AU
B16C5

DTC B16C5 indicates an internal fault or critical function failure in the airbag control unit (SRS ECU) — Seal 6 EV

Safety System

DTC B16C5 indicates an internal fault or critical function failure in the airbag control unit (SRS ECU).

The SRS ECU is the core controller of the safety system.

It monitors vehicle collision acceleration, processes crash signals, and controls the ignition triggering of protective devices such as airbags and seat belt pretensioners.

The following conditions trigger this DTC: ECU internal main control chip (MCU) self-test failure, abnormal internal acceleration sensor signal, ignition circuit driver fault, EEPROM read/write error, or persistent ECU power supply voltage or communication bus abnormalities.

When this fault occurs, the SRS system may enter fail-safe mode, preventing normal airbag deployment during a collision or, in extreme cases, causing unintended deployment.

This critical fault directly compromises occupant safety.

The B16C5 fault code on the Seal 6 EV indicates an internal fault or critical function failure in the airbag control unit. Severity is medium because it may affect airbag or seat belt pretensioner operation. Common causes include internal SRS ECU hardware failure or unstable power/ground supply to the ECU. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
4
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1SRS ECU internal hardware damage: Functional failure of the main control chip, internal crash sensor, or ignition drive circuit due to aging, overheating, or electromagnetic interference. Common in 2018-2020 Yuan/Song models.
  • 2Power supply system fault: Excessive contact resistance in the constant power (B+) circuit, unstable IGN supply voltage (below 9V or above 16V), or a poor ground circuit causing an abnormal ECU reset. This typically occurs when the battery is low or after installing an aftermarket audio system.
  • 3CAN bus communication fault: SRS ECU and vehicle network communication interrupted or message timeout. Possible causes include wiring harness short circuit, connector water ingress (e.g., poor sealing at the wiring harness hole below the A-pillar), or abnormal terminating resistance.
  • 4Collision data locked: The vehicle experienced a collision, the ECU internally recorded the collision event and was not reset correctly, or a used ECU was installed without data synchronization.
  • 5Software/calibration error: Corrupted ECU internal Flash data, calibration parameters mismatching vehicle configuration, or interrupted programming causing program integrity check failure.
What To Do
  • 1
    Use VDS2000 or the latest BYD diagnostic tool to read all DTCs, check for accompanying fault codes (such as U-class communication faults or B16XX series sensor faults), and record freeze frame data (vehicle speed, voltage, and temperature at the time of the fault).
  • 2
    Perform a key cycle test: disconnect the battery negative terminal for 5 minutes, reconnect it, and check if the fault code changes to a history code. If it remains a current code, check the SRS ECU power supply: measure connector pin 1 (B+) for 12V constant power, pin 2 (IGN) for 12V with the ignition switch ON, and pin 3 (GND) for less than 1Ω resistance to ground.
  • 3
    Check CAN communication: Measure pins 6 (CAN-H) and 14 (CAN-L) at the diagnostic port. During sleep mode, voltage is approximately 0V. After wake-up, CAN-H measures 2.5-3.5V and CAN-L measures 2.5-1.5V. Verify the waveform is a symmetrical square wave. If voltage is abnormal, inspect the SRS wiring harness section by section (located under the center console and prone to corrosion from A/C condensate leaks).
  • 4
    Visually inspect the ECU exterior: Remove the lower center console trim panel and check the SRS ECU housing for cracks, signs of water ingress (white corrosion), or impact deformation. If signs of water ingress are present, replace the ECU and repair the leak point (commonly a detached sunroof drain hose).
  • 5
    Software repair attempt: If the wiring is normal, use the diagnostic tool to perform 'SRS system calibration' or 'configuration code writing' (enter the vehicle VIN and configuration code). Flashing the SRM (Supplemental Restraint System Module) software version resolves some B16C5-00 faults (confirm the part number supports software upgrades).
  • 6
    Replace the SRS ECU: If the above steps fail, order a new ECU (verify high-spec/low-spec and with/without side airbag configurations). After installation, perform 'crash sensor calibration' and 'system self-learning', and clear all stored fault codes. Dispose of the old ECU as hazardous waste.
Real-World Cases
BYD DTC AI Analysis

B16C5-00 cannot be cleared after collision on Tang DM

✓
2021 Tang DM. After a minor front-end collision and front bumper replacement, the instrument cluster kept displaying the airbag warning light. Scan tool retrieved active DTC B16C5-00, accompanied by B1650-00 (driver airbag module). Inspection found no external damage to the SRS ECU, but it had internally logged the collision and locked. Online reset attempt failed. Replaced the SRS ECU (part number SC-3636900-B1), programmed the vehicle configuration, then completed ‘Restraint System Configuration’ and ‘Longitudinal Acceleration Sensor Calibration’. Fault resolved.
BYD DTC AI Analysis

Wading through water caused ECU internal short circuit in BYD Yuan EV

✓
2019 Yuan EV535. After heavy rain, drove through standing water. The next day the airbag warning light came on. DTC B16C5-00 stored. Removed and inspected the SRS ECU under the floor — the housing seal had aged, letting water in, and the circuit board had green copper corrosion. Measured a B+ short to ground. Replaced the ECU, cleaned up water on the wiring harness, and unclogged the sunroof drains (blockage let water into the A-pillar). Fault fully resolved.
BYD DTC AI Analysis

BYD Song Max intermittent B16C5 with CAN communication fault

✓
2019 Song MAX. Airbag warning light intermittently illuminated when driving on rough roads. Scan tool showed intermittent B16C5 and U0155-00 (lost communication with SRS). Inspection found pin 10 (CAN-H) of the 32-pin SRS ECU connector beneath the centre console had backed out, causing poor contact. Repaired the pin and applied conductive grease. Secured the wiring harness to prevent strain. Fault has not recurred.
BYD DTC AI Analysis

Aftermarket modifications caused abnormal power supply voltage in Qin Pro

✓
2020 Qin Pro petrol. Owner fitted a dashcam by tapping power from the airbag fuse, causing SRS ECU supply voltage fluctuations (minimum measured 8.2 V). Diagnosed DTC B16C5-00 and multiple voltage-related history codes. Restored the factory fuse circuit and ran a dedicated power feed for the aftermarket device. Cleared fault codes; system operation returned to normal. Warning: Never tap power from SRS system fuses (typically SB03, SB07).
Other Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.