AU
B16DF

DTC B16DF indicates the SRS (Supplemental Restraint System) ECU detects a communication interruption or physical disconnection of the Left Rear Impact Sensor — Seal U

Safety System

DTC B16DF indicates the SRS (Supplemental Restraint System) ECU detects a communication interruption or physical disconnection of the Left Rear Impact Sensor.

This sensor typically mounts in the vehicle's left rear quarter panel, C-pillar, or rear longitudinal beam area to monitor collision acceleration from the left rear.

The ECU sets this fault code if it fails to receive a valid signal (including the sensor ID code, acceleration data, or heartbeat signal) within the preset monitoring period, or if it detects circuit resistance outside the normal range (typically greater than 10 kΩ or less than 1 Ω).

This fault disables the left rear collision detection function.

During a side impact or rear-end collision, the SRS ECU may fail to accurately assess collision severity, compromising the deployment strategy of the side airbags, curtain airbags, or seat belt pretensioners and posing a severe safety risk.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Loose or disconnected wiring harness connector: After accident repairs, interior trim removal/installation, or water ingress, the sensor connector located inside the left rear door sill trim panel (usually a 3-pin or 2-pin waterproof plug) fails to lock fully, causing poor contact or complete disconnection.
  • 2Sensor harness open or short circuit: Long-term vibration wears through the harness insulation where routed through body panel holes, past seat slide rails, or under door sill trims. Rodents gnawing the wiring can also cause an open circuit or a short to the vehicle body.
  • 3Crash sensor internal fault: Damaged internal accelerometer element, capacitor leakage, or ASIC chip fault prevents the sensor from sending valid data frames to the SRS ECU.
  • 4SRS ECU interface fault: The corresponding sensor interface circuit inside the airbag control module (usually the PSI5 or DSI bus communication chip) is damaged and cannot interpret the sensor signal.
  • 5Sensor mounting bracket deformation: A minor rear impact deforms the sensor mounting base, causing poor grounding between the sensor and the vehicle body or physical damage to the connector.
What To Do
  • 1
    Safety preparation: Disconnect the low-voltage battery negative terminal and wait at least 90 seconds to allow the SRS capacitor to fully discharge. Read and record all DTCs and freeze frame data. Confirm B16DF is a current fault, not a history fault.
  • 2
    Physical inspection: Remove the left rear sill trim, lower C-pillar trim, or left side of the rear bumper. Visually verify the crash sensor connector (part number usually starts with 69C) is fully inserted and listen for a locking 'click'. Check the connector terminals for backed-out pins, corrosion, or signs of water ingress (green oxidation).
  • 3
    Circuit measurement: Disconnect the sensor and SRS ECU connectors. Use a multimeter to measure harness continuity. Sensor power supply wire (usually 12V or 5V) resistance to ground must exceed 1MΩ. Test the signal wire (PSI5 bus) for shorts to ground and power. Measure the circuit resistance between the sensor and ECU; resistance must be less than 1.5Ω.
  • 4
    Sensor test: Use an oscilloscope to measure the waveform on the sensor signal wire. A normal waveform shows a PSI5 protocol digital signal (current modulation, approximately 10-40mA swing). If the power supply is normal but the sensor outputs no signal, replace the left rear crash sensor (Note: Pair the new sensor with the ECU or allow it to auto-configure).
  • 5
    System reset and verification: Reconnect all connectors, reconnect the battery, and use the diagnostic tool to clear the fault codes. Check the sensor live data stream to confirm the left rear crash sensor status displays 'Normal' and the acceleration value changes accordingly when lightly tapping the vehicle body. Perform the SRS system self-test and confirm B16DF does not return.
Real-World Cases
BYD DTC AI Analysis

Loose connector after accident repairs caused B16DF

✓
Following left rear door accident repairs, a 2021 BYD Tang DM displayed a constant airbag warning light on the instrument cluster. Retrieved DTC B16DF (current). Inspection revealed that after the left rear C-pillar trim panel was removed and refitted, the impact sensor's grey connector was not fully seated and the locking tab was not engaged. Reseated the connector, confirmed the lock was engaged, then cleared the DTC. The warning light extinguished and live data showed normal sensor communication.
BYD DTC AI Analysis

Wiring harness wear causing intermittent B16DF fault

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2019 BYD Song MAX: Airbag warning light intermittently illuminated when driving on rough roads. Scan tool showed DTC B16DF as an intermittent fault. Inspected the left rear sill wiring harness and found the insulation chafed through at the retaining clip, with copper strands partially fractured causing poor contact. Repaired the harness by cutting out the damaged section, soldering the wires and insulating with heat shrink tubing. Rerouted and secured the harness to prevent contact with bodywork. Fault resolved.
BYD DTC AI Analysis

Sensor Internal Fault Replacement Case

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2020 BYD Qin Pro EV logged B16DF DTC after extended parking. Checked connectors were secure, measured 12V sensor supply as normal, and found no shorts or opens in signal lines. Used oscilloscope and found no current modulation signal from the sensor. Replaced left rear collision sensor (part number: 69C-XXXXX), installing with the arrow pointing toward the front of the vehicle. Cleared the DTC and system returned to normal.
BYD DTC AI Analysis

Sensor connector corroded after wading

✓
After wading through water, the airbag warning light came on in a 2019 BYD Yuan EV. Diagnosis found DTC B16DF. Disassembly revealed water inside the left rear sill. The impact sensor connector terminals showed obvious electrochemical corrosion (green copper rust). Cleaned the ECU pins and wiring harness terminals (using electronic cleaner and fine sandpaper), replaced the waterproof seal, cleared the sill drain holes to ensure proper drainage, and resolved the fault.
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.