well as insulation to ground and power supply.
  • 5
    Wiring harness and connector inspection: Inspect the ECU connector for water ingress, corrosion, enlarged pin holes, or backed-out pins. Inspect the wiring harness sleeve at the front bulkhead pass-through hole for damage. On accident-repaired vehicles, specifically check the wiring harness for crushing or cuts.
  • 6
    Replacement verification and calibration: If all circuit measurements are normal, replace the SRS ECU with one of the same part number (Note: BYD ECU part numbers vary by model; do not interchange Yuan EV and Tang units). After replacement, perform online configuration (Coding) and airbag system calibration (Calibration). On some models, use special equipment to write the VIN and configuration data.
  • 7
    System self-check and crash output test: After replacement, connect the diagnostic tool and clear the fault codes. Perform an ignition cycle self-check (turn IGN ON, wait 6 seconds, and observe if the airbag warning lamp turns off). Perform the passive safety system function test (use a dedicated resistor substitute; never directly measure the airbag inflator squib resistance). Confirm no fault codes remain before returning the vehicle.
Real-World Cases
BYD DTC AI Analysis

2019 BYD Song MAX: Flat battery caused intermittent B16C1 fault

✓
After sitting for 5 days, the vehicle displayed 'Check SRS System' on startup. Retrieved DTC B16C1. Battery voltage measured only 10.8V – discharged from sitting. Charged the battery to 12.6V, cleared the code, and the fault temporarily disappeared. Returned a week later. Measured static current draw at 180mA (should be under 50mA). Traced to parasitic drain from an aftermarket dashcam wired to constant power. Replaced the battery and fixed the drain; fault permanently resolved.
BYD DTC AI Analysis

2021 Tang: Poor SRS ECU grounding caused false system warnings

✓
The airbag warning light illuminated intermittently when driving on rough roads. Scanned the system and retrieved current DTC B16C1. Found the SRS ECU ground bolt (M6) loose at the dashboard crossmember. Improper cleaning left paint residue on the ground point, resulting in a measured resistance of 4.2Ω. Sanded the ground point to bare metal, applied conductive paste, and tightened the bolt to the specified torque (8-10 N·m). Ground resistance dropped to 0.3Ω. Road tested for 20 km with no fault recurrence. Returned vehicle to customer; no further issues after three months of use.
BYD DTC AI Analysis

2019 Yuan EV: B16C1 and U0151 present after accident repair

✓
After front collision repairs, the airbag warning light stayed on. DTCs read: B16C1 (SRS ECU fault) and U0151 (lost communication with airbag control unit). Inspection found the replacement bulkhead harness fitted during the collision repairs had terminals inside the new SRS ECU plug (39-pin) that weren't fully seated, causing poor contact on the CAN-H line (orange/black). Reseated the terminals, applied waterproof sealant, then performed 'Airbag System Configuration' and 'Collision Output Reset' using VDS. The DTCs cleared and the airbag light went out.
BYD DTC AI Analysis

BYD Qin Pro Petrol: SRS ECU Internal Failure Replacement Case

✓
While driving normally, an alarm went off and the airbag warning light stayed on. Could not clear DTC B16C1. Checked power, ground, and CAN lines — all normal. Measured ECU connector voltage: 12.4V; ground resistance: 0.5Ω; CAN waveform normal. Diagnosed an internal hardware fault in the SRS ECU. Replaced the ECU with a new unit (part no. BYD-3638100-XS2). Using the dedicated diagnostic tool, performed 'online configuration' (entered vehicle VIN to auto-download configuration data) and 'sensor calibration'. Then ran a simulated crash test (using a 2Ω resistor in place of the airbag). System worked normally, fault resolved.
BYD DTC AI Analysis

Yuan Pro 2021 — Outdated software version causes false alarm

✓
500 km after delivery, the SRS warning light came on, storing DTC B16C1. Checked wiring, no abnormalities found; voltage normal. Replacing the SRS ECU had no effect. Looked up BYD TSB-2021-SRS-03 and found that SRS ECU software version V1.02 in this production batch contains a bug—falsely reports internal faults under specific voltage fluctuations. Upgraded ECU software to V1.05 using VDS, with a backup battery connected to keep vehicle power stable. Cleared fault codes after the upgrade. Followed up for one month, 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.