AU
B1698

DTC B1698 indicates the airbag system electronic control unit (ACU/SRS ECU) detects an internal system fault or critical function failure — Atto 3

Safety System

DTC B1698 indicates the airbag system electronic control unit (ACU/SRS ECU) detects an internal system fault or critical function failure.

This fault involves an ECU internal processor self-check anomaly, memory data checksum error, power supply monitoring circuit fault, firing circuit diagnostic system anomaly, or interrupted communication with the vehicle CAN network.

As the core control module of the passive safety system, the SRS ECU monitors crash sensor signals in real time and controls the firing circuits for multiple airbags and seat belt pretensioners.

When B1698 triggers, the system typically enters fail-safe mode and automatically disables all airbag and pretensioner deployment.

This causes a complete loss of vehicle crash protection capability and poses a severe safety hazard.

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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1SRS ECU internal hardware fault: Internal processor damage, EEPROM data corruption, power management chip failure, or aging internal capacitors causing unstable operating voltage.
  • 2Power supply system fault: battery voltage too low (<9V) or too high (>16V), poor connection in ECU constant power/ignition power circuit, poor contact at fuse F1/FB07, corroded ground wires G103/G303 causing increased contact resistance (>1Ω)
  • 3CAN communication bus fault: Interrupted communication with the Gateway Controller (GWC); CAN-H and CAN-L lines shorted to ground or power; wiring harness open circuit; or abnormal terminal resistor (120Ω) causing network failure.
  • 4Ignition circuit short/open circuit: Short to ground or short to power in the driver/passenger airbag, side airbag, seat belt pretensioner, or crash sensor wiring causes the ECU to trigger the protection mechanism and log an internal fault.
  • 5Software or calibration data corruption: control unit flashing failure, electromagnetic interference causing Flash data errors, long-term vibration causing memory bit flips, or Event Data Recorder (EDR) overflow after a vehicle collision.
What To Do
  • 1
    Use the VDS2000 or a dedicated BYD diagnostic tool to read the complete DTC list. Record the Freeze Frame data, specifically check for accompanying U-series communication fault codes (such as U0151, U0164), and save data stream screenshots.
  • 2
    Check SRS ECU power and ground: Disconnect the battery negative terminal for 3 minutes, then unplug the ACU connector (usually located under the center console or behind the center armrest). Measure voltage at Pin 30 (constant B+) and Pin 28 (ignition IG1). Voltage must be 9-16 V. Measure resistance between Pin 24 (ground GND) and body ground. Resistance must be <1 Ω. Inspect the connector for water ingress, pin corrosion, or backed-out terminals.
  • 3
    Check the CAN communication circuit: Measure the resistance between diagnostic connector pin 6 (CAN-H) and pin 14 (CAN-L). Resistance must be 60 ± 5 Ω (parallel value of terminating resistors). Measure the voltage to ground: CAN-H must be 2.5-3.5 V and CAN-L must be 1.5-2.5 V. Check the circuit continuity for ACU connector Pin 14 (CAN-H) and Pin 13 (CAN-L).
  • 4
    Check ignition circuit integrity: Use a multimeter to measure the insulation resistance to ground and power for each airbag, pretensioner, and crash sensor circuit. Resistance must be >10MΩ. Inspect the steering wheel clock spring, the yellow connector under the seat, and the B-pillar connector for loose connections or water ingress.
  • 5
    Perform ACU replacement and configuration: If the wiring is normal but the fault code will not clear, replace the SRS ECU with a unit of the same part number. Use VDS to perform online programming (write the VIN, vehicle configuration code, and calibration data). For applicable models, perform crash sensor zero-point calibration.
  • 6
    System verification: Clear all fault codes and perform a system self-check (approx. 10 seconds). Confirm the SRS warning lamp turns off normally. Simulate the ignition switch ON position and verify the ACU voltage, internal status, and crash sensor status in the data stream are normal. Perform a road test to confirm no intermittent faults.
Real-World Cases
BYD DTC AI Analysis

Internal corrosion in SRS ECU due to water wading

✓
Model: 2020 Song MAX 1.5T. Symptoms: After driving through heavy rain and floodwater, the instrument cluster displayed ‘Please check airbag system’. VDS read DTC B1698 (current and cannot clear). Diagnosis: Removed and inspected the ACU under the centre console. Found clear water staining and copper corrosion inside the connector, and the ECU housing seal had deteriorated. ACU power supply measured normal, but CAN bus voltage showed abnormal fluctuation. Repair: Replaced the ACU with a new assembly. Cleaned the harness connector terminals with electronic cleaner, applied conductive grease, and re-wrapped for waterproofing. After replacement, ran online programming and system self-test. Fault fixed.
BYD DTC AI Analysis

Poor ground connection after accident repair caused the fault.

✓
Vehicle: 2019 Yuan EV535. Symptom: SRS warning light remained illuminated after front collision repairs, and the system stored DTC B1698. Diagnosis: Checked ACU supply voltage at 12.4V (normal), but measured 8.5Ω resistance between the GND pin and body ground (abnormal). Inspection revealed that during accident repairs, the technician failed to properly reinstall the ACU ground wire after removing the centre console. Damaged threads on the ground bolt caused a poor connection. Repair: Retapped the ground stud and installed the ground wire using a new M6 bolt with serrated washer. Ground resistance dropped to 0.3Ω. Cleared DTCs, and the system returned to normal.
BYD DTC AI Analysis

Prolonged battery drain caused ECU initialization failure

✓
Model: 2021 Tang DM 2.0T. Symptom: Vehicle left unused for three months drained the battery. After a jump start, the SRS warning light came on. Codes B1698 and historical U0151 were retrieved. Diagnosis: Battery voltage measured only 8.2V, with severe fluctuations during the jump start (voltage spiked between 9–15V). Inspection found the ACU repeatedly failed to initialise under low voltage, logging internal fault codes. Repair: Fitted a new battery, used a regulated power supply to maintain 13.5V, cleared all DTCs, and performed the ACU restart sequence (power disconnected for over 10 minutes). The fault has not returned.
BYD DTC AI Analysis

Aftermarket modification caused CAN bus interference fault

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Vehicle: 2020 Qin Pro DM. Symptoms: After installing a large-screen aftermarket navigation system, the SRS system intermittently set DTC B1698; the fault appeared sporadically. Diagnosis: Checked ACU power and ground – normal. The CAN bus waveform showed significant noise. Inspection found the installer damaged the original SRS CAN harness shielding when pulling wires and did not twist the wires, causing interference from the audio amplifier’s high current. Repair: Repaired the damaged CAN wiring, restored the twisted-pair configuration (33–35 twists per metre), rewrapped the harness with aluminium foil shielding, grounded the shield at one end, and routed the harness away from the audio power cables. After the repair, the CAN waveform returned to normal and the fault cleared.
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.