AU
B169A-00

B169A-00 indicates an internal fault in the airbag control unit (SRS ECU) or a system-level communication fault — Atto 8

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 8
  • 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), dedicated SRS fuse (ECU-B, AIR BAG) blown, or ground terminal loose or oxidized.
  • 3CAN bus communication fault: Short circuit, open circuit, or abnormal terminal resistance in the CAN-H and CAN-L lines, interrupting communication between the ECU and the vehicle network.
  • 4External physical damage: Vehicle wading, water ingress or moisture at the ECU mounting position causing circuit board corrosion, or internal ECU 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 a protective ECU fault.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS or ED400) to read the complete 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 starting). 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 center console; remove the auxiliary instrument panel). Inspect the connector for looseness and the pins for oxidation or water ingress. Measure the ground point resistance (must be <1Ω).
  • 4
    Measure the SRS ECU power supply terminals (constant B+, ignition power IG) and CAN bus voltage (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 and wait 3 minutes. Reconnect power, attempt to clear the fault code, and perform an SRS system self-check. If the fault code fails to clear 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 8 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.