AU
B16A1

DTC B16A1 indicates the airbag control unit (SRS ECU) detects an internal fault or abnormal communication with connected left-side safety system components — Seal U

Safety System

DTC B16A1 indicates the airbag control unit (SRS ECU) detects an internal fault or abnormal communication with connected left-side safety system components.

Specific causes include an SRS ECU internal processor error, memory fault, software anomaly, or a communication interruption with the left side impact sensor (left B-pillar), left seat belt pretensioner, or left seat occupancy detection sensor.

This critical airbag system fault indicates the ECU may fail to receive left-side impact signals or execute airbag deployment commands.

Consequently, the left side airbag, side curtain airbag, or seat belt pretensioner may fail to deploy during a side impact.

This severely degrades vehicle passive safety protection and requires immediate repair.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal circuit board fault, processor crash, or incorrect software version.
  • 2Left side impact sensor (located in the left B-pillar or left front door) damaged, connector loose, or wiring open/short circuit.
  • 3Abnormal left seat belt pretensioner circuit resistance (open circuit, short circuit, or resistance outside the standard 2.0-3.0 Ω range)
  • 4Abnormal SRS ECU power supply voltage (low battery, blown fuse, poor ground connection)
  • 5Water ingress, corrosion, or oxidation in the left safety system wiring harness connector, or CAN/LIN bus interference.
What To Do
  • 1
    Use the VDS2000/VDS3000 diagnostic tool to read all fault codes and freeze frame data. Confirm B16A1 is a current fault and check for accompanying left-side safety component fault codes (such as B16A0, B16A2).
  • 2
    Check the SRS ECU power supply circuits (including constant power +B and ignition power) and ground circuits. Measure the voltage to verify it remains stable between 11-14V. Check if fuses SB02, SB03, etc., are blown.
  • 3
    Check the connection status of the left side impact sensor connector (located behind the left B-pillar trim panel or in the left front door). Measure the sensor resistance (typically 2.0-3.0 kΩ; refer to the vehicle repair manual for specific values).
  • 4
    Check the continuity and insulation of the left seat belt pretensioner and seat occupancy sensor wiring, verify the circuit resistance is within the standard range, and check the connector for oxidation.
  • 5
    Check the SRS system CAN bus communication (CAN-H and CAN-L) voltage (normally around 2.5V) and waveform to confirm no short to ground or external power supply.
  • 6
    If the wiring inspection is normal, attempt to flash/upgrade the SRS ECU software. If the fault persists, replace the SRS ECU control unit and perform online coding configuration, safety system calibration, and the crash sensor self-test procedure.
Real-World Cases
BYD DTC AI Analysis

BYD Han EV B16A1 Fault (Left B-Pillar Sensor Communication Error)

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Symptoms: Dashboard intermittently displayed safety system warning light. Diagnostic tool read DTC B16A1 (left B-pillar area sensor communication fault). Diagnosis: Inspected the left B-pillar lower wiring harness and found the retaining clip was loose. The harness had chafed against the body metal edge, damaging the CAN-H wire insulation and causing a short to ground. Signal voltage was only 1.2V. Fix: Repaired the damaged CAN-H wire and insulated it with heat shrink tubing. Re-secured the harness routing and added anti-chafe sleeving. Cleared the fault codes and performed the sensor calibration procedure. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Song Plus DM-i B16A1 Fault (Left Door Safety System LIN Communication)

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Symptoms: Intermittent failure of driver's side window operation, delayed response from door lock actuators, and intermittent failure of left front door control functions. Diagnosis: Connected a diagnostic scan tool and confirmed DTC B16A1 is related to communication timeout with the left front door control module (DCM). Measured the wiring harness connector below the left A-pillar and found abnormal LIN bus voltage (pulled down to 0.8V). Disassembly revealed the wiring harness at the door hinge had suffered long-term flexing damage, causing the insulation on both the LIN wire and ground wire to break and short together. Repair: Separated the shorted LIN and ground wires and insulated each individually. Added protective corrugated tubing to the wiring harness at the door hinge. Replaced the left front door control module and recalibrated the window anti-pinch function.
Original source ↗
BYD DTC AI Analysis

BYD Tang DM B16A1 fault (left seat belt pretensioner communication fault)

✓
Symptoms: SRS warning light stayed on after accident repairs. Diagnosis: Scanned SRS system; DTC B16A1 indicated left seat belt retractor sensor. Checked the seat belt assembly inside the left B-pillar trim and found the aftermarket unit installed during the accident repair had an incorrect connector type. Measured sensor resistance—it deviated significantly from standard values (2.4–3.6 Ω). Compared left and right data streams; the left side showed no signal feedback. Repair: Replaced the aftermarket seat belt assembly with a genuine left side unit (with pretensioner and sensor). Reprogrammed and calibrated the airbag system. Cleared fault codes, ran impact sensor self-test; the warning light went out.
Original source ↗
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.