AU
B169B-00

DTC B169B-00 indicates an internal self-diagnostic fault or severe communication error within the airbag control unit (SRS ECU) — Seal U

Safety System

DTC B169B-00 indicates an internal self-diagnostic fault or severe communication error within the airbag control unit (SRS ECU).

This fault indicates the microprocessor, memory (EEPROM/Flash), power supply monitoring circuit, or watchdog circuit within the SRS ECU detected an abnormality, preventing guaranteed airbag deployment.

When this fault occurs, the SRS ECU enters fail-safe mode, illuminates the airbag warning light, and disables all airbags, seat belt pretensioners, and crash unlock functions, severely compromising passive safety.

This is a Hard Fault; disconnecting the power typically will not clear it.

Repair the power supply or communication wiring, or replace the ECU.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1SRS ECU internal circuit board damage: Voltage surges (such as reversed polarity during jump-starting or charger surges), long-term thermal cycling causing solder joint cracking, or internal capacitor aging causing power supply filtering failure.
  • 2Abnormal power supply: Prolonged low (<9V) or high (>16V) battery voltage, loose connection in the IGN power circuit, poor fuse contact, or oxidation at ground point G201 (left side of instrument panel) causing reference voltage drift.
  • 3CAN bus communication fault: Short or open circuit in the CAN-H (orange/black) or CAN-L (orange/brown) wiring between the SRS ECU, gateway, and vehicle control unit; abnormal terminal resistance (120Ω); or bus voltage outside standard values (CAN-H 2.5-3.5V, CAN-L 1.5-2.5V).
  • 4Software or calibration data corrupted: Interrupted flashing process, calibration data checksum failure, or physical damage to the Flash memory prevents the ECU from loading the correct airbag deployment algorithm and crash threshold parameters.
  • 5External environmental factors: Water ingress into the SRS ECU due to vehicle wading (prone to moisture due to its installation position below the air-conditioning evaporator box), minor collision damage not immediately apparent, or strong electromagnetic interference (such as high-power radio equipment) causing an abnormal CPU reset.
What To Do
  • 1
    Diagnostic scan: Use VDS2000 or a dedicated BYD diagnostic tool to access the SRS system and read Freeze Frame data. Confirm whether B169B-00 is an Active or History fault. Record parameters at the time of the fault, including vehicle speed, battery voltage, and temperature. Check for accompanying fault codes (such as U-prefix communication faults or B16XX-series sensor faults).
  • 2
    Power supply and ground check: Turn off the ignition switch. Measure the voltage to ground at pin 16 (constant B+) and pin 15 (IGN) of the SRS ECU connector; the voltage must be within 11-14V. Measure the resistance between the ground pin (usually pin 14) and the vehicle body; the resistance must be <1Ω. Check if fuses SB11 (10A, instrument panel power distribution box) and SB15 (15A) are blown or have poor contact. Check the power supply waveform using an oscilloscope to rule out excessive ripple voltage (>100mV).
  • 3
    CAN bus inspection: Disconnect the SRS ECU connector. Measure the resistance between CAN-H and CAN-L (approximately 60Ω, two 120Ω terminating resistors in parallel). Check for short circuits between CAN-H and ground, CAN-L and ground, and CAN-H and CAN-L. Capture the waveform using a CAN analyzer. Verify the dominant level (CAN-H 3.5V / CAN-L 1.5V) and recessive level (2.5V) are normal. Check for abnormal bit stuffing errors.
  • 4
    ECU inspection: Remove the SRS ECU located beneath the centre console or behind the glovebox (exact location varies by model; on Qin series models, it is typically on the right side of the A/C evaporator). Check the exterior for water marks, burn damage, cracks, or impact deformation. Measure the output of the ECU internal voltage regulator chip (this typically supplies a 5V reference voltage to the sensors). An abnormal reading confirms internal ECU damage. Note: Never dismantle the ECU casing (due to safety sealing and explosion-proof requirements).
  • 5
    Replacement and Matching: If diagnosing a damaged ECU, replace it with a new SRS ECU with the same part number (e.g., HA2E-5810000A or as per the specific vehicle model). Before installation, disconnect the negative battery terminal for at least 5 minutes. After installation, connect the diagnostic tool to perform 'Online Matching' and 'Coding'. Enter the vehicle VIN and airbag configuration parameters (such as the presence of side or knee airbags). Execute 'System Self-check' to clear the fault code and perform a simulated ignition test. Use the diagnostic tool to execute the 'Collision Output Test' function. This operation triggers the airbag warning lamp to flash but does not actually deploy the airbags.
  • 6
    Road test verification: Reassemble the vehicle, start the engine, and confirm the airbag warning lamp turns off after 6 seconds. Perform a road test over bumpy roads and through turns to confirm the fault code does not return. Use the diagnostic tool to read the live data stream. Verify sensor voltages, crash signal status, and CAN communication status are normal. Finally, inform the customer the SRS system is operating normally and emphasize the airbag system was inactive during the repair.
Real-World Cases
BYD DTC AI Analysis

Qin EV450 SRS fault light on after charging

✓
A 2018 BYD Qin EV450 displayed 'Check SRS System' on the instrument cluster after the owner used a non-genuine DC fast charger. Technicians retrieved DTC B169B-00. They found oxidation on the SRS ECU connector. Power supply voltage measurement during fast charging showed a momentary spike to 16.8 V, triggering the ECU's internal overvoltage protection. They replaced the SRS ECU, installed a zener diode protection circuit, and updated the BMS software to limit charging voltage fluctuations. Fault resolved.
BYD DTC AI Analysis

Qin 100 airbag warning light stays on after water ingress.

✓
2017 BYD Qin 100. The vehicle waded through water about 40 cm deep, after which the airbag warning light stayed on. The diagnostic scanner retrieved DTCs B169B-00 and B1650-00 (left impact sensor fault). Disassembly revealed water had entered the SRS ECU mounting location (below the evaporator case) and green corrosion on the circuit board. Replaced the ECU and wiring harness connector, then resealed the area by installing a waterproof cover and applying sealant. Fault resolved. Recommend checking the air conditioning drain hose for blockages.
BYD DTC AI Analysis

ECU communication failure after accident repair

✓
After a front collision repair on a Qin EV300, DTC B169B-00 appeared and could not be cleared. Inspection found the accident deformed the front bulkhead and displaced the SRS ECU mounting bracket, cracking the ECU housing slightly and putting the internal gyroscope sensor out of calibration. The accident also crushed the CAN wiring harness, damaging the insulation and causing an intermittent short circuit. Replaced the SRS ECU, repaired the wiring harness, corrected the installation position, performed online matching, and the fault cleared.
BYD DTC AI Analysis

Software flash failure locked the ECU

✓
During an SRS software upgrade on a Qin 80 at the dealership, the diagnostic tool disconnected, causing the flash to fail and triggering DTC B169B-00. The ECU entered boot mode (flashing protection mode) and could not communicate via standard methods. Using a dedicated programming power supply to maintain stable voltage, the technician accessed engineering mode, re-flashed the underlying software, restored calibration data, and resolved the fault. This case emphasises that a regulated power supply must be used during flashing; power interruption is strictly prohibited.
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.