AU
B169D-00

DTC B169D-00 indicates the airbag control unit (SRS ECU) detects an internal fault or abnormal system communication — Seal U

Safety System

DTC B169D-00 indicates the airbag control unit (SRS ECU) detects an internal fault or abnormal system communication.

This ECU is the core control module of the airbag system.

It monitors crash sensor signals, determines crash severity, controls the deployment timing of the airbags and pretensioners, and records crash data (EDR).

Faults in the ECU internal processor, memory, or power management circuit, interrupted communication with the vehicle CAN network, or data checksum errors trigger this fault code.

This fault may cause the airbag system to enter fail-safe mode, preventing normal airbag deployment during a collision and severely compromising occupant passive safety protection.

This is a critical safety-related fault.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal hardware fault: Damage to the control module internal CPU, memory chip, or power voltage regulation circuit causes the self-check program to fail.
  • 2Power supply and ground fault: Unstable voltage or excessive voltage drop in the constant power (+BAT) or ignition power (+IG) supply, or ground harness contact resistance exceeding specifications (>10Ω), causing abnormal ECU power supply.
  • 3CAN bus communication fault: Short circuit, open circuit, or abnormal terminal resistance (normally 60 Ω in parallel) in the CAN-H/CAN-L lines between the SRS ECU, vehicle gateway, and instrument cluster interrupts data exchange.
  • 4Wiring harness connector issue: ECU connector water ingress and oxidation, terminal back-out, or poor contact, especially after vehicle wading or washing.
  • 5Software or data corruption: Abnormal internal ECU calibration data, abnormal crash threshold parameters, or software version defects cause the system to falsely indicate a hardware fault.
What To Do
  • 1
    Use the BYD VDS2000 or Launch X431 diagnostic tool to access the SRS system, read and record all DTCs and freeze frame data, and confirm B169D-00 is a current fault (Active) rather than a history fault.
  • 2
    Check the SRS ECU appearance and installation condition. Confirm no physical damage or signs of water ingress. Check the wiring harness connector (usually located under the center console or center tunnel) for looseness, water ingress, or oxidized pins.
  • 3
    Measure the ECU power supply voltage: Use a multimeter to verify the +B terminal (constant power) voltage is 12.0-14.5V, the +IG terminal (ignition ON) voltage matches battery voltage, and the ground terminal to vehicle body resistance is <1Ω.
  • 4
    Check the CAN communication circuit: Disconnect the ECU connector. Measure CAN-H and CAN-L voltage to ground (normal: approx. 2.5V). Measure the resistance between the two lines (normal: 60Ω ± 5Ω, due to parallel 120Ω terminating resistors). Check for short or open circuits.
  • 5
    Perform software diagnostics: Reflash or upgrade the SRS ECU using the BYD dedicated diagnostic tool and the latest software package to eliminate false reports caused by software defects.
  • 6
    Replace the SRS ECU: If wiring measurements are normal and the software flash fails, replace the airbag control module (verify the part number by vehicle model, e.g., Qin EV450 is...). After replacement, perform coding and immobilizer matching.
  • 7
    System calibration and testing: After replacing the ECU, perform the crash sensor zero-point calibration, seat belt pretensioner and airbag circuit resistance tests, and finally a simulated crash signal test (using the special tool). Confirm the fault code clears and the instrument cluster airbag warning light turns off.
Real-World Cases
BYD DTC AI Analysis

Qin EV300 intermittent SRS ECU fault after water wading

✓
A 2017 Qin EV300 presented with an intermittent 'Check SRS System' warning on the instrument cluster, along with intermittent DTC B169D-00. Investigation revealed the vehicle had been driven through flood water. The SRS ECU is located beneath the centre tunnel; upon disassembly, water staining was found inside the ECU connector and minor oxidation on the pins. Cleaning the connector and applying conductive paste temporarily cleared the fault, but it returned after one week. Measurement identified corrosion on the ECU ground wiring harness following water ingress, causing contact resistance to increase to 15Ω. Replacing the ground wiring harness and resealing the connector permanently resolved the fault.
BYD DTC AI Analysis

Qin 100 B169D-00 fault after accident repair

✓
After front collision repairs on a 2017 Qin 100, the airbag warning light stayed on, storing DTC B169D-00. Inspection found the front impact sensor wiring harness had been damaged in the crash. The repair shop used a non-genuine harness, causing CAN bus signal interference. The SRS ECU detected the communication fault and triggered a protective fault. Replaced the front impact sensor harness with a genuine part, confirmed no noise on the CAN bus waveform, cleared the DTCs, and the system returned to normal.
BYD DTC AI Analysis

Qin EV450 software version defect causes false positive

✓
A 2018 BYD Qin EV450 developed a B169D-00 fault code after a service. The vehicle had no collision history, and a wiring inspection found no abnormalities. Using a VDS diagnostic tool, technicians found the ECU was running an early software version (V1.02) with a known self-check logic defect. They upgraded the ECU software to V1.05, which cleared the fault code automatically. The fault has not returned. This software issue is common in some 2018 production batches. Resolve it via an OTA update or a dealer visit for the software upgrade.
BYD DTC AI Analysis

Battery discharge caused abnormal SRS ECU voltage

✓
A long-parked Qin 80 had a severely discharged battery (voltage <9V). After a jump start, multiple warning lights illuminated on the dashboard, including the airbag light. The scan tool retrieved DTC B169D-00. The ECU self-check had failed due to the low voltage. We fully charged the battery (voltage restored to 12.8V) and cleared the codes; the fault did not return. We recommended the owner check the battery State of Health (SOH) to prevent false ECU faults from voltage instability.
BYD DTC AI Analysis

ECU incompatibility fault after aftermarket airbag replacement

✓
A workshop replaced the driver airbag on a Qin EV300 with an aftermarket unit. Afterwards, the instrument cluster airbag warning light came on and the system stored DTC B169D-00 along with multiple airbag circuit faults. The shop found the aftermarket igniter resistance was 1.2 Ω, while the OEM specification is 2.0 Ω ± 0.3 Ω, causing the ECU to detect a system fault and activate protection mode. After installing a genuine driver airbag, the technician used a scan tool to run the 'replace airbag component' reset procedure. The fault codes cleared and the system returned to normal operation.
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.