AU
B169D00

DTC B169D00 indicates the airbag control unit (SRS ECU/ACU) detects an internal systemic fault — Seal U

Safety System

DTC B169D00 indicates the airbag control unit (SRS ECU/ACU) detects an internal systemic fault.

The ECU sets this code when it detects an abnormality in the processor core, non-volatile memory (NVM), safety sensor interface, or internal communication bus during the Power-on Self Test or cyclic monitoring.

As the core controller of the passive safety system, the SRS ECU monitors crash acceleration sensor signals in real time, processes crash algorithm decisions, and controls the firing circuits for the airbag modules and seat belt pretensioners.

This fault causes the ECU to enter Limp Home mode or fail completely.

Consequently, the ECU cannot correctly determine crash severity or trigger the corresponding protective devices during a collision, leading to airbags failing to deploy or deploying unintentionally.

This is an ASIL-D safety-critical fault.

Potential causes include ECU hardware damage, software runaway, abnormal supply voltage (below 9V or above 16V lasting beyond the set threshold), CAN/LIN communication physical layer faults, or system lockout resulting from a short or open circuit in the external crash sensor wiring.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal hardware fault: damaged main control chip (e.g., Infineon TC2xx/TC3xx series MCU), memory (Flash/EEPROM) data checksum failure, internal safety watchdog timeout
  • 2Power supply and ground system fault: Unstable battery voltage (discharged battery or charging system fault); loose or oxidized dedicated SRS ECU ground points (G101/G102, etc.) causing excessive voltage drop; excessive contact resistance at the constant power (+B) circuit fuse.
  • 3Communication bus fault: Diagnostic CAN or private security CAN bus (CAN-H/CAN-L) short to power/ground, open circuit (common at the instrument panel wiring harness connector), or terminating resistor drift (not the standard 60Ω value) impairing signal integrity.
  • 4Peripheral sensor circuit fault: Front impact sensor (FIS) or side impact sensor (SIS) wiring harness short to ground or short to power, triggering the ECU protective lockout mechanism; water ingress at the sensor connector reducing insulation resistance.
  • 5Software and calibration faults: ECU firmware version defects, corrupted crash threshold calibration data, online configuration (coding) data mismatch with vehicle VIN or hardware version, or interrupted previous flashing process causing data integrity check failure.
What To Do
  • 1
    Use the BYD VDS2000 or DMS diagnostic tool to perform a full system scan. Record the B169D00 freeze frame data, noting the vehicle status when the fault occurred (ignition cycle, vehicle speed, supply voltage). Check for accompanying U-series communication fault codes (such as U0151 Lost Communication With SRS) or B13xx-series sensor fault codes.
  • 2
    Update the SRS ECU software: flash the latest ECU firmware via OTA or offline flashing (typically located in the safety system flashing menu). If the flashing process interrupts or fails, directly diagnose an ECU hardware fault. After a successful flash, perform an ignition cycle test and check if the DTC returns.
  • 3
    Power supply and ground verification: Disconnect the battery negative terminal for 3 minutes. Measure the voltage between SRS ECU connector terminal 30 (constant +B) and ground (should be ≥12.4V). Measure the ground point resistance (should be <0.1Ω). Check the tightness of the ground points in the engine compartment and under the instrument panel. If necessary, sand the mating surfaces and apply conductive grease.
  • 4
    Communication line inspection: Use an oscilloscope to measure the diagnostic CAN line (OBD Pins 6/14) waveform and check for abnormal spikes or level offsets. Turn off the ignition and disconnect the ECU connector. Measure the resistance between CAN-H and CAN-L. The standard value is 60 Ω ± 5 Ω. Inspect the wiring harness for crushing, wear, or water ingress, focusing on the harness junction behind the dashboard frame.
  • 5
    Sensor circuit check: If the above checks are normal, use the special tool to measure the continuity and insulation resistance of the crash sensor wiring. Check the wiring harness connectors at the front bulkhead, A-pillar, and B-pillar for backed-out terminals, oxidation, or poor sealing, especially on accident-repaired vehicles.
  • 6
    ECU replacement and configuration: If the fault persists, replace the SRS ECU assembly. After installing the new ECU, perform online configuration (write the vehicle VIN, model code, and airbag configuration parameters) and read the system configuration to confirm no discrepancies. Finally, perform an airbag system function test (use a dedicated resistor substitute; never directly measure the airbag inflator resistance).
Real-World Cases
BYD DTC AI Analysis

Qin EV: SRS warning light comes on intermittently while driving (communication interference type)

✓
A 2019 Qin EV developed intermittent SRS warning light illumination on the instrument cluster when driving over rough surfaces, which cleared following an ignition cycle. VDS scanning identified DTC B169D00 and intermittent U0151 (lost communication with SRS). Diagnosis revealed a non-genuine dashcam had been installed, with its power feed directly tapped into the SRS ECU supply fuse. This caused the voltage to drop to 8.2V during start-up, triggering the ECU low-voltage protection. Removed the unauthorised wiring, restored the factory fuse configuration, and cleaned the SRS ECU earth point. Fault resolved.
Original source ↗
BYD DTC AI Analysis

SRS ECU wiring harness pin backed out, causing intermittent fault on the E3 EV model.

✓
One week after delivery of a new 2020 BYD E3, the customer reported the SRS warning light constantly illuminated with DTC B169D00 stored. Inspection revealed the constant power pin (Pin 30) for the SRS ECU had backed out at the GJK14 instrument panel harness connector, causing intermittent ECU power. This connector, located behind the driver-side instrument panel reinforcement, was not fully latched during assembly and gradually loosened under vehicle vibration. After re-crimping the terminal and ensuring the connector lock engaged properly, the fault did not recur.
Original source ↗
BYD DTC AI Analysis

Hyundai model B169D00 (LIN communication error) reference case (applicable to BYD diagnostic logic)

✓
Although this case comes from Hyundai technical documentation (DTC B169D00: Right Rear Door Module [RRDM] LIN communication error), its diagnostic logic is highly relevant for troubleshooting LIN/CAN communication faults in BYD SRS systems. Measuring the LIN line resistance to ground revealed an open circuit, traced to a wiring harness fatigue fracture at the door hinge. For BYD SRS systems, similar physical layer faults—such as an open circuit in the LIN sub-bus between the ECU and crash sensors—can trigger B169D00-type communication faults. Focus continuity checks at harness bend points.
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.