AU
B1698

DTC B1698 indicates the airbag system electronic control unit (ACU/SRS ECU) detects an internal system fault or critical function failure — Atto 8

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.

The B1698 fault code on the Atto 8 indicates an internal fault in the airbag control unit (SRS ECU), such as a processor error, memory corruption, or power supply issue. This is a medium severity fault that disables all airbags and seat belt pretensioners, creating a serious safety risk. Common causes include ECU hardware failure or voltage problems. You should visit an authorised dealer for repair. Typical repair cost data is available based on 4 recorded cases.
4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1SRS ECU internal hardware fault: damaged internal processor, corrupted EEPROM data, failed power management chip, or aged internal capacitors causing unstable operating voltage.
  • 2Power supply system fault: battery voltage too low (<9V) or too high (>16V), loose connection in the 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: Network failure caused by interrupted communication with the Gateway Controller (GWC), CAN-H and CAN-L lines shorted to ground or power, an open circuit in the wiring harness, or an abnormal terminating resistor (120Ω).
  • 4Ignition circuit short/open: 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) area overflow after a vehicle collision.
What To Do
  • 1
    Use the VDS2000 or BYD dedicated diagnostic tool to read the complete DTC list and record the freeze frame data. Check specifically for accompanying U-class communication fault codes (such as U0151, U0164) and save screenshots of the data stream.
  • 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 box). Measure the voltage at Pin 30 (constant power B+) and Pin 28 (ignition power IG1); the voltage should be 9-16V. Measure the resistance between Pin 24 (ground GND) and body ground; the resistance should be <1Ω. Check the connector for water ingress, pin corrosion, or backed-out pins.
  • 3
    Check the CAN communication circuit: Measure the resistance between diagnostic connector pin 6 (CAN-H) and pin 14 (CAN-L). The 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 circuit continuity between 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 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 lamp turns off normally. Simulate the ignition switch in the ON position and check the data stream to verify the ACU voltage, internal status, and crash sensor status are normal. Perform a road test to confirm no intermittent faults exist.
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 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 overview →
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.