AU
B1699

DTC B1699 indicates an internal self-check fault in the airbag system Electronic Control Unit (SRS ECU) — Atto 8

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 8
  • 1Hardware damage to the main control chip, memory, or ignition drive circuit inside the SRS ECU, typically occurring in older vehicles or vehicles exposed to strong electromagnetic interference.
  • 2Abnormal ECU power supply voltage (battery voltage continuously exceeding 16V or dropping below 9V) causes internal power management module breakdown or protection circuit lock-up.
  • 3During a previous collision, the ECU internal acceleration sensor detected an impact but the airbag did not deploy, causing internal diagnostic circuit lock-up or physical sensor damage.
  • 4Extreme environmental conditions (high temperature and humidity, wading) cause internal ECU circuit board corrosion, dry solder joints, or bulging capacitors, affecting signal processing accuracy.
  • 5Corrupted software data or an interrupted flashing process causes ECU firmware verification failure, preventing normal completion of the initialization self-check.
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 between connector G36 pin 35 (constant power +B) and ground; it should be battery voltage. The voltage at pin 34 (IG1 power) should be 12V with the ignition ON. Check fuse F4/9 and related relays.
  • 3
    Check the ECU ground circuit: measure the resistance between G36-35 and body ground. The resistance must be less than 1 Ω. Inspect ground point G109 for oxidation or looseness.
  • 4
    Check the CAN communication lines: Measure voltage to ground at G36-15 (CAN-H) and G36-14 (CAN-L) (normally about 2.5V) and terminal resistance (about 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 capacitor to discharge, and inspect the ECU exterior for physical damage, water stains, or burn marks.
  • 6
    Replace the SRS ECU assembly with one of the same part number (Note: On some models, the ECU, steering wheel clock spring, and airbag are matched components; verify 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 stored 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 function verification: Use the diagnostic tool to perform a 'collision simulation test' (without triggering actual airbags). Verify normal ECU communication and sensor response. Finally, perform a road test to verify.
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 8 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.