AU
B169C00

DTC B169C00 indicates the airbag control unit (SRS ECU) detected a severe fault during its internal self-check — Seal U

Safety System

DTC B169C00 indicates the airbag control unit (SRS ECU) detected a severe fault during its internal self-check.

This typically involves an ECU internal memory (EEPROM/Flash) data checksum failure, a main processor (MCU) calculation error, or an internal power supply/clock circuit fault.

This is a hard fault; the ECU cannot guarantee correct deployment of the airbags, seat belt pretensioners, and high-voltage interlock cut-off function during a collision.

Upon triggering, the SRS ECU enters fail-safe mode, illuminates the instrument cluster airbag warning light, and disables the entire airbag system.

Although the vehicle remains drivable, crash protection functions fail completely, posing a major safety risk.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal memory data corruption or checksum failure (due to electromagnetic interference, voltage transients, or memory aging)
  • 2ECU power supply system fault (unstable constant power (BAT+) or ignition power (IG+) voltage, or ground point oxidation causing reference voltage drift)
  • 3CAN communication bus physical layer fault (CAN-H and CAN-L shorted together or shorted to ground, preventing the ECU from synchronizing with the vehicle network)
  • 4Damaged ECU internal circuit board components (buck converter chip, crystal oscillator, or sensor interface IC failure due to overvoltage or thermal cycling fatigue)
  • 5Software calibration data lost (programming failure or interrupted flash update causing a CRC checksum error in the calibration area)
What To Do
  • 1
    Use the VDS2100/VDS3.0 diagnostic tool to read all DTCs. Confirm B169C00 is a current fault (Active), record the freeze frame data, and check for accompanying U-class communication fault codes.
  • 2
    Perform a key cycle test and observe if the fault code resets. If the fault persists, disconnect the battery negative terminal for 5 minutes, clear the fault code, power on the vehicle, and perform a self-check to verify if the fault returns.
  • 3
    Check the SRS ECU power supply and ground: measure the voltage at connector terminal 1 (BAT+) and terminal 9 (IG+) (should be 9-16V), measure the resistance between terminals 26/27 (GND) and body ground (should be < 1Ω), and check fuses SB03 (10A) and SB10 (10A).
  • 4
    Check CAN bus communication: Measure the resistance between diagnostic connector pin 6 (CAN-H) and pin 14 (CAN-L) (60Ω±2Ω) and the voltage to ground (CAN-H 2.5-3.5V, CAN-L 1.5-2.5V) to rule out wiring short or open circuits.
  • 5
    Check ECU connector (B-211) for water ingress, corrosion, and backed-out pins. Pay special attention to poor contact resulting from loose connector locking tabs, a common issue on early BYD models.
  • 6
    Perform SRS ECU software update: Use the latest diagnostic tool version to perform online programming (ECU Programming) and update the underlying software and calibration data. After updating, perform ECU configuration (Configuration) to write the vehicle VIN and configuration code.
  • 7
    If the above steps fail, replace the SRS ECU assembly (part number varies by model: 10236240-00 for E2, 10236220-00 for Qin EV). After replacement, perform online configuration, calibration, and the collision output test (Output Test).
  • 8
    Final verification: Perform a system self-check and confirm B169C00 no longer appears. Simulate a crash signal test (trigger using the diagnostic tool) and confirm airbag circuit resistance is normal (2.0-3.0Ω). Clear all fault codes. Perform a road test and confirm the instrument warning light turns off.
Real-World Cases
BYD DTC AI Analysis

Following accident repairs, Qin EV SRS light stays on. DTC B169C00: internal fault.

✓
Following accident repairs on a 2019 Qin EV, the airbag warning light on the dash stayed on. VDS read DTC B169C00 (SRS ECU fault) and multiple historical crash codes. Inspection found the SRS ECU had no external damage, but the internal accelerometer had developed zero drift from the impact, so the ECU self-check flagged an internal fault. A software reflash did not clear the fault. Replaced the SRS ECU, reconfigured it, then performed output testing and static calibration. Fault resolved.
BYD DTC AI Analysis

E2 EV SRS system failed after flooding

✓
A 2020 E2’s airbag warning light came on after wading through floodwater. Diagnostics revealed active fault code B169C00. Removing and inspecting the SRS ECU (located beneath the centre console) showed mud traces on the connector and corrosion on the internal circuit board. Cleaning the connector and drying the ECU temporarily cleared the fault, but it returned after two days of driving. Replacing the SRS ECU and applying anti-corrosion treatment to the wiring harness permanently fixed the problem. For flood-damaged vehicles, replace the SRS ECU rather than just cleaning it.
BYD DTC AI Analysis

E3: Software bug causes intermittent airbag warning light while driving.

✓
The airbag warning light on a 2020 E3 came on intermittently while driving and went off after a restart. VDS scan showed stored fault code B169C00. Power, ground and CAN lines checked – no issues. ECU connector tight. A BYD TSB confirmed an early-version software defect that caused the ECU's internal watchdog to reset under certain electromagnetic conditions. Updated SRS ECU software to the latest version (V3.2.1 or higher). No recurrence during one month of monitoring.
BYD DTC AI Analysis

Qin EV triggered B169C00 after aftermarket stereo installation

✓
A 2019 Qin EV showed an SRS warning light the day after having aftermarket audio fitted at a non-authorised workshop. Diagnostics revealed DTCs B169C00 and U0151 (lost communication with SRS). Inspection found the workshop had broken the SRS ECU earth wire (G206) while prying off the centre console, causing an unstable ground for the ECU. Retightened the earth point, cleared the fault codes, and the system returned to normal. Tip: modifications involving SRS wiring easily cause such faults.
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.