AU
B169A

DTC B169A indicates the airbag control unit (SRS ECU) detects an internal system fault or critical function failure — Atto 3

Safety System

DTC B169A indicates the airbag control unit (SRS ECU) detects an internal system fault or critical function failure.

This fault code typically indicates an abnormality in the ECU internal processor, memory, or power management module, forcing the airbag system into a degraded mode or complete failure state.

Specific symptoms include crash detection algorithm failure, ignition loop driver circuit faults, or interrupted communication with other safety modules (such as seatbelt pretensioners and crash sensors).

This fault directly prevents airbag deployment during a collision, disables seatbelt pretensioners, and continuously illuminates the instrument cluster airbag warning light.

On some models, this fault restricts Child Presence Detection (CPD) and smart key system functions, as these systems share sensor data or communication buses.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1SRS ECU internal hardware fault: main control chip (MCU) damage, EEPROM data corruption, internal capacitor aging, or ignition drive circuit short/open circuit.
  • 2Power supply system fault: Unstable constant power (+B) circuit voltage (below 9V or above 16V), loose or corroded ground terminal, or abnormal ignition switch signal causing ECU restart.
  • 3Communication bus fault: CAN-H and CAN-L line short/open circuit, terminating resistance deviation (not standard 60 Ω), LIN bus crash sensor communication timeout.
  • 4External equipment interference: Aftermarket accessories (dash cam, navigation unit) connected to the SRS circuit causing signal interference, or wiring harness connector corrosion after water ingress.
  • 5Software/data error: Defective ECU firmware version, lost crash threshold calibration data, or failure to perform Configuration Reset after repair, resulting in verification failure.
What To Do
  • 1
    Initial diagnosis: Use the BYD dedicated diagnostic tool (VDS2000/VDS6000) to read all DTCs. Confirm whether B169A is an active or history fault. Read the freeze frame data to record the vehicle status when the fault occurred.
  • 2
    Power supply and ground check: Measure the voltage at SRS ECU connector terminal +B (constant power) (standard: 11-14V), check the resistance at ground terminals G101/G102 (must be less than 1Ω), and confirm the IGN signal is at battery voltage with the ignition ON.
  • 3
    Communication line inspection: Disconnect the battery negative terminal for 3 minutes. Measure the resistance between diagnostic connector pin 6 (CAN-H) and pin 14 (CAN-L) (standard: 60Ω ± 2Ω). Check the CAN waveform at the SRS ECU terminal (recessive level 2.5V, dominant 3.5V/1.5V) to rule out a short or open circuit in the wiring.
  • 4
    Sensor and wiring harness inspection: Check the front impact sensor (FIS) and side impact sensor (SIS) connectors for water ingress or oxidation. Measure the sensor supply voltage (5V reference voltage). Check the wiring harness for crush damage causing a short to ground.
  • 5
    Software update and reset: If wiring is normal, update the SRS ECU software (if a newer version is available). Execute 'System Configuration' to write the vehicle VIN and configuration code. Execute 'Crash Data Clear' if crash data is present.
  • 6
    Component replacement and matching: If the above steps fail, replace the SRS ECU (verify the part number based on the vehicle model, e.g., 5A-3636100). Perform 'Online Matching' on the new ECU to disable the immobilizer, then perform 'Sensor Calibration' and a 'Deployment Test' (use a dedicated load instead of the airbag).
  • 7
    Final verification: Clear the fault code, perform a system self-check (3 ignition cycles), and confirm B169A does not return. Verify the instrument cluster airbag warning light turns off. Use the diagnostic tool to perform a 'Function Test' to simulate a crash signal and verify system response.
Real-World Cases
BYD DTC AI Analysis

2021 BYD Tang DM SRS ECU internal chip fault

✓
The dashboard displayed 'Check Airbag System'. Retrieved DTC B169A-00 (active). Inspection confirmed no accident history, but the vehicle had waded through water up to sill level. Removed the SRS ECU (located under the centre console) and found traces of oxidation on the circuit board. Replaced the ECU, but the fault persisted. Further inspection revealed both old and new ECUs could not communicate with the right-side impact sensor via the LIN bus. Found an internal short in the sensor causing a protective lockout in the ECU. Replaced the right B-pillar impact sensor and reconfigured the ECU. The fault cleared. Key point: B169A may be the result rather than the cause; inspect all peripheral devices.
BYD DTC AI Analysis

BYD Yuan EV 2019: Aftermarket equipment installation causing CAN bus interference

✓
Owner reported the airbag warning light occasionally flashing while driving. The diagnostic tool retrieved an intermittent B169A fault code. Inspection found the owner had installed an aftermarket dashcam powered from the SRS fuse. During startup, the device caused a voltage drop (to 8.5 V), resetting the SRS ECU. After removing the aftermarket device, rewiring the power feed to the ACC circuit, and using an oscilloscope to confirm no abnormal interference on the CAN bus, the fault did not return. Recommendation: Never tap power from SRS system circuits.
BYD DTC AI Analysis

BYD Qin Pro 2020 – Software Version Defect

✓
After accident repairs (replaced front bumper and left front sensor), the instrument cluster kept showing DTC B169A and the code would not clear. Found the replacement crash sensor was part number 5A-3636100 (Yuan EV specific), which had firmware incompatible with the required part number 5A-3636100B for the Qin Pro. After installing the correct part, the fault persisted. Ultimately, a BYD Technical Service Bulletin (TSB) confirmed that this batch of vehicles requires an SRS ECU software upgrade to version V2.3 to resolve the compatibility issue. After the upgrade, performed sensor ID registration and configuration write—the fault was resolved.
BYD DTC AI Analysis

2019 BYD Song MAX: Bad ground caused ECU reset

✓
The airbag warning light illuminated while driving on rough roads. Diagnosis revealed stored DTC B169A. Measured 0.8V voltage drop at SRS ECU ground terminal G102 (normal: less than 0.1V). Inspection found the ground point below the left A-pillar with a loose mounting bolt and paint on the contact surface. Sanded the metal surface at the ground point, re-tightened the bolt, and applied conductive grease. After a 200 km road test, the fault did not recur. Analysis: Poor grounding caused momentary power loss to the ECU during vibration, triggering internal fault protection.
BYD DTC AI Analysis

2020 BYD Han EV: Lockout due to uncleared accident data

✓
The vehicle had a minor rear-end collision. The airbags did not deploy, but DTCs B169A and B1650 (collision data stored) were retrieved. After the accident repairs, the fault codes could not be cleared. According to the BYD workshop manual, the SRS ECU may enter a locked state after recording a collision event, even without deployment. Using a diagnostic scan tool, the 'Crash Data Reset' and 'ECU Unlock' special functions were performed. After entering the manufacturer authorization code, the fault codes were successfully cleared and the system returned to normal. Note: This operation requires manufacturer authorization and confirmation that the ECU hardware has no physical damage.
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.