AU
B169E

B169E (SRS_ECU Fault) indicates the Airbag Control Unit (ACU) detected an internal circuit abnormality, a power supply/ground fault, or a critical communication bus interruption — Atto 3

Safety System

B169E (SRS_ECU Fault) indicates the Airbag Control Unit (ACU) detected an internal circuit abnormality, a power supply/ground fault, or a critical communication bus interruption.

This fault code signifies the SRS ECU cannot execute the self-test procedure, or it detected a functional failure in the internal processor, memory, or ignition loop monitoring circuit.

This is a Hard Fault, meaning the airbag system may be in a complete failure or degraded mode.

In a collision, the airbags or pretensioners may fail to deploy, posing a severe safety hazard.

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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1Abnormal SRS ECU power supply circuit: Includes a blown constant power (BAT+) fuse, poor contact at the IGN power relay, or loose or corroded ground points (G701/G702, etc.), causing the ECU operating voltage to drop below 9V or momentary power loss.
  • 2ECU internal hardware fault: Internal capacitor aging and leakage, main control chip (MCU) damage, ignition circuit driver transistor breakdown, or memory (EEPROM) data checksum failure.
  • 3CAN communication bus fault: Open or short circuit in the power CAN or dedicated safety CAN line between the SRS ECU and the vehicle gateway (GWM), or an abnormal terminal resistor (120Ω), causing a communication timeout.
  • 4Collision sensor interlock fault: An internal short circuit or short to ground in the front or side impact sensor causes the ECU to enter fail-safe mode to protect the ignition circuit and set an ECU fault.
  • 5Water ingress or physical damage: Vehicle wading causes ECU seal failure and water ingress, or vehicle accidents subject the ECU to mechanical impact or burn damage, resulting in internal circuit board corrosion or cracked solder joints.
What To Do
  • 1
    Safety Preparation and Initial Diagnosis: Disconnect the high-voltage system (execute the high-voltage power-down procedure for new energy vehicles). Use a dedicated diagnostic tool (VDS3000/BYD dedicated diagnostic tool) to read the complete fault code stream. Record whether B169E is a Current or History code. Check for accompanying B1650-B1680 series sensor faults.
  • 2
    Power supply and earth circuit check: Open the dashboard and locate the SRS ECU (usually under the centre console or in front of the gear selector). Measure the voltage between ECU connector terminal 30 (constant power), terminal 15 (IG power) and earth. Verify static voltage is ≥12 V and ≥10.5 V during start-up. Verify earth resistance is <1 Ω. Check fuses SB13 and SB14 (refer to the specific vehicle wiring diagram).
  • 3
    Communication bus inspection: Use an oscilloscope or multimeter to measure the diagnostic CAN bus (CAN-H and CAN-L) voltage (normally CAN-H ≈ 2.6V, CAN-L ≈ 2.4V) and resistance (with power off, terminating resistance should be approximately 60Ω; single ECU internal termination is 120Ω). Check the wiring for a short to ground or power.
  • 4
    ECU inspection and replacement test: Inspect the ECU housing for cracks, water stains, or burn marks. If the wiring is normal, perform an SRS ECU replacement test (requires a part with the same part number). After replacement, perform: ① Coding ② VIN writing ③ Crash Data Clear ④ System configuration and calibration.
  • 5
    System verification and road test: Clear all fault codes and perform the SRS system self-check cycle (turn the ignition switch to ON and observe if the SRS warning lamp turns off after the self-check); use the diagnostic tool to perform the 'Crash Sensor Test' and 'Ignition Circuit Test'; perform a road test to confirm the fault code does not recur, and verify the instrument panel SRS indicator status is normal.
Real-World Cases
BYD DTC AI Analysis

2020 BYD Tang DM B169E fault after wading through water

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Vehicle flooded to floor level. The next day the instrument cluster displayed 'SRS Fault'. The diagnostic tool read active DTCs B169E (SRS ECU Fault) and B1650 (Front Left Collision Sensor Communication Fault). Dismantling revealed the SRS ECU mounted beneath the floor. The housing seal had deteriorated, allowing water ingress, and the circuit board showed green corrosion. Replaced the ACU module, cleaned the corroded harness connectors, resealed and reinstalled the assembly, then performed coding matching and crash data reset. Fault resolved.
BYD DTC AI Analysis

2019 BYD Yuan EV ACU locked after accident repair

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Vehicle had a front-end collision. Airbags did not deploy; front bumper sustained damage. After repairs, fault codes were cleared but B169E would not erase. Analysis indicated the impact sensor generated a hard-coded signal from the shock, causing the ACU to enter a collision warning lock state. Inspection found the left front impact sensor's internal accelerometer damaged, outputting 0.2 V instead of the normal 2.5 V reference. Replaced left front impact sensor and SRS ECU (the ECU had logged the collision event and locked). Performed online coding and sensor zero-point calibration. System returned to normal.
BYD DTC AI Analysis

2021 BYD Qin Pro: Low-voltage battery drain causes abnormal ECU reset

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Customer reported the SRS light stayed on after jump‑starting the vehicle following long‑term storage. Diagnosis showed DTCs B169E (internal fault) and U0151 (loss of communication with SRS ECU). Battery voltage measured only 10.8V; the jumper cables had been connected with reversed polarity during the jump‑start. Low voltage and the reverse‑polarity voltage surge caused the SRS ECU internal memory data verification to fail. Replaced the 12V battery. Powered the system with a regulated 14V supply. Using the diagnostic tool, performed the ‘ECU Reset and Data Recovery’ procedure and updated the SRS software to the latest version (Ver 3.2.1). Cleared all fault codes. System self‑test passed.
BYD DTC AI Analysis

CAN bus interference caused by aftermarket modifications to BYD Song MAX

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After installation of a 360-degree panoramic camera system, the SRS warning light illuminated intermittently. We retrieved historical fault codes B169E and U1100 (CAN communication error). Inspection found the modification shop had spliced into the wiring to draw power from the OBD port, mistakenly connecting the CAN-H line in parallel with the airbag system’s dedicated CAN bus. This caused signal reflection and interference. We repaired the wiring harness, separated the modification device from the SRS system bus, and fitted ferrite core filters to the CAN lines. After clearing the faults, we monitored the vehicle for one month, and the issue did not recur.
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.