AU
B169F00

DTC B169F00 indicates the Airbag Control Unit (SRS ECU) detected a severe fault during its internal self-test — Seal U

Safety System

DTC B169F00 indicates the Airbag Control Unit (SRS ECU) detected a severe fault during its internal self-test.

As the core controller of the passive safety system, the SRS ECU integrates lateral/longitudinal acceleration sensors, the crash algorithm processor, and the ignition drive circuit.

This DTC triggers when the ECU internal processor, memory (EEPROM/Flash), power monitoring module, or internal communication bus experiences an irreversible hardware or software anomaly.

Upon detecting this fault, the ECU enters a degraded mode and may disable the ignition output for the airbags and seat belt pretensioners, resulting in partial or complete loss of crash protection functions.

This safety-critical fault requires immediate action.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal hardware fault: Main control chip (MCU) damage, internal acceleration sensor signal processing circuit fault, igniter drive transistor breakdown, or memory data checksum failure.
  • 2Power supply system fault: battery voltage below 9V or above 16V; poor contact at dedicated SRS fuse (usually 10A or 15A); loose connection in ECU constant power (B+) or ignition power (IG) circuit; corroded ground terminal causing reference voltage drift.
  • 3CAN network communication fault: A short or open circuit in the Power CAN or Comfort CAN bus prevents the ECU from communicating normally with the Vehicle Control Module (VCM) and Instrument Cluster Module (ICM), triggering a watchdog reset.
  • 4Software or calibration data corrupted: missing program segments due to flashing interruption, uncleared latched crash data, or calibration data (coding) mismatch with vehicle configuration.
  • 5Environmental factors: moisture inside the ECU (wading or A/C condensate leakage), thermal fatigue cracking of circuit board solder joints (long-term high-temperature environment), electromagnetic interference causing processor program runaway
What To Do
  • 1
    Perform a deep scan using the BYD VDS2000/3000 diagnostic tool. Record all fault codes and freeze frame data. Check specifically for accompanying B16XX series sensor faults or U-class communication faults.
  • 2
    Perform a power integrity check: measure battery static voltage (should be ≥12.4V); check continuity and insertion force of the SRS fuse in the instrument panel fuse box (F1/16 or F2/08, depending on vehicle model); measure voltage to ground at ECU connector terminals B01-1 (B+) and B01-2 (IG); and check resistance to ground at B01-3 (GND) (should be <1Ω).
  • 3
    Communication line check: Disconnect the ECU connector. Measure the terminal resistance between CAN-H (B01-12) and CAN-L (B01-13) (should be ≈60Ω) and the voltage to ground (CAN-H ≈2.6V, CAN-L ≈2.4V) to rule out a short or open circuit in the wiring.
  • 4
    Perform software update: If the wiring is normal, update the SRS ECU software (SVM code: SRS_xxx). After the update, perform coding and calibration operations, including the seat occupancy sensor (OCS) and seat belt pretensioner configuration.
  • 5
    Component replacement and verification: If the fault persists, replace the SRS ECU (verify the part number based on the vehicle model, e.g., EG-3636100 for E2). Perform online anti-theft matching and write the safety configuration to the new ECU. After replacement, use a dedicated resistor to simulate the crash sensor and perform a static ignition test. Finally, perform an on-vehicle crash calibration verification.
Real-World Cases
BYD DTC AI Analysis

Qin EV SRS ECU CAN communication fault causing intermittent warning

✓
The airbag warning light would intermittently illuminate whilst driving and clear after an ignition cycle. A VDS scan revealed DTC B169F00 and multiple U-class communication fault codes. In-depth inspection found the bolt at SRS ECU earth point G106 (below left A-pillar) had loosened, causing unstable power supply when driving over bumps and triggering the internal voltage monitoring circuit into fail-safe mode. Re-tightened the earth bolt, cleared the fault codes, and monitored for one week with no recurrence.
Original source ↗
BYD DTC AI Analysis

E2 BEV SRS ECU memory data corruption repair

✓
After accident repairs, we replaced the airbag but the SRS warning light stayed on. The diagnostic tool read code B169F00, which returned after clearing. Inspection found the high current surge during the accident damaged the EEPROM data area inside the ECU. We fitted a new SRS ECU (Part No. EG-3636100A) and used VDS for online configuration: write VIN, configure seat type (5-seat/7-seat), match seatbelt pretensioner resistance (2.0Ω±0.1Ω). The system then passed the self-test.
BYD DTC AI Analysis

Model E3 SRS ECU internal short circuit after water exposure

✓
The airbag warning light stayed on after driving through water. Diagnosis showed DTC B169F00. Disassembly revealed the SRS ECU mounted beneath the centre console. A blocked air conditioning drain hose had caused condensate accumulation, and the aged ECU housing seal allowed water ingress. Opening the ECU showed corrosion on the circuit board and oxidised chip pins. Replaced the ECU, repaired the air conditioning drain hose, cleaned the wiring harness connectors, and applied anti-corrosion treatment. Fault resolved.
BYD DTC AI Analysis

The software update interruption corrupted the SRS ECU program.

✓
During an OTA update at the dealership, insufficient vehicle battery voltage (11.2V) aborted the SRS system flash. At the next start-up, the SRS warning light stayed on and the system logged DTC B169F00 that would not clear. An attempt to enter Boot mode for low-level reflash failed, indicating damaged Flash memory blocks. After replacing the SRS ECU, a dedicated regulated power supply (14V/30A) maintained voltage stability during the reflash of the latest software (Ver 3.2.1) and collision sensor calibration. This resolved the fault.
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.