AU
B16A1-00

DTC B16A1-00 indicates the Airbag Control Unit (ACU) detected a communication anomaly or internal circuit fault in the Left Side Impact Sensor — Seal U

Safety System

DTC B16A1-00 indicates the Airbag Control Unit (ACU) detected a communication anomaly or internal circuit fault in the Left Side Impact Sensor.

The SRS_ECU continuously monitors the supply voltage, signal circuit resistance, and LIN/CAN communication frame rate of each impact sensor.

The ECU sets this DTC if it detects an open circuit, short to ground, or short to power in the left sensor wiring, or a sensor data validation error (e.g., capacitance drift, acceleration signal out of range) lasting over 200ms.

Once set, the system enters a degraded mode.

This mode may disable the left side airbag and curtain airbag deployment, or on certain models, restrict the entire airbag system, posing a severe safety hazard.

The B16A1-00 fault code on the Seal U indicates the airbag control unit detected a communication or internal circuit fault in the left side impact sensor. This medium severity issue may disable the left side and curtain airbags, posing a safety risk. It is typically caused by a faulty internal accelerometer, degraded capacitor, or damaged wiring connections. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1A damaged internal accelerometer or degraded capacitor in the left side impact sensor (located behind the left B-pillar trim panel) causes abnormal signal output.
  • 2Wiring harness connector between the SRS ECU and the left side impact sensor (typically located under the left front seat or at the base of the B-pillar) is loose, oxidized from water ingress, has backed-out pins, or makes poor contact.
  • 3Airbag Control Unit (ACU) internal memory damage, power supply chip failure, or software logic error causing a false sensor fault report.
  • 4After a left-side collision, loose sensor mounting or internal micro-cracks cause an intermittent open circuit, but the condition does not meet replacement criteria.
  • 5Low 12V battery voltage or excessive voltage drop in the SRS system power supply circuit prevents the ECU from correctly identifying the sensor during initialization.
What To Do
  • 1
    Connect the VDS2000 or dedicated BYD diagnostic tool. Access the SRS system and read all DTCs. Confirm whether B16A1-00 is a current (Active) or historical (History) fault. Record the vehicle speed and sensor voltage values from the freeze frame data.
  • 2
    Disconnect the 12V battery negative terminal. Wait 90 seconds for the capacitors to discharge, then remove the left B-pillar lower trim panel. Check the side impact sensor connector (black plug, 2-pin or 3-pin) for secure locking. Inspect the pins for oxidation or recession. Apply conductive grease if necessary.
  • 3
    Use a multimeter to measure the voltage at the sensor harness connector. With the ignition switch ON, the power pin voltage should be 4.8-5.2V and the signal pin voltage should be 2.3-2.7V. Measure the sensor resistance. The normal range is 1.8-3.2kΩ. Replace the sensor if the deviation exceeds ±10%.
  • 4
    Check wiring harness continuity: Test the wiring harness between the ACU (usually located under the center tunnel) and the left sensor for continuity. Confirm no open circuit exists and insulation resistance is >1MΩ. Inspect the wiring harness near the seat rail for wear.
  • 5
    If the wiring harness and sensor are normal, update the SRS ECU software to the latest version (if available), or perform the 'Sensor Configuration' and 'Crash Record Clear' functions. If necessary, replace and recode the ACU control unit.
  • 6
    Reconnect all components, restore power, clear fault codes, and perform a system self-check (wait for the indicator lamp self-check to complete). Finally, perform a road test (including bumpy roads and turns) to confirm the fault code does not recur and the airbag warning lamp turns off.
Real-World Cases
BYD DTC AI Analysis

Loose left B-pillar sensor connector on Qin EV450 causing intermittent fault

✓
A 2018 Qin EV450 with 32,000 km on the clock occasionally displayed "Check SRS System" on the dashboard; the warning cleared after cycling the ignition. Used VDS to retrieve DTC B16A1-00 (intermittent). Inspected the side impact sensor inside the left B-pillar interior trim and found the connector locking tab had broken, allowing the plug to work loose and causing an intermittent connection when driving over bumps. Replaced the sensor wiring harness connector using a wiring repair kit, re-secured the harness routing, and cleared the fault.
BYD DTC AI Analysis

Qin 100 left impact sensor internal circuit damaged

✓
2017 Qin 100. Airbag warning light stayed on. DTC B16A1-00 (current fault) stored. Sensor power supply measured 5.02V (normal), but sensor signal output voltage was 0.3V (abnormal). Replaced left side impact sensor (part number: K9-5820600). The DTC changed to historical; after clearing it did not reappear. Cause: damaged accelerometer chip inside the sensor.
BYD DTC AI Analysis

Sensors not calibrated after accident repair on Qin EV300

✓
2017 Qin EV300. After a minor left-side collision, an outside shop replaced the left front door and B-pillar outer panel, then the airbag light came on. Diagnostics showed B16A1-00 with B1650-00 (crash data stored). Inspection revealed the shop had reinstalled the left impact sensor but under-torqued the mounting bolts, causing the sensor angle to shift. Re-torqued the bolts to 8 N·m, then used VDS to run impact sensor zero-point calibration and crash data clear. Fault resolved.
BYD DTC AI Analysis

Wiring harness chafing caused a short to earth.

✓
The airbag warning light on a BYD Qin 80 suddenly illuminated while driving. Inspection found the wiring harness protective sleeve near the left front seat rail damaged. The side impact sensor signal wire had chafed against the seat mounting bracket, causing an intermittent short to earth. Repaired the wire by soldering and insulating with heat-shrink tubing, rerouted the harness to avoid the seat slide travel, and replaced the damaged corrugated tubing. Fault resolved.
BYD DTC AI Analysis

SRS ECU software fault causing false alarms

✓
2017 BYD Qin 100. No obvious collision history, but DTC B16A1-00 kept recurring. Replaced the sensor and wiring harness, yet the fault persisted. Checked ACU software version: V1.2. Consulted BYD TSB and found that version has a false-positive defect. Upgraded ACU software to V1.5 and performed sensor configuration matching. The fault has not returned.
Other Seal U Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.