AU
B1698

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

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
5
Causes
Likely Causes — Seal U
  • 1SRS ECU internal hardware fault: internal processor damage, EEPROM data corruption, power management chip failure, or internal capacitor aging 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, corrosion on 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 faulty terminating resistor (120Ω) causing network failure.
  • 4Ignition circuit short circuit/open circuit: A 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 record 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) area overflow after a vehicle collision.
What To Do
  • 1
    Use VDS2000 or a dedicated BYD diagnostic tool to read the complete DTC list, record the freeze frame data, specifically check for accompanying U-class communication fault codes (such as U0151, U0164), and save data stream screenshots.
  • 2
    Check the SRS ECU power supply and ground: Disconnect the battery negative terminal for 3 minutes, then unplug the ACU connector (usually located under the centre console or behind the centre armrest box). Measure the voltage at Pin 30 (constant power B+) and Pin 28 (ignition power IG1); voltage must be 9-16V. Measure the resistance between Pin 24 (ground GND) and body ground; resistance must be <1Ω. Inspect the connector for water ingress, pin corrosion, or backed-out terminals.
  • 3
    Check CAN communication wiring: Measure resistance between diagnostic port pin 6 (CAN-H) and pin 14 (CAN-L). Resistance must be 60±5Ω (terminating resistor parallel value). Measure voltage to ground: CAN-H must be 2.5-3.5V and CAN-L must be 1.5-2.5V. Check wiring 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. The resistance must be >10MΩ. Inspect the steering wheel clock spring, the yellow connector under the seat, and the B-pillar connector for poor 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). Some models require crash sensor zero-point calibration.
  • 6
    System verification: Clear all fault codes, perform a system self-check (approx. 10 seconds), and confirm the SRS warning light turns off normally. Simulate ignition switch ON 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 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.