AU
B169A-00

B169A-00 indicates an internal fault in the airbag control unit (SRS ECU) or a system-level communication fault — Atto 3

Safety System

B169A-00 indicates an internal fault in the airbag control unit (SRS ECU) or a system-level communication fault.

The SRS ECU is the core control module of the vehicle’s passive safety system, responsible for monitoring crash sensors, controlling airbag deployment, triggering seat belt pretensioners, and recording crash data.

This fault code indicates the ECU self-check detected an internal processor fault, memory checksum failure, internal bus communication interruption, or critical circuit abnormality.

This fault constitutes a serious safety hazard; it may prevent the airbag system from deploying correctly during a collision or cause unintended deployment.

In BYD Qin series vehicles, the SRS ECU typically mounts beneath the center console or in the central armrest area, communicating with the vehicle network via the CAN bus.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1SRS ECU internal hardware fault: Damaged microprocessor, EEPROM memory chip, or internal power supply circuit causing self-test failure.
  • 2Power supply system fault: battery voltage too low (below 9V) or too high (above 16V), blown SRS dedicated fuses (ECU-B, AIR BAG), or loose or oxidized ground terminal.
  • 3CAN bus communication fault: Short circuit or open circuit in the CAN-H and CAN-L lines, or abnormal terminating resistance, interrupts communication between the ECU and the vehicle network.
  • 4External physical damage: Vehicle driven through water, water ingress or moisture at the ECU mounting position causing circuit board corrosion, or ECU internal acceleration sensor damage following a vehicle accident.
  • 5Peripheral component short circuit: Internal short circuit in the clock spring (spiral cable), crash sensor, or seat occupancy recognition sensor triggers an ECU protective fault.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS or ED400) to read all fault codes. Check for accompanying U-series communication fault codes (such as U0151, U0164) and historical freeze frame data.
  • 2
    Check the vehicle battery voltage (static voltage ≥12.4V; 13.5-14.5V after startup). Check if the SRS system fuse in the dashboard fuse box (usually labeled SRS, AIR BAG, or ECU-B) is blown.
  • 3
    Locate the SRS ECU (on Qin series models, it is usually under the lower center console; remove the auxiliary instrument panel). Check the connector for looseness and the pins for oxidation or water ingress. Measure the ground point resistance (<1Ω).
  • 4
    Measure voltage at the SRS ECU power supply terminals (constant power B+, ignition power IG) and the CAN bus (CAN-H approx. 2.6–2.8 V, CAN-L approx. 2.2–2.4 V, resistance approx. 60 Ω).
  • 5
    Disconnect the negative battery terminal, wait 3 minutes, and attempt to clear the fault code. Power on the vehicle and perform the SRS system self-check. If the fault code persists or reappears immediately, replace the SRS ECU control unit.
  • 6
    After replacing the ECU, perform online programming (Coding), write the vehicle model configuration, and calibrate the system. Use the diagnostic tool to perform the 'Collision Output Test' to verify normal system function.
Real-World Cases
BYD DTC AI Analysis

Qin EV450 SRS ECU internal processor fault

✓
The airbag warning light stayed on constantly during normal driving, with no accident history. Used VDS to read fault code B169A-00, with no accompanying communication fault codes. Checked the ECU connector and found no loose connections; supply voltage at 12.6V was normal, and CAN bus waveform was normal. Diagnosed as an intermittent internal microprocessor fault in the ECU. Replaced the SRS ECU and programmed it. Fault cleared and the airbag warning light went out after self-check.
BYD DTC AI Analysis

Qin 100: Low auxiliary battery voltage caused system low voltage fault

✓
After extended parking, the battery drained and the vehicle would not start. Following a jump-start, the airbag warning light came on and stayed on. The diagnostic tool read codes B169A-00 and B1620-00 (backup power supply fault). Inspection found the original battery had only 28% life remaining; voltage instability caused the ECU self-check to fail. Replaced the battery, cleared the fault codes, and performed three ignition cycle self-checks. The SRS system returned to normal and the fault has not reappeared.
BYD DTC AI Analysis

BYD Qin EV300 ECU corrosion fault after water ingress

✓
After driving through standing water, the airbag warning light illuminated. Fault code B169A-00 retrieved. Disassembly revealed the SRS ECU installed under the central tunnel. Blocked drain holes caused water to accumulate and submerge the unit, leaving clear corrosion on the circuit board. Replaced the SRS ECU, drained the water from the central tunnel, cleared the drain holes, and treated oxidation on the wiring harness connectors to resolve the fault. Recommend checking under the carpet for other modules that may also be at risk of water ingress.
BYD DTC AI Analysis

Aftermarket modification caused CAN bus interference fault

✓
After the owner installed an aftermarket large-screen navigation system, the airbag warning light stayed on constantly with DTCs B169A-00 and U0151 (lost communication with SRS) stored. Inspection found the installer had mistakenly connected the SRS CAN lines in parallel with the entertainment system CAN lines while splicing into the CAN wiring, causing abnormal bus loading. After restoring the original wiring harness connections and fitting an isolation gateway, SRS communication returned to normal, and the fault did not recur after clearing the codes.
BYD DTC AI Analysis

Clock spring short circuit triggered ECU protective fault

✓
The airbag warning light illuminated after abnormal steering wheel movement, with DTC B169A-00. Inspection found the clock spring (spiral cable) beneath the steering wheel had developed an internal short from prolonged wear, with resistance measuring 0.3 Ω (normal range: 2–5 Ω). The short-circuit current triggered the SRS ECU protection mode. Replaced the clock spring, inspected the airbag harness (no damage), cleared the fault codes, and the system returned to normal.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.