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B16C1

DTC B16C1 indicates the airbag control unit (SRS ECU) detected an internal system fault or an external power supply or communication abnormality — Seal 6 EV

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 Seal 6 EV indicates a medium-severity fault in the airbag control unit, related to internal ECU checks, power supply, or CAN communication. Common causes include a weak or unstable 12V supply, blown airbag fuse, or poor power circuit connection. Because airbag deployment may be affected, the recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Low-voltage battery discharged or voltage unstable (long-term parking causes voltage to drop below 9V, or a charging system fault causes voltage to exceed 16V), exceeding the normal operating voltage range of the SRS ECU.
  • 2SRS ECU power supply circuit fault, including a blown dedicated airbag fuse (usually 10A or 15A) in the instrument panel power distribution box, a backed-out power supply pin, or a poor circuit connection causing excessive voltage drop.
  • 3Abnormal ECU ground circuit resistance. Oxidation, excessively thick paint, or loose fastening bolts at the front bulkhead or instrument panel crossmember ground point cause ground resistance to exceed 1Ω.
  • 4CAN bus communication fault: short circuit between CAN-H and CAN-L lines, short to power or ground, or abnormal terminating resistor (usually 120Ω) prevents the ECU from communicating with the vehicle gateway.
  • 5Internal hardware damage in the SRS ECU, including an aging internal step-down capacitor, cold solder joints on the main control chip (MCU), or memory data corruption (reflash calibration data or replace the ECU).
What To Do
  • 1
    Pre-inspection and voltage measurement: Check the vehicle low-voltage battery voltage. Standard value: 12.5-14.5V (ignition switch in the ON position). If the voltage is abnormal, rectify the battery or DC-DC fault first, clear the DTC, and repeat 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-class communication fault codes (such as U0100) or related codes such as B16C0/B16C2. Record the voltage values and mileage in the freeze frame to determine if the fault is historical.
  • 3
    Power and ground circuit inspection: Disconnect the negative battery terminal, wait 90 seconds for the capacitor to discharge, and unplug the SRS ECU connector (typically 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 (must be greater than 11V). Measure the resistance between the ground terminal and the body ground point (must be less than 1Ω).
  • 4
    CAN communication line 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), and measure the insulation to ground and power.
  • 5
    Wiring harness and connector inspection: Check the ECU connector for water ingress, corrosion, enlarged pin holes, or backed-out terminals. Check the wiring harness sleeve at the front bulkhead pass-through for damage. On accident-repaired vehicles, specifically check the 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 differ by model; Yuan EV and Tang units are not interchangeable). After replacement, perform online configuration (Coding) and airbag system calibration (Calibration). Some models require special equipment to write the VIN and configuration data.
  • 7
    System self-check and crash output test: After replacement, connect the diagnostic tool to clear the fault codes. Perform an ignition cycle self-check (turn IGN ON, wait 6 seconds, and verify 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 exist 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

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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 Seal 6 EV 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.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.B1109DTC B1109 indicates an open circuit in the communication line between the air conditioning system PM2.5 air quality sensor (dust concentration sensor) and the air conditioning control unit (AC ECU), or an open circuit within the sensor internal circuitry. Typically located in the air conditioning intake duct, this sensor monitors real-time PM2.5 particle concentration inside and outside the vehicle. It provides data to the automatic air conditioning system for intelligent switching between fresh air and recirculation modes and for controlling the air purification device. During an open circuit fault, the AC ECU cannot receive the air quality signal, triggering the system fail-safe mode. Symptoms typically include failure of the automatic recirculation function, abnormal air purification indicator light operation, or abnormal air quality data displayed on the air conditioning panel. Severe cases may compromise the cabin environment control strategy, but do not directly affect vehicle driving safety.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.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 Seal 6 EV →Seal 6 EV 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.