AU
B16FF12

DTC B16FF12 indicates a short to the vehicle 12V power supply on the fourth circuit (typically the signal or CAN communication line) of an SRS (airbag system) crash sensor (such as the front crash sensor, side crash sensor, or seat occupancy sensor) — Seal U

Safety System

DTC B16FF12 indicates a short to the vehicle 12V power supply on the fourth circuit (typically the signal or CAN communication line) of an SRS (airbag system) crash sensor (such as the front crash sensor, side crash sensor, or seat occupancy sensor).

In the BYD Qin PRO 4-wire sensor architecture, the fourth wire typically transmits sensor signals or diagnostic communications.

When this circuit shorts to power, the SRS control unit (ACM) detects an abnormal voltage (continuous high level) and fails to receive the sensor acceleration signal correctly.

This triggers the safety protection mechanism, forces the airbag system into fail-safe mode (system disabled), and illuminates the instrument cluster airbag warning lamp.

This fault may prevent proper airbag deployment during a collision, posing a severe safety hazard.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Wiring harness mechanical damage: Long-term vibration and chafing against sharp edges damage the engine compartment or door harness insulation, causing the fourth wire to short to a power wire (such as a constant 12V wire). This commonly occurs in harnesses passing through the firewall or hinges.
  • 2Connector water ingress and corrosion: Vehicle wading or poor sealing allows water to enter the sensor connector (usually located inside the front bumper or below the B-pillar), causing an electrolytic short circuit between the pins, specifically creating a conductive path between the fourth wire and the power supply pin.
  • 3Internal sensor fault: The signal processing chip or filter capacitor on the collision sensor internal PCB breaks down, shorting the signal output terminal (fourth wire) to the internal power supply terminal.
  • 4Improper repair work: During collision repair or aftermarket equipment installation (such as a dash cam or radar), mistakenly connecting the SRS sensor wiring harness in parallel with a power wire, or a retaining clip piercing the wiring harness insulation.
  • 5External electromagnetic interference damage: Although rare, extreme high-power electromagnetic interference can damage the sensor's internal circuitry, causing the output stage to short to power.
What To Do
  • 1
    Safety Preparation: Use the BYD VDS2000 or a dedicated diagnostic tool to read the fault code. Confirm B16FF12 is a current fault and the freeze frame data shows the vehicle status when the fault occurred. Disconnect the battery negative terminal and wait at least 3 minutes to fully discharge the SRS control unit capacitor and ensure repair safety.
  • 2
    Locate the faulty sensor: Refer to the Qin PRO workshop manual wiring diagram. Determine the exact sensor location (front left/front right crash sensor, side airbag sensor, or seat occupancy sensor) based on the DTC sub-code information, and verify the function of the fourth wire (usually the signal wire or CAN-L).
  • 3
    Sectional isolation test: Disconnect the sensor connector. Use a multimeter to measure the voltage between the fourth wire on the wiring harness side and body ground. A 12V reading confirms a wiring harness short to power. Measure the resistance between the fourth wire on the sensor side and the power pin. Continuity confirms an internal sensor short circuit.
  • 4
    Wiring harness inspection and repair: Inspect along the sensor wiring harness routing. Focus on the firewall pass-through, wiring harness retaining clips, and intersections with the front compartment wiring harness. If damaged, open the wiring harness, separate the shorted wires, and insulate them with heat-shrink tubing or electrical tape. Replace the entire wiring harness if necessary.
  • 5
    Connector handling: Inspect the connector pins for oxidation, deformation, or water marks. Clean with electrical contact cleaner, apply conductive grease, and replace the connector assembly if necessary. Verify the waterproof sealing ring is intact.
  • 6
    Sensor replacement: If diagnostics confirm an internal short circuit, replace with an OEM collision sensor (Note: Some models require sensor coding configuration or height calibration).
  • 7
    System verification: Restore all connections, connect the battery, and turn the ignition on. Use the diagnostic tool to clear the fault codes and perform the SRS system self-test (may include sensor communication tests and collision signal simulation). Verify DTC B16FF12 does not return and the instrument warning light is off.
Real-World Cases
BYD DTC AI Analysis

A worn front bumper wiring harness on a Qin Pro DM caused a short circuit.

✓
A 2019 Qin PRO DM with 30,000 km had the airbag warning light on the dash stay on constantly. Scanning revealed DTC B16FF12 (Right front impact sensor Line 4 short to power). The wiring harness retaining clip inside the right front wheel arch had come loose, allowing the harness to chafe against the edge of the engine mount bracket. The insulation wore through, and the Line 4 signal wire contacted the 12V power wire. Repairing the wiring and re-securing the harness cleared the fault.
BYD DTC AI Analysis

Sensor connector shorted due to water ingress during wading

✓
2018 BYD Qin Pro (petrol). Airbag warning light came on after driving through heavy rain and flood water, logging DTC B16FF12. Diagnosis found water ingress in the left front impact sensor connector (inside the left front chassis rail). Electrolyte formed between the pins, shorting the fourth wire to the power pin. Cleaned and blow-dried the connector, applied waterproof silicone grease, and replaced the seal ring – fault resolved. Check the wading depth sensor for watertightness.
BYD DTC AI Analysis

Wiring harness pinched during accident repair, causing short circuit

✓
A 2019 BYD Qin Pro developed DTC B16FF12 following accident repairs. Inspection found the wiring loom incorrectly trapped between the metal bracket and front bumper during the repair, crushing the insulation on the fourth wire and causing a short to the bracket (indirectly energised via a modified LED light wire). Rerouted the wiring loom away from the pinch point. Fault cleared.
BYD DTC AI Analysis

Internal PCB failure in the sensor

✓
2019 Qin Pro DM. Recurring B16FF12 DTC. Checked wiring harness, no abnormality found. Measured between pin 4 of the sensor connector and the power supply terminal; found internal short. Replaced left front impact sensor, fault resolved. Diagnosed as internal signal processing chip breakdown, likely due to early batch component defect or voltage surge.
Other Seal U 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.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.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
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.