AU
B16AD

DTC B16AD indicates an internal fault or critical communication error in the airbag control unit (SRS ECU) — Seal U

Safety System

DTC B16AD indicates an internal fault or critical communication error in the airbag control unit (SRS ECU).

This fault points to a hardware-level failure in the ECU internal microprocessor, non-volatile memory (EEPROM/Flash), power management module, or acceleration sensor interface circuit, rather than an external wiring issue.

The ECU sets this code when its self-check detects a failed internal diagnostic test, a calibration data checksum error, a watchdog reset, or a critical circuit voltage deviating from threshold limits.

This fault forces the SRS system into fail-safe mode: the system either completely disables the airbags (no deployment during a collision) or enters a degraded mode (only partial circuits operate), and illuminates the airbag warning lamp.

Because this fault affects the passive safety system, the vehicle remains drivable but poses a severe safety risk.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal hardware fault: Damaged ECU main control chip (MCU), memory, or power supply voltage regulator circuit. Common causes include aging from long-term vehicle use, overheating, or voltage surges (such as reversed polarity during jump-starting).
  • 2Power supply system fault: unstable battery voltage (persistently below 9V or above 16V), poor contact at the dedicated SRS fuse, or ECU ground terminal oxidation causing reference voltage drift, triggering internal ECU undervoltage/overvoltage protection.
  • 3CAN bus communication fault: Power CAN or dedicated SRS-CAN bus short circuit (short between CAN-H and CAN-L, short to power, or short to ground), open circuit, or abnormal terminating resistance causes an ECU communication timeout with the vehicle network.
  • 4Software or calibration data corrupted: Electromagnetic interference, interrupted programming, or physical memory damage corrupts ECU internal Flash data, causing a self-test checksum failure.
  • 5Physical damage or water ingress: Front-end collision deforms the ECU housing and cracks the internal PCB, or a blocked drain channel allows water into the ECU mounting compartment (usually located under the center console or central tunnel) and corrodes the circuit board.
What To Do
  • 1
    Initial diagnosis and safety preparation: Connect the BYD VDS2000/Launch X431 diagnostic tool. Read all DTCs and freeze frame data to confirm if B16AD is an active or history code. Disconnect the battery negative terminal and wait 3 minutes for capacitors to discharge. Inspect the SRS ECU for physical damage, water stains, or burn marks.
  • 2
    Power and ground circuit inspection: Reconnect the battery, turn the ignition switch to ON (do not start), and measure the voltage to ground at ECU connector pin 16 (B+ constant power) and pin 15 (IGN power); the voltage should be 12V±0.5V. Measure the resistance to ground at pin 14 (ground); the resistance should be less than 1Ω. Check the connector terminals for backed-out pins or oxidation.
  • 3
    CAN bus communication check: Use an oscilloscope to measure the waveforms at ECU CAN-H (pin 6) and CAN-L (pin 7). Verify square waves with a 2.5 V reference and 3.5 V/1.5 V dominant levels. Measure the termination resistance; the value must be approximately 60 Ω (two 120 Ω resistors in parallel). Check the wiring harness for wear or crushing.
  • 4
    ECU replacement and cross-check: If the wiring is normal, replace the SRS ECU with a known-good unit of the same part number for testing (perform immobilizer matching pre-processing first). If the fault disappears after replacement, confirm an internal fault in the original ECU. If the fault persists, check the wiring harness for an intermittent open or short circuit.
  • 5
    Programming and calibration: After replacing the ECU, use the diagnostic tool to perform 'Airbag System Configuration' (Coding) and 'Sensor Calibration' (Calibration). Write the vehicle VIN and airbag configuration parameters (such as single/dual-stage airbags, number of side curtain airbags, etc.).
  • 6
    System verification and final inspection: Clear all DTCs and perform the 'system self-diagnosis test' (trigger using a dedicated tool or diagnostic tool command). Check the resistance of the seat belt pretensioner and each airbag circuit (normal: 2.0-3.0Ω). After a road test, read the fault codes again. Confirm B16AD does not return and the instrument cluster airbag warning light turns off normally.
Real-World Cases
BYD DTC AI Analysis

BYD Tang DM-i SRS ECU internal processor fault

✓
Vehicle: 2021 Tang DM-i, 32,000 km. Symptoms: Airbag warning light constantly on; DTC B16AD (current). Diagnosis: Measured ECU power supply at 12.4V – normal; CAN bus waveform normal. Disassembled ECU and found obvious overheating marks near the internal main control chip (Renesas R8C series), with localised PCB carbonisation. Analysis determined the internal power regulator module had failed, causing unstable processor power supply. Resolution: Replaced SRS ECU with new unit (part number: SC-3638100), performed online configuration programming, fault resolved.
BYD DTC AI Analysis

CAN communication fault on BYD Yuan EV caused DTC B16AD

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Vehicle: 2019 Yuan EV535. Symptoms: Intermittent airbag warning light, frequent on bumpy roads. Diagnosis: DTC B16AD was intermittent. CAN bus static resistance was normal. Bump testing revealed the CAN-H wiring harness chafed at the dashboard frame, causing an intermittent short to ground (resistance fluctuating between 5-50Ω). The short interrupted ECU communication for over 500ms, triggering ECU fail-safe and logging B16AD. Solution: Repaired the damaged harness (rewrapped and rerouted) and fitted protective sleeving. Fault has not recurred.
BYD DTC AI Analysis

BYD S6: Abnormal battery voltage caused ECU protection

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Vehicle: BYD S6 (petrol), after high-power audio system modification. Symptoms: Airbag light illuminates at startup, logs DTC B16AD. Diagnosis: Voltage captured dropping to 7.2V during cranking, below the ECU operating threshold (8V). The cause: the modified audio system drew power from the SRS fuse holder, causing momentary undervoltage and ECU reset at startup. Repair: Rerouted the audio power feed directly to the battery positive terminal, replaced the fuse with an OEM-spec fuse, and cleared the fault codes. System operated normally after.
BYD DTC AI Analysis

Water immersion caused SRS ECU corrosion in a BYD Song MAX.

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Vehicle: 2019 BYD Song MAX, after driving through water. Symptoms: Airbag warning light on, history of blocked air conditioning drain. Diagnosis: Removed centre console and found water in the SRS ECU mounting bracket. The ECU housing seal had aged, causing water ingress. Internal PCB showed multiple areas of green copper corrosion. DTC B16AD present along with multiple airbag circuit high-resistance fault codes. Fix: Replaced SRS ECU, unblocked air conditioning drain hose, dried wiring harness connectors, replaced ECU mounting bracket seal.
BYD DTC AI Analysis

BYD Qin Pro software calibration lost

✓
Vehicle: 2020 Qin Pro, after accident repairs. Symptoms: Airbag warning light on after front bumper replacement, DTC B16AD stored. Diagnosis: The new SRS ECU was blank, with no vehicle configuration data programmed. Scan tool read ECU internal coding as all FF (uncoded state), causing self-test failure. Solution: Performed SRS ECU online coding using the BYD dedicated diagnostic tool. Selected the configuration (front dual airbags + side curtain airbags), wrote crash sensor sensitivity parameters, and completed calibration. Fault cleared.
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.