AU
B169C

DTC B169C indicates the airbag control unit (SRS ECU) detects a critical internal function failure or self-diagnostic abnormality — Seal U

Safety System

DTC B169C indicates the airbag control unit (SRS ECU) detects a critical internal function failure or self-diagnostic abnormality.

This typically involves an ECU internal processor (MCU) calculation error, a non-volatile memory (EEPROM/Flash) data verification failure, abnormal power management module (PMIC) output, or the safety monitoring circuit (Watchdog) triggering a reset.

As the core of the passive safety system, the SRS ECU receives crash sensor signals, determines collision severity, and triggers airbag deployment and seat belt pretensioners.

This fault means the ECU cannot guarantee a normal response during a collision, potentially causing the airbags to fail to deploy or deploy unintentionally.

This constitutes an Automotive Safety Integrity Level (ASIL) D functional safety fault.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal hardware fault: damaged main control chip (e.g., Infineon TriCore series), corrupted memory data block, or failed internal voltage regulator (supplying 5V/3.3V sensor reference voltage)
  • 2Power supply system fault: Poor connection in the constant power (B+) circuit, voltage drop in the ignition switch power supply (IG1/IG2), or corrosion at ground points (G101/G102, etc.) causing increased contact resistance (>1Ω).
  • 3Communication bus fault: Short circuit between CAN-H and CAN-L, short to power or ground, or terminating resistor drift (standard 60Ω, deviation exceeding 5Ω), preventing the ECU from conducting security authentication communication with the BCM and instrument cluster.
  • 4Sensor circuit fault: A short circuit in the power supply line of the front impact sensor (G sensor) or side pressure sensor triggers the ECU internal power protection circuit, activating fail-safe mode.
  • 5Software/calibration data corruption: Power loss during vehicle flashing or strong electromagnetic interference (EMI) causing Flash data errors or CRC check failure.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds (to completely discharge the SRS ECU internal energy storage capacitor). Inspect the ECU exterior for physical damage, water ingress, or burn marks.
  • 2
    Power supply and ground check: Use a multimeter to measure the voltage at ECU connector terminal 30 (constant power) and terminal 15 (ignition power). The standard value is 11-14V. Measure the ground resistance; the value must be less than 1Ω. Check the fuse (usually a dedicated 10A-15A fuse in the instrument panel fuse box).
  • 3
    Communication line diagnosis: Use an oscilloscope to check the CAN waveform (dominant level 2.5-3.5V, recessive level 1.5-2.5V), measure the terminating resistance (60Ω±5Ω), and inspect the wiring for wear or short circuits.
  • 4
    Sensor circuit check: Disconnect the rear crash sensor connector, measure the sensor supply voltage on the ECU side (standard 5V±0.25V), and check the insulation of each sensor circuit to ground/power supply (>1MΩ).
  • 5
    Replacement verification: If the wiring is normal but the fault code persists, replace the SRS ECU with a unit of the same part number (Note: Some BYD models bind the ECU to the key immobilizer system or VIN; confirm part compatibility).
  • 6
    Programming and configuration: Use the VDS2000/3000 or ED-400 diagnostic tool to perform: ① ECU Coding; ② Variant Coding (configure airbag stages, seat types, etc.); ③ Safety Configuration Writing (write VIN, match sensor IDs).
  • 7
    System verification: Reconnect the power supply, clear the fault code, and perform the SRS system self-check (the indicator light should illuminate for 6 seconds and then turn off). Use the diagnostic tool to read the live data stream and confirm each sensor status is 'normal'. Perform an offline crash simulation test (special equipment required) to verify the deployment circuit resistance (2.0-3.0Ω).
Real-World Cases
BYD DTC AI Analysis

Loose power connection caused intermittent SRS ECU fault in Tang DM

✓
Symptoms: Instrument panel airbag warning light illuminated intermittently. Retrieved fault codes B169C (current) and B169C-00 (history). Diagnosis: Measured ECU supply voltage and found Terminal 30 fluctuating between 12.1V and 11.4V (should remain stable above 12.6V). Traced the fault to internal oxidation in the main wiring harness between the battery positive terminal and fuse box. Contact resistance measured 3.2Ω. Resolution: Replaced the battery positive cable assembly, cleaned and tightened all earth points. Fault resolved.
BYD DTC AI Analysis

Yuan EV CAN bus short circuit causes SRS communication fault

✓
Symptoms: Vehicle fails to engage high voltage; dashboard displays 'Please check SRS system'. DTCs B169C and U0151 present (loss of communication with SRS). Diagnosis: Measured OBD port CAN line resistance at 0Ω (short between CAN-H and CAN-L). Sectional inspection found the right A-pillar wiring harness had been crushed during carpet removal/installation, damaging the insulation and causing a short in the twisted pair. Resolution: Repaired the harness insulation, rerouted the harness to avoid the pedal mechanism, and confirmed normal CAN waveforms (rectangular waves without distortion).
BYD DTC AI Analysis

Collision sensor power supply fault triggered ECU protection — Song MAX

✓
Symptoms: After accident repair, the airbag warning light stays illuminated with fault codes B169C and B1620 (left front impact sensor fault). Diagnosis: Inspection found the left front impact sensor wiring harness damaged during the accident. The 5V supply wire shorted to ground, triggering the SRS ECU internal voltage regulator overload protection. Solution: Replaced the left front impact sensor and wiring harness. Performed 'Sensor ID Learning' and 'Configuration Reset' using a diagnostic tool. Cleared fault codes; system returned to normal.
BYD DTC AI Analysis

Software calibration error caused ECU self-test failure in Qin Pro

✓
Symptoms: After replacing the instrument panel assembly, the airbag warning light stays on with DTC B169C (configuration error). Diagnosis: The new instrument cluster communicates normally with the SRS ECU, but reading the ECU variable configuration found that 'seat occupancy recognition' was incorrectly coded as 'equipped' when the vehicle lacks this feature, causing the ECU safety algorithm self-check to fail. Solution: Used the VDS diagnostic scanner to modify the variant coding, changing the seat type to 'standard seat'. Performed an ECU reset and the fault code cleared.
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.