AU
B1699

DTC B1699 indicates an internal self-check fault in the airbag system Electronic Control Unit (SRS ECU) — Atto 3

Safety System

DTC B1699 indicates an internal self-check fault in the airbag system Electronic Control Unit (SRS ECU).

As the core control module of the passive safety system, the SRS ECU integrates acceleration sensors, safing sensors, ignition driver circuits, and a microprocessor.

This DTC triggers when the ECU detects an internal processor fault, memory data checksum error, internal communication bus anomaly, or power management module fault during the self-check.

The airbag system enters fail-safe mode, meaning the airbags and seat belt pretensioners may fail to deploy during a collision.

The instrument panel SRS warning light illuminates continuously.

External power supply or ground faults typically trigger specific DTCs such as B1693 (poor ground) and B1694/B1695 (abnormal supply voltage).

DTC B1699 specifically indicates an internal circuit fault within the ECU itself.

3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Hardware damage to the SRS ECU main control chip, memory, or ignition drive circuit, common in older vehicles or vehicles exposed to strong electromagnetic interference.
  • 2Abnormal ECU supply voltage (battery voltage continuously exceeding 16V or falling below 9V) causes internal power management module breakdown or protection circuit latching.
  • 3During a previous vehicle collision, the ECU internal acceleration sensor detected an impact but the airbag did not deploy, locking the internal diagnostic circuit or physically damaging the sensor.
  • 4Extreme environmental conditions (high temperature, high humidity, wading) cause internal ECU circuit board corrosion, cold solder joints, or bulging capacitors, affecting signal processing accuracy.
  • 5Software data corruption or interrupted flashing causes ECU firmware checksum failure, preventing the initialization self-check from completing.
What To Do
  • 1
    Connect the BYD dedicated diagnostic tool (VDS or ED400). Enter the SRS system to read all fault codes and freeze frame data. Verify B1699 is a current fault and the only code present. Rule out any accompanying communication or sensor faults.
  • 2
    Check the SRS ECU power supply circuit: Measure the voltage from connector G36 pin 35 (constant power +B) to ground; it must be battery voltage. Pin 34 (IG1 power) must be 12V with the ignition ON. Check fuse F4/9 and related relays.
  • 3
    Check the ECU ground circuit: Measure resistance between G36-35 and body ground. Resistance must be less than 1 Ω. Inspect ground point G109 for oxidation or looseness.
  • 4
    Check the CAN communication circuit: measure voltage to ground at G36-15 (CAN-H) and G36-14 (CAN-L) (normally approx. 2.5V) and terminal resistance (approx. 60Ω) to rule out wiring shorts or open circuits.
  • 5
    Perform the SRS ECU pre-removal safety procedure: disconnect the negative battery terminal, wait at least 3 minutes for the capacitors to discharge, and inspect the ECU exterior for physical damage, water stains, or burn marks.
  • 6
    Replace the SRS ECU assembly with the same part number (Note: On some models, the ECU, steering wheel clock spring, and airbag are a matched set; confirm the configuration).
  • 7
    Use the diagnostic tool to program and configure the new ECU: write the vehicle VIN, model configuration code, airbag deployment parameters, and seat belt pretensioner configuration.
  • 8
    Perform system self-check and calibration: Use the diagnostic tool to perform 'Crash Sensor Zero Point Calibration' and 'System Self-check', and confirm the system generates no new fault codes.
  • 9
    Clear the history fault codes, cycle the ignition switch from OFF to ON 3 times, and confirm the instrument cluster SRS warning light performs a normal self-check (illuminates for 5 seconds, then turns off).
  • 10
    Perform passive safety system functional verification: Use the diagnostic tool to perform a 'collision simulation test' (without deploying the actual airbags), verify normal ECU communication and sensor response, and finally perform a road test.
Real-World Cases
BYD DTC AI Analysis

BYD Qin Pro SRS ECU Internal Fault Replacement Case

✓
The SRS fault light on the instrument cluster stayed on. The diagnostic scanner read fault code B1699-00 (airbag electronic control unit fault). The technician first checked G36 connector pin 35 constant battery voltage: 12.4V, normal. Pin 34 IG1 voltage normal. Earth resistance: 0.3Ω, normal. This ruled out external circuit issues. CAN bus voltage was normal, no shorts or open circuits. The technician diagnosed an internal ECU processor fault. After replacing with a new SRS ECU, the technician used the VDS scanner to perform 'Write VIN' and 'System Configuration', then cleared the fault codes. The SRS light went out normally and the system self-test passed.
Original source ↗
BYD DTC AI Analysis

BYD Song DM SRS communication fault with B1699

✓
The SRS warning light illuminated intermittently while driving. The scan tool occasionally retrieved DTC B1699 and communication timeout faults. Further inspection revealed a backed-out pin at the G09-14/15 harness connector, causing intermittent CAN communication interruption. The ECU internal communication fault counter overflowed, triggering B1699. After repairing the backed-out pin and re-crimping the terminal, communication returned to normal. This case shows: even if the fault code points to an internal ECU fault, always check the reliability of external harness connections, especially on accident-repaired vehicles.
Original source ↗
BYD DTC AI Analysis

BYD Yuan EV SRS ECU failure after water wading

✓
After driving through water, the instrument cluster displayed an SRS fault. Inspection found the SRS ECU beneath the centre console had water ingress during wading, corroding the internal circuit board. Disassembling the ECU revealed verdigris on the main control chip pins and internal EEPROM data verification failure, setting non-clearable DTC B1699-00. Replaced the ECU, cleaned the water residue off the wiring harness connectors, programmed the new module, and calibrated the impact sensors. System returned to normal. Recommend checking the SRS ECU sealing and for water pooling at the mounting location on any vehicle that has waded through water.
Original source ↗
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.