AU
B169D00

DTC B169D00 indicates the airbag control unit (SRS ECU/ACU) detects an internal systemic fault — Atto 8

Safety System

DTC B169D00 indicates the airbag control unit (SRS ECU/ACU) detects an internal systemic fault.

The ECU sets this code when it detects an abnormality in the processor core, non-volatile memory (NVM), safety sensor interface, or internal communication bus during the Power-on Self Test or cyclic monitoring.

As the core controller of the passive safety system, the SRS ECU monitors crash acceleration sensor signals in real time, processes crash algorithm decisions, and controls the firing circuits for the airbag modules and seat belt pretensioners.

This fault causes the ECU to enter Limp Home mode or fail completely.

Consequently, the ECU cannot correctly determine crash severity or trigger the corresponding protective devices during a collision, leading to airbags failing to deploy or deploying unintentionally.

This is an ASIL-D safety-critical fault.

Potential causes include ECU hardware damage, software runaway, abnormal supply voltage (below 9V or above 16V lasting beyond the set threshold), CAN/LIN communication physical layer faults, or system lockout resulting from a short or open circuit in the external crash sensor wiring.

The B169D00 fault code on the Atto 8 indicates an internal fault in the airbag control unit (SRS ECU), causing the system to enter limp mode or fail completely, risking improper airbag deployment. Severity is medium. Common causes include internal ECU hardware damage or power supply issues. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available based on 3 recorded cases.
3
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1SRS ECU internal hardware fault: damaged main control chip (e.g., Infineon TC2xx/TC3xx series MCU), memory (Flash/EEPROM) data checksum failure, or internal safety watchdog timeout
  • 2Power supply and ground system fault: unstable battery voltage (depleted battery or charging system fault); loose or oxidized dedicated SRS ECU ground points (G101/G102, etc.) causing excessive voltage drop; excessive contact resistance at the constant power (+B) circuit fuse.
  • 3Communication bus fault: Diagnostic CAN or private security CAN bus (CAN-H/CAN-L) short to power or ground, open circuit (common at the dashboard wiring harness connector), or terminating resistor drift (not the 60Ω standard value) compromising signal integrity.
  • 4Peripheral sensor circuit fault: Front impact sensor (FIS) or side impact sensor (SIS) wiring harness short to ground or power triggers the ECU protective lockout mechanism; water ingress into the sensor connector reduces insulation resistance.
  • 5Software and calibration faults: ECU firmware version defects, corrupted crash threshold calibration data, online configuration (Coding) data mismatch with vehicle VIN or hardware version, or data integrity check failure due to a previously interrupted flashing process.
What To Do
  • 1
    Perform a full system scan using the BYD VDS2000 or DMS diagnostic tool and record the B169D00 freeze frame data. Note the vehicle status when the fault occurred (ignition cycle, vehicle speed, supply voltage). Check for accompanying U-class communication fault codes (such as U0151 Lost Communication With SRS) or B13xx-class sensor fault codes.
  • 2
    Perform an SRS ECU software flash: Attempt to flash the latest ECU firmware via OTA or offline (usually located in the safety system flashing menu). If the flash interrupts or fails, directly diagnose an ECU hardware fault. After a successful flash, perform a key cycle test and observe if the fault code returns.
  • 3
    Power supply and ground verification: Disconnect the battery negative terminal for 3 minutes. Measure the voltage between SRS ECU connector terminal 30 (constant power +B) and ground (should be ≥12.4 V). Measure the ground point resistance (should be <0.1 Ω). Check the ground points in the engine compartment and under the instrument panel for tightness. If necessary, sand the mating surfaces and apply conductive grease.
  • 4
    Communication line inspection: Use an oscilloscope to measure the diagnostic CAN line (OBD Pin 6/14) waveform and check for abnormal spikes or level offsets. Measure the resistance between CAN-H and CAN-L (ignition switch OFF, ECU connector disconnected). Standard value: 60Ω±5Ω. Check the wiring harness for signs of crushing, abrasion, or water ingress. Focus on the harness junction point behind the instrument panel frame.
  • 5
    Sensor circuit check: If the above is normal, use the special tool to measure the continuity and insulation resistance of the crash sensor wiring. Check the wiring harness connectors at the front bulkhead, A-pillar and B-pillar for backed-out pins, oxidation or poor sealing, especially on accident-repaired vehicles.
  • 6
    ECU replacement and configuration: If the fault persists, replace the SRS ECU assembly. After installing the new ECU, perform online configuration (write the vehicle VIN, model code, and airbag configuration parameters). Read the system configuration to verify no discrepancies. Finally, perform an airbag system function test (use a dedicated resistor substitute; never directly measure the airbag igniter resistance).
Real-World Cases
BYD DTC AI Analysis

Qin EV: SRS warning light comes on intermittently while driving (communication interference type)

✓
A 2019 Qin EV developed intermittent SRS warning light illumination on the instrument cluster when driving over rough surfaces, which cleared following an ignition cycle. VDS scanning identified DTC B169D00 and intermittent U0151 (lost communication with SRS). Diagnosis revealed a non-genuine dashcam had been installed, with its power feed directly tapped into the SRS ECU supply fuse. This caused the voltage to drop to 8.2V during start-up, triggering the ECU low-voltage protection. Removed the unauthorised wiring, restored the factory fuse configuration, and cleaned the SRS ECU earth point. Fault resolved.
Original source ↗
BYD DTC AI Analysis

SRS ECU wiring harness pin backed out, causing intermittent fault on the E3 EV model.

✓
One week after delivery of a new 2020 BYD E3, the customer reported the SRS warning light constantly illuminated with DTC B169D00 stored. Inspection revealed the constant power pin (Pin 30) for the SRS ECU had backed out at the GJK14 instrument panel harness connector, causing intermittent ECU power. This connector, located behind the driver-side instrument panel reinforcement, was not fully latched during assembly and gradually loosened under vehicle vibration. After re-crimping the terminal and ensuring the connector lock engaged properly, the fault did not recur.
Original source ↗
BYD DTC AI Analysis

Hyundai model B169D00 (LIN communication error) reference case (applicable to BYD diagnostic logic)

✓
Although this case comes from Hyundai technical documentation (DTC B169D00: Right Rear Door Module [RRDM] LIN communication error), its diagnostic logic is highly relevant for troubleshooting LIN/CAN communication faults in BYD SRS systems. Measuring the LIN line resistance to ground revealed an open circuit, traced to a wiring harness fatigue fracture at the door hinge. For BYD SRS systems, similar physical layer faults—such as an open circuit in the LIN sub-bus between the ECU and crash sensors—can trigger B169D00-type communication faults. Focus continuity checks at harness bend points.
Original source ↗
Other Atto 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 overview →
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.