AU
B1697

DTC B1697 indicates the airbag control unit (SRS ECU) detected an internal hardware fault or critical support circuit error, forcing the system into fail-safe mode — Seal U

Safety System

DTC B1697 indicates the airbag control unit (SRS ECU) detected an internal hardware fault or critical support circuit error, forcing the system into fail-safe mode.

This fault involves an internal microprocessor calculation error, EEPROM data corruption, an abnormal internal accelerometer signal, an ignition driver circuit fault, or a severe fault in the external power supply, ground, or communication lines.

When triggered, the SRS ECU disables deployment of all airbags and seat belt pretensioners.

The vehicle provides no passive safety protection during a collision.

This severe fault compromises driving safety.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal hardware fault: Functional failure due to main control chip (MCU) damage, internal memory data checksum failure, swollen capacitors, or cold solder joints.
  • 2Abnormal power supply: Poor connection or unstable voltage in the constant power (B+) circuit, poor contact in the ignition switch power (IG1) circuit, or oxidation in the dedicated fuse socket (usually 10A-15A) interrupting the power supply.
  • 3Ground system fault: Corroded SRS ECU ground terminals (G101/G102), broken ground wiring harness, or excessive contact resistance (>1Ω), causing control unit reference voltage drift.
  • 4CAN bus communication fault: Communication interruption due to a short to ground or power in the powertrain CAN or chassis CAN wiring, a short between CAN-H and CAN-L, an open circuit, or an abnormal terminating resistor (120Ω).
  • 5Environmental and physical damage: Control unit housing seal failure causing water ingress and moisture, ECU internal acceleration sensor damage following a vehicle accident, prolonged high-temperature exposure causing internal component aging.
What To Do
  • 1
    Fault Confirmation and Data Recording: Use the BYD dedicated diagnostic tool (VDS2000 or Launch X431) to read the complete DTC list. Record the B1697 freeze frame data. Determine if the fault is current or historical. Observe if the instrument panel SRS warning light is solid or flashing.
  • 2
    Power and ground circuit inspection: Disconnect the battery negative terminal and wait 90 seconds (for capacitor discharge). Unplug the SRS ECU connector. Measure the voltage at the power supply terminals (constant power and IG power) (standard value: 11-14V; 13.5-14.5V with the engine running). Measure the resistance between the ground terminal and body ground (should be <1Ω). Check the connector pins for oxidation or push-out.
  • 3
    Communication line diagnosis: Measure the resistance between CAN-H and CAN-L at the diagnostic connector (OBD) or the SRS ECU connector (standard value: approximately 60Ω, two 120Ω terminating resistors in parallel). Measure the resistance of each CAN line to ground and to power (should be >1MΩ). Use an oscilloscope to check the CAN waveform for distortion.
  • 4
    Detailed wiring harness and connector inspection: Inspect the airbag wiring harness for wear or crush marks. Specifically check the airbag clock spring under the steering wheel for short circuits. Check the side airbag wiring harness connector under the seat for looseness (frequent seat adjustment easily damages this connector).
  • 5
    Software diagnosis and reflashing: Check the SRS ECU software version number and consult the BYD Technical Service Bulletin (TSB). If a software defect exists, perform an ECU software upgrade (reflash) or rewrite configuration parameters (coding). Some models require crash sensor zero-point calibration.
  • 6
    Control unit replacement and matching: If all above checks are normal, replace the SRS ECU with one of the same part number. Perform Online Coding, enter the vehicle VIN and configuration code, perform a System Check, and clear the fault codes. Perform an airbag simulated deployment test (using the special tool) to confirm normal system operation.
Real-World Cases
BYD DTC AI Analysis

Intermittent SRS ECU fault in 2021 Tang DM caused B1697

✓
A Tang DM with 32,000 km on the clock. The SRS warning light illuminated intermittently on the dash. The scan tool retrieved DTC B1697, alternating between current and stored. Inspection found the SRS ECU supply voltage fluctuating between 13.2V and 11.8V. Traced the power feed from the battery positive terminal to the SRS ECU and found the wiring harness had worn through at the engine bay fuse box from vibration, causing a poor connection. Repaired the harness and secured the routing. Fault cleared.
BYD DTC AI Analysis

2019 BYD Song MAX: CAN bus short circuit caused SRS system failure

✓
After driving through water, DTC B1697 set and the SRS warning light stayed on. Measurement found CAN-H shorted to ground (only 2Ω). Disassembly revealed a poorly sealed waterproof plug on the wiring harness below the left A-pillar, allowing water ingress that corroded and shorted the CAN circuit. Cleaned the corroded harness, replaced the SRS ECU (water had already caused internal damage), and reapplied waterproofing to resolve the fault.
BYD DTC AI Analysis

2019 BYD Yuan EV: SRS ECU internal memory failure

✓
During normal driving, the vehicle suddenly displayed an airbag fault. Retrieved DTC B1697, which would not clear. Checked the power supply, ground and communication circuits – all normal. Attempted a software upgrade, but it failed. Disassembled the SRS ECU and found cracked solder joints on the internal EEPROM chip (stores crash threshold and configuration data). Since this chip is encrypted, it cannot be replaced separately. Replaced the complete SRS ECU, performed online matching, and the system returned to normal.
BYD DTC AI Analysis

2020 Qin Pro DM software fault causing false B1697 alert

✓
Found B1697 DTC during new vehicle PDI, but SRS warning light remained off. Inspected hardware, no faults. Checked TSB and identified an SRS software bug in this production batch causing false ECU failure reports under specific voltage conditions. Upgraded software to V2.3.5, cleared fault code, and it did not return. This is a typical software calibration issue.
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.