AU
B16FC12

DTC B16FC12 indicates the third wire of an SRS sensor (typically the signal or 5V reference wire) shorts to positive (B+ or 12V/5V supply) — Seal 6 EV

Safety System

DTC B16FC12 indicates the third wire of an SRS sensor (typically the signal or 5V reference wire) shorts to positive (B+ or 12V/5V supply).

In the BYD Qin PRO SRS architecture, crash sensors, seat occupancy sensors, and side airbag sensors typically use a three-wire design (power, ground, signal).

The "third wire" transmits the sensor status signal to the Airbag Control Unit (ACU) or receives the reference voltage.

When this circuit shorts to power, the ACU detects an abnormally high voltage (near battery voltage or above 5V) and determines the sensor signal is unreliable.

The ACU immediately illuminates the airbag warning light and sets the airbag system to fail-safe mode (deployment disabled).

This prevents unintended deployment or failure to deploy during a collision.

This fault compromises a core active safety function and requires immediate repair.

The B16FC12 fault code on the Seal 6 EV indicates a short to positive in the third wire of an SRS sensor circuit, often the signal or reference wire. Severity is high because the airbag warning light may turn on and the system can enter fail-safe mode, disabling deployment. Common causes include damaged wiring insulation near seats or under carpet, or an internal sensor short. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Worn harness insulation: Long-term vibration and chafing damage the sensor harness insulation where it passes through sheet metal holes, near seat slide rails, or under the carpet, causing a short circuit to a power wire (such as constant B+ or ignition power).
  • 2Internal sensor short circuit: Integrated circuit (IC) breakdown inside the crash sensor or seat occupancy sensor shorts the signal pin to the power supply pin, usually due to water ingress, electrostatic breakdown, or sensor aging.
  • 3Connector terminal short circuit: Metal debris, copper corrosion, or deformed terminals inside the sensor plug or ACU plug short the signal wire to the power terminal. This commonly occurs after driving through water or cleaning the interior.
  • 4Improper repair work: Failure to reinstall wiring harness retaining clips during previous repairs to the instrument panel, seats, or carpet allowed seat rails or sharp bracket edges to crush or cut the wiring harness, causing a short circuit to the body power supply wire.
  • 5Airbag Control Unit (ACU) internal fault: A power clamp diode breakdown or driver chip failure in the ACU internal signal processing circuit causes an abnormal reference voltage output to the sensor, registering as a short circuit fault.
What To Do
  • 1
    Use the BYD VDS2000/VDS3000 diagnostic tool to read the complete fault code stream. Confirm if B16FC12 is a Current DTC and check the freeze frame data. Record the vehicle status when the fault occurred (vehicle speed, timestamp). Use the diagnostic tool to identify the specific sensor location indicated (e.g., 'driver-side airbag sensor' or 'seat occupancy sensor').
  • 2
    Disconnect the negative battery cable and wait at least 90 seconds (to fully discharge the SRS backup power supply and comply with airbag repair safety standards). Refer to the wiring diagram in the corresponding model's repair manual to confirm the specific function of the faulty sensor's third wire (usually the signal wire Sig or 5V Ref).
  • 3
    Locate the faulty sensor (depending on vehicle model, this may be the seat occupancy sensor, side impact sensor, or front impact sensor). Disconnect the sensor connector and the ACU connector. Use a multimeter to measure continuity from the third wire to body ground and to power (B+) to determine whether the short circuit is in the wiring harness or the sensor.
  • 4
    If the wiring harness shows continuity to power: Visually inspect the harness along its routing for wear or burn marks. Focus on the harness under the seat, inside the B-pillar trim panel, and inside the door sill trim panel. Repair damaged sections using electrical tape or heat-shrink tubing. Replace the entire harness if necessary.
  • 5
    If the wiring harness insulation is normal: Measure the resistance between the third wire at the sensor connector and the power supply pin. If the resistance is less than 1Ω, this indicates an internal sensor short circuit. Replace the corresponding sensor (Note: Some sensors require zero-point calibration or coding).
  • 6
    Reconnect all connectors and connect the battery. Turn the ignition switch to the ON position. Use the diagnostic tool to clear the fault code and perform the 'SRS system self-check' procedure. Confirm B16FC12 does not reappear. Verify the instrument cluster airbag warning light turns off after the self-check.
  • 7
    Perform a road test to verify the repair. Simulate different operating conditions (bumpy roads, seat adjustment) and confirm the fault does not recur. Finally, use the diagnostic tool to read history fault codes and verify no new related faults exist.
Real-World Cases
BYD DTC AI Analysis

Qin PRO DM seat occupancy sensor wiring harness worn through, causing a short circuit

✓
A 2019 Qin PRO DM with 32,000 km displayed a "Please check SRS system" warning on the instrument cluster. Fault code B16FC12 was stored (driver's seat occupancy sensor line 3 short to power). Inspection found the wiring harness under the seat had chafed at the slide rail mounting bracket; the damaged insulation allowed the signal wire (yellow/red) to contact the seat heating constant power wire. The harness was repaired, rerouted and resecured, clearing the fault. Root cause: Long-term driving on rough roads loosened the harness retaining clips, causing the harness to rub against the metal bracket.
BYD DTC AI Analysis

Water ingress corroded the side impact sensor, causing an intermittent short circuit.

✓
2018 BYD Qin Pro (petrol), intermittent airbag warning light, DTC B16FC12 (left B-pillar side impact sensor). Removed the left B-pillar trim and found oxidation on the sensor connector; green copper corrosion between pin 3 (signal) and pin 1 (power) causing unstable resistance. Traced the root cause to a perished window seal allowing rainwater into the B-pillar. Cleaned the terminals, sprayed electronic contact cleaner, and replaced the seal. The fault has not reoccurred.
BYD DTC AI Analysis

Wiring harness crushed after accident repair, causing continuous short circuit

✓
A Qin PRO DM that had undergone accident repairs set a B16FC12 fault code after the front seats and carpet were replaced. Inspection found the technician had failed to clip the seat occupancy sensor harness into the wiring channel properly, and the seat rail fixing bolt pinched it. The damaged insulation shorted to the bolt (connected to the body’s positive power circuit). We rerouted the harness and secured it with genuine harness clips; fault cleared. When repairing accident damage, pay special attention to SRS harness routing and securing.
BYD DTC AI Analysis

Seat occupancy sensor internal IC breakdown fault

✓
2019 BYD Qin PRO DM. DTC B16FC12 stored and could not be cleared. Measured resistance at the seat occupancy sensor connector (pressure sensor type): only 0.3 Ω between the third wire (signal) and the power wire. Disconnected the sensor; the harness side measured normal, indicating an internal short in the sensor. Replaced the seat occupancy sensor (part number: S6DM-3638XXXX). Performed the 'seat sensor calibration' procedure with VDS. Fault resolved.
BYD DTC AI Analysis

Aftermarket seat heater install: signal wire misconnected to power.

✓
A 2018 BYD Qin Pro petrol model's SRS warning light came on after the owner had seat heating pads installed at an unauthorised workshop. DTC B16FC12 pointed to the passenger seat occupancy sensor. Inspection found the installer had spliced the heater power wire into the sensor signal wire, mistaking it for a power wire, which subjected the sensor signal line to continuous 12V. After removing the unauthorised wiring, restoring the factory harness connections, and replacing the damaged sensor, the system returned to normal.
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.