AU
B169F-00

DTC B169F-00 indicates the Airbag Control Unit (SRS ECU) detected a severe internal self-check fault, preventing normal system operation — Seal U

Safety System

DTC B169F-00 indicates the Airbag Control Unit (SRS ECU) detected a severe internal self-check fault, preventing normal system operation.

As the core of the passive safety system, the SRS ECU monitors subsystems in real time, including crash acceleration sensors, side pressure sensors, and seat occupancy detection.

Upon detecting a collision, the ECU triggers the airbags, seat belt pretensioners, and high-voltage interlock cut-off.

This fault indicates a hardware-level error in the internal ECU processor, memory unit, power management module, or communication interface, or a communication interruption or error between the ECU and the vehicle network (CAN/LIN).

When this fault triggers, the SRS system enters fail-safe mode and the airbag warning lamp illuminates continuously.

All airbags and pretensioners disarm and may fail to deploy during an actual collision.

Additionally, the vehicle high-voltage system may fail to execute the collision power cut-off, creating a severe safety hazard.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal circuit board fault: Long-term thermal cycling causes capacitor swelling, cold solder joints, or internal processor chip damage.
  • 2Power supply system fault: Low battery charge or alternator regulator fault causes voltage to drop below 9V or rise above 16V, exceeding the ECU operating range.
  • 3Poor connector contact: Oxidized or backed-out ECU pins, loose locking tabs, or wiring harness wear causing intermittent open/short circuits.
  • 4Communication circuit fault: A short circuit, open circuit, or abnormal resistance in the CAN-H/CAN-L circuit interrupts communication between the ECU and the vehicle network.
  • 5Software/calibration data corrupted: flash failure, electromagnetic interference, or electrostatic discharge causing ECU internal data checksum failure.
What To Do
  • 1
    Safety preparation: Set the power mode to OFF, disconnect the battery negative terminal, and wait at least 90 seconds to fully discharge the SRS system capacitor.
  • 2
    Visual inspection: Remove the instrument panel trim. Inspect the SRS ECU for physical damage or signs of water ingress. Verify the connector is secure and the locking tab is engaged.
  • 3
    Power supply and ground check: Use a multimeter to measure the voltage at the ECU power supply pin (standard: 9-16 V) and check the ground wiring harness resistance (must be less than 1 Ω).
  • 4
    Communication line inspection: Measure CAN bus voltage (CAN-H approximately 2.6-2.8 V, CAN-L approximately 2.2-2.4 V) and terminal resistance (approximately 60 Ω).
  • 5
    Connector handling: If pins show oxidation, clean them with a dedicated electronic contact cleaner. Adjust pin tension if necessary to ensure reliable contact.
  • 6
    Component replacement test: If the above checks are normal but the fault code fails to clear, replace the SRS ECU with a known-good unit for verification.
  • 7
    System reset and verification: After installing the new ECU or repairing the wiring, reconnect the battery and switch the ignition to ON. Use the diagnostic tool to clear the fault code and perform a system self-check. Confirm the SRS warning light turns off normally.
  • 8
    Road test verification: Perform a vehicle road test, including bumpy road sections, to confirm the fault does not recur.
Real-World Cases
BYD DTC AI Analysis

Internal circuit fault in SRS ECU

✓
Symptoms: Airbag warning light stayed on continuously. DTC B169F-00 logged; no collision history. Diagnosis: Disconnected battery for 90 seconds, then removed dashboard trim panel. Inspected ECU and connectors visually – both appeared normal. Supply voltage measured within 9–16 V (normal). Fault code could not be cleared, or cleared briefly and then returned. Determined internal ECU circuit failure. Repair: Replaced SRS ECU with new unit. Secured three bolts with a Torx key, connected wiring connectors, refitted trim panel, then reconnected battery. Powered on, cleared fault code, waited 20 seconds. System self-check passed.
Original source ↗
BYD DTC AI Analysis

Poor contact at SRS ECU connector

✓
Symptoms: SRS warning light illuminates intermittently while driving, more prevalent on rough surfaces. The light sometimes extinguishes automatically after stopping and restarting the vehicle. Fault codes appear intermittently. Diagnosis: Inspected the ECU connector on the crossmember. The connector latch was not fully engaged. Pins showed minor oxidation and burn marks. After cleaning and resecuring the connector, the fault still recurred. The cause was an intermittent communication failure due to excessive contact resistance. Resolution: Thoroughly cleaned the pins using dedicated electronic connector cleaner. Adjusted spring clip tension to ensure firm contact. Reconnected the harness and ensured the latch engaged fully (audible click). Secured the wiring harness with cable ties to prevent vibration-induced movement. Road tested for 20 km; the fault did not recur.
Original source ↗
BYD DTC AI Analysis

SRS ECU supply voltage abnormal

✓
Symptoms: SRS system inoperative after vehicle start-up; SRS warning lamp illuminated continuously; possible other electronic system faults; intermittent communication between diagnostic tool and ECU. Diagnosis: Inspected SRS fuse in instrument panel distribution box – intact. Disconnected ECU connector and measured supply pin voltage; found voltage abnormal (below 9 V or above 16 V). Further inspection revealed an aged battery with excessive internal resistance, or loose connections and corrosion in the power supply wiring. Resolution: Replaced the battery with a new one, or repaired the charging system fault. Repaired loose connections in the power supply wiring and cleaned corroded earth points. Replaced the entire power wiring harness where necessary. Ensured system voltage stabilised at 12–14 V. Cleared fault codes and verified normal operation by restarting the vehicle multiple times.
Original source ↗
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.