AU
B1698-00

B1698-00 indicates the airbag system electronic control unit (SRS ECU) detects an internal fault or critical function abnormality — Atto 3

Safety System

B1698-00 indicates the airbag system electronic control unit (SRS ECU) detects an internal fault or critical function abnormality.

This fault code typically indicates an SRS ECU internal memory error, processor fault, power supply voltage out of operating range (overvoltage or undervoltage), or a persistent communication bus fault between the ECU and the crash sensors or airbag modules.

In BYD Qin series vehicles, this fault forces the airbag system into fail-safe mode and continuously illuminates the instrument panel airbag warning lamp.

During a collision, the vehicle may fail to deploy the airbags and seat belt pretensioners, posing a severe safety hazard.

This fault code is a hard fault that does not clear automatically and requires professional diagnosis and repair.

3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Abnormal SRS ECU power supply circuit: unstable battery voltage, blown fuse (e.g., dedicated SRS fuses F1/14, F1/15), poor power supply circuit connection, or excessive voltage drop.
  • 2Poor ground connection: The SRS ECU ground terminal (usually located on the instrument panel frame or lower A-pillar) is loose, oxidized, or corroded, causing excessive ground resistance (standard: < 1Ω).
  • 3SRS ECU internal hardware fault: internal capacitor aging, memory data corruption, microprocessor malfunction (common in early-batch 2017-2018 Qin series models).
  • 4CAN bus communication fault: A short circuit, open circuit, or electromagnetic interference in the communication line between the SRS ECU and the vehicle CAN network prevents normal ECU operation.
  • 5External sensor or actuator short circuit: Internal short circuit in the front crash sensor, side airbag sensor, or airbag module pulls down the SRS ECU reference voltage and triggers the ECU protective fault code.
What To Do
  • 1
    Safety check and preliminary inspection: Disconnect the high-voltage manual service disconnect (MSD) and wait 5 minutes for the high-voltage system to discharge. Disconnect the 12V battery negative terminal and wait at least 3 minutes for the SRS capacitor to discharge fully, preventing accidental airbag deployment.
  • 2
    Visual inspection: Check the SRS ECU for physical damage, water stains, or burn marks. Check the SRS ECU wiring harness connector (usually 24-48 pins) located under the dashboard or in the center tunnel for looseness, backed-out terminals, or corrosion.
  • 3
    Power and ground measurement: Reconnect the battery and turn the ignition switch to the ON position. Use a multimeter to measure the voltage at the SRS ECU connector power terminals (constant power +B and ignition switch IG wire). The voltage should be 11-14V. Measure the resistance between the ground terminal and body ground. The resistance should be less than 1Ω.
  • 4
    Deep diagnostic scan: Use a BYD VDS or Launch X-431 diagnostic tool to access the SRS system. Read the complete freeze frame data to confirm if B1698-00 is a stored or current code. Check for accompanying communication fault codes (such as U-codes).
  • 5
    Wiring harness continuity test: Disconnect the SRS ECU and crash sensor connectors. Measure the continuity and insulation of the CAN-H, CAN-L, and sensor power wires between them. Confirm no short to ground or short to power. Wiring harness resistance must be less than 2Ω.
  • 6
    Software and configuration check: Verify the SRS ECU software is the latest version. Compare against the BYD Technical Service Bulletin (TSB). Update the software or reconfigure the coding if necessary.
  • 7
    Component Replacement and Verification: If all above checks are normal, replace the SRS ECU with the same part number (Note: older Qin series ECUs may require VIN coding). After replacement, perform the airbag system self-check cycle test to confirm the fault code does not return and the airbag warning light turns off normally.
Real-World Cases
BYD DTC AI Analysis

Qin EV300 airbag warning light suddenly came on while driving.

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Vehicle: 2017 Qin EV300, 42,000 km, no accident history. Symptoms: Airbag warning light suddenly illuminated during normal driving. VDS read DTCs B1698-00 (SRS ECU fault) and B1694-00 (power supply voltage low). Diagnosis: Measured SRS ECU power supply terminals and found IG power voltage fluctuating between 8.5V and 11V — abnormal. Traced the wiring harness and discovered a loose harness retaining clip under the dashboard. The harness had been rubbing against the steering column metal bracket over time, damaging the insulation and partially breaking the copper wires, causing high resistance. Repair: Repaired the damaged harness, re-secured the harness routing, and measured voltage restored to 12.4V. Cleared fault codes, the airbag light went out, and the system returned to normal.
BYD DTC AI Analysis

BYD Qin 100 SRS failure after wading though water

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Vehicle: 2017 BYD Qin 100. After driving through heavy rain and floodwater, the instrument cluster displayed "Check Airbag System." Symptoms: The vehicle waded through approximately 30 cm of water. The airbag warning light then stayed on constantly. The scan tool showed active fault code B1698-00. Diagnosis: Removed the SRS ECU from beneath the centre console. The ECU housing seal had deteriorated, with visible water stains and oxidation on the circuit board. Measured ECU power supply: normal, but the internal CAN transceiver pins were shorted to earth. Solution: Fitted a new SRS ECU (part number: BYDEG-3658100). Replaced the wiring harness seal. Dried and applied corrosion protection to the surrounding wiring harness. Performed ECU coding. Fault resolved.
BYD DTC AI Analysis

Intermittent B1698-00 fault on Qin EV450

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Vehicle: 2018 Qin EV450. Fault intermittent, more likely during cold starts. Symptoms: The airbag warning light occasionally came on during morning startup and sometimes went off after driving for a while. VDS scan showed historic DTC B1698-00. Diagnosis: During continuous monitoring, I found the SRS ECU earth voltage was 1.2V when the fault occurred (normal: <0.1V). I inspected the earth wire and found the earth point beneath the A-pillar. The mounting bolt was loose, and the contact surface had paint and oxidation. Repair: I sanded the earth point contact surface to bare metal, reinstalled the earth bolt, and tightened it to standard torque (typically 8-10N·m). Earth resistance dropped to 0.3Ω after the repair. I monitored the vehicle for a week; the fault did not return.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.