AU
B16C7

DTC B16C7 indicates the airbag control unit (SRS ECU/ACU) detected an internal system fault — Seal U

Safety System

DTC B16C7 indicates the airbag control unit (SRS ECU/ACU) detected an internal system fault.

This typically points to an abnormality in the ECU internal microprocessor, non-volatile memory (NVM), power supply monitoring circuit, or safety relay drive circuit.

As a hard or persistent fault, it can force the airbag system into fail-safe mode and disable airbag deployment.

On BYD e-platform and DM models, a gateway communication interruption may accompany this fault, affecting the normal drive logic of the instrument cluster airbag warning lamp.

This Safety Level 2 fault requires immediate repair.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal hardware damage (MCU processor fault, EEPROM data corruption, or power management IC failure)
  • 2Power supply system fault (battery voltage fluctuation, poor contact in ECU power circuit, or poor grounding causing excessive voltage drop)
  • 3CAN bus communication fault (communication loss caused by CAN-H to CAN-L short circuit, short to power or ground, or abnormal terminating resistance)
  • 4External sensor or actuator short circuit (crash sensor internal short circuit or seat belt pretensioner harness short circuit causing ECU protective lockout)
  • 5Corrupted software or calibration data (interrupted flashing, water ingress causing memory data loss, version mismatch)
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal, wait at least 3 minutes to fully discharge the SRS capacitor, and wear an anti-static wrist strap.
  • 2
    Fault confirmation: Connect the diagnostic tool to read all DTCs, record freeze frame data, and check for other SRS fault codes accompanying B16C7 (such as the B16C0-B16C8 series).
  • 3
    Power supply and ground check: Measure the voltage at SRS ECU connector terminals B16 (constant power), B17 (ignition power), and B18 (ground). Standard voltage: 12V ± 0.5V. Verify ground wire resistance is less than 1Ω.
  • 4
    CAN bus check: Measure diagnostic port terminals 6 (CAN-H) and 14 (CAN-L). Normal voltage is approximately 2.5 V (operating state: CAN-H approx. 2.5-3.5 V, CAN-L approx. 1.5-2.5 V). Terminating resistance is approximately 60 Ω.
  • 5
    Wiring harness and connector inspection: Check the SRS ECU connector (usually located in the lower center console) for oxidation or water ingress, check the wiring harness for damage or pinching, and measure the insulation resistance of each sensor harness to ground and power.
  • 6
    Replacement verification: If the wiring is normal, replace the SRS ECU with the same model (verify part numbers match) and perform online matching.
  • 7
    System matching and calibration: Use VDS to execute the 'Airbag ECU Replacement' procedure, write the VIN, perform sensor calibration and system self-check, clear fault codes, and road test to verify.
Real-World Cases
BYD DTC AI Analysis

Tang DM airbag warning light illuminated while driving with fault code B16C7.

✓
2021 Tang DM. Airbag warning light illuminated intermittently while driving. Scan tool showed DTC B16C7. Inspection found loose battery terminals causing voltage to drop below 9V during starting, triggering the SRS ECU low-voltage protection. Tightened the terminals and replaced the aged battery. Cleared the fault codes. Fault resolved.
BYD DTC AI Analysis

Song MAX SRS system inoperative after water ingress

✓
2019 BYD Song MAX. After driving through water, the airbag warning light stayed on with DTCs B16C7 and U0155 (lost communication with SRS). Found water entry in the cabin floor wiring harness connector, causing degraded insulation between CAN-H and CAN-L. Cleaned and dried the harness, replaced the SRS ECU (damaged by voltage surge), re-matched the system, and restored normal operation.
BYD DTC AI Analysis

Yuan EV reports DTC B16C7 after dashboard replacement.

✓
2019 BYD Yuan EV. After accident repairs replaced the instrument panel assembly, the airbag light stayed on. Diagnosis found the battery remained connected during the work, and plugging/unplugging the SRS ECU connector caused a surge current that damaged the ECU's internal power management module. Replaced the SRS ECU with a new one and performed online configuration to resolve the problem.
BYD DTC AI Analysis

Interrupted software flash caused B16C7 on Qin Pro DM

✓
The Qin Pro DM lost power unexpectedly during an SRS system update at the dealership. After restarting, it set code B16C7 which could not be cleared. Inspection found corrupted ECU internal calibration data. Using a dedicated diagnostic scanner, the technician reflashed the latest SRS software and performed the full calibration procedure (including impact sensor zero-point calibration), fixing the fault.
BYD DTC AI Analysis

Sensor short circuit triggered ECU protection on Song Plus DM-i

✓
2022 Song Plus DM-i. Left front impact sensor harness inside the fender damaged, shorting to ground and causing the SRS ECU to enter protection mode, logging DTC B16C7. Repaired the harness insulation, replaced the damaged impact sensor. Cleared fault codes — system self-test passed, airbag warning light off.
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.