AU
B169E-00

DTC B169E-00 indicates the airbag electronic control unit (SRS ECU/ACU) detected a fault during its internal self-check — Seal U

Safety System

DTC B169E-00 indicates the airbag electronic control unit (SRS ECU/ACU) detected a fault during its internal self-check.

Specifically, this constitutes a hardware or logic fault in the ACU internal processor, memory (EEPROM/Flash), power management module, or internal communication bus, rather than a problem with external sensors, wiring harnesses, or crash detection circuits.

This fault indicates the ACU cannot guarantee reliable execution of the airbag deployment logic during a collision, making it a safety-critical fault.

In BYD Qin series vehicles, the ACU typically mounts in the center tunnel or beneath the dashboard and manages multiple deployment circuits, including the front airbags, side curtain airbags, and seat belt pretensioners.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1ACU internal power management IC fault: Damaged internal voltage regulator chip causes abnormal power supply to the 3.3V or 5V logic circuit, triggering an internal watchdog reset failure.
  • 2EEPROM data corruption: Electromagnetic interference, voltage transients, or aging cause CRC check errors in memory configuration data, crash records, or calibration parameters.
  • 3Main control MCU crash or program runaway: ARM core processor enters an unrecoverable state due to abnormal clock signal, PCB cold solder joint, or software bug.
  • 4CAN transceiver physical layer fault: Damage to the CAN_H/CAN_L driver circuit inside the ACU interrupts vehicle network communication or causes error frame accumulation.
  • 5Temperature cycling causes BGA solder joint cracking: Prolonged high-temperature sun exposure (such as the installation position under the dashboard on Qin series models) causes micro-cracks in the main chip solder balls, resulting in intermittent poor contact.
What To Do
  • 1
    Use a dedicated diagnostic tool (such as BYD VDS or Launch X431) to read all fault codes. Check for B169E-00 and any accompanying U-series communication fault codes. Record the freeze frame data.
  • 2
    Perform an ACU power supply integrity check: measure constant power (B+, should be 12V±0.5V), ignition power (IGN, should be 12V at key ON), and ground (GND, resistance <1Ω) to rule out external power supply faults.
  • 3
    Inspect the CAN bus physical layer: Measure the resistance between OBD port pin 6 (CAN-H) and pin 14 (CAN-L) (should be approximately 60 Ω; the Qin series typically uses dual terminating resistors), and check the waveform for interference.
  • 4
    Attempt software recovery: If the vehicle supports online flashing, upgrade the ACU control unit software version or reflash it (back up the original coding data) and observe if the fault code clears.
  • 5
    Power-off reset procedure: Disconnect the battery negative terminal for more than 5 minutes. Disconnect the ACU connector (usually at the front of the centre tunnel or behind the glovebox) and inspect the pins for oxidation. Reconnect and test.
  • 6
    Replace the ACU assembly: If the fault persists, replace the airbag control unit with one matching the original part number (ACU part numbers for Qin EV300/450 and Qin DM/petrol versions may differ; check the configuration table).
  • 7
    Perform coding matching: Use the diagnostic tool to write the vehicle VIN and vehicle configuration code (such as number of airbags, seat belt type, and presence of knee airbags), and set the crash threshold parameters.
  • 8
    Complete system self-check: Perform 'Airbag System Configuration', 'Crash Sensor Calibration', and 'All Ignition Circuit Resistance Test'. Confirm no new fault codes appear and the instrument cluster airbag warning lamp turns off after the self-check.
Real-World Cases
BYD DTC AI Analysis

Qin EV300 ACU internal memory verification failed

✓
A 2017 Qin EV300 with 60,000 km had the airbag warning light constantly on. VDS read DTC B169E-00. Power supply, ground and CAN lines were normal. Offline ACU software refresh failed with 'Internal Memory Check Error'. Replaced the ACU (part number BC-5820100), performed 'ECU Coding' to write the vehicle configuration (Qin EV300 with side curtain airbags), and performed 'Crash Sensor Initialization'. Fault resolved. Analysis of the returned old part confirmed an internal EEPROM page write error.
BYD DTC AI Analysis

Jump-starting the Qin 100 caused ACU overvoltage damage

✓
2017 BYD Qin 100 had a flat battery. The owner performed an incorrect jump start using a 24V truck battery, causing the airbag warning light to illuminate. Diagnosis revealed DTC B169E-00 accompanied by multiple U-class communication faults. Measuring the ACU power input showed the internal protection diode had broken down; the ACU sustained physical damage. After replacing the ACU, inspection revealed that overvoltage had also damaged the front impact sensor (mounted on the front side member). Replaced both the front impact sensor and the ACU, performed 'System Configuration' and 'Sensor Learning', and the system returned to normal.
BYD DTC AI Analysis

Qin EV450 ACU software version defect

✓
The 2018 Qin EV450 started throwing DTC B169E-00 occasionally after a BMS software upgrade. The vehicle had no collision history. The shop found the ACU software was an early version (V1.02) with a bug causing CAN communication conflicts under certain conditions. They confirmed the issue via a BYD technical service bulletin and upgraded the ACU software to V1.05. After clearing the fault codes and doing several test drives, the fault did not recur. This is a software fault—no hardware replacement needed.
BYD DTC AI Analysis

High temperatures caused cold solder joints in the ACU on the BYD Qin 80.

✓
In Hainan, a 2017 BYD Qin 80 experienced intermittent airbag warning light illumination during summer. DTC B169E-00 was stored as a history code. The fault did not occur when cold but reappeared when hot (after sun exposure). Disassembled the ACU and found cold solder joints on the BGA connections of the main control chip (Freescale series). To repair, reball and resolder the BGA connections using a BGA rework station, or replace the ACU. Also check whether the thermal insulation under the dashboard has detached to improve the ACU's cooling environment.
BYD DTC AI Analysis

Replaced ACU without coding; fault persisted.

✓
The workshop replaced the ACU on an accident-damaged Qin EV300, but DTC B169E-00 remained. They found the new ACU was blank — no vehicle configuration data had been written. Using VDS, they performed 'Airbag System Configuration', selected the correct model (2017 Qin EV300 with 6-airbag configuration), wrote the VIN, and carried out 'ECU Online Matching' (requires connection to BYD server for authorization). After completing, they ran 'System Self-Check' and the fault code cleared successfully.
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.