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B1699-00

B1699-00 indicates an internal hardware or basic software fault in the airbag electronic control unit (SRS ECU) — Qin Plus

Safety System

B1699-00 indicates an internal hardware or basic software fault in the airbag electronic control unit (SRS ECU).

This ECU integrates a central acceleration sensor, a crash detection algorithm processor, ignition driver circuits, and an energy storage capacitor.

The following conditions trigger the DTC: abnormal ECU supply voltage (below 9V or above 16V for longer than the set time), internal memory (EEPROM/Flash) checksum failure, main control chip (MCU) watchdog reset, acceleration sensor self-test failure, or CAN communication controller fault.

This is a hard fault.

The ECU enters fail-safe mode and disables all airbag ignition circuits, preventing the airbags and seat belt pretensioners from deploying during a collision and posing a severe safety hazard.

4
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1SRS ECU internal hardware damage (voltage regulator chip breakdown, main control MCU cold solder joint, acceleration sensor module failure)
  • 2Power supply system fault (discharged battery, blown fuse SB09, burnt ignition switch contacts causing unstable voltage)
  • 3Ground circuit fault (loose or oxidized G36 connector or broken ground wiring harness causing contact resistance greater than 1Ω)
  • 4CAN network communication fault (CAN-H and CAN-L shorted together, short to power or ground, terminal resistor drift)
  • 5Software/calibration data corrupted (interrupted flashing or strong electromagnetic interference causing loss of collision threshold calibration data)
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 3 minutes to allow the SRS ECU energy storage capacitor to fully discharge to prevent accidental airbag deployment.
  • 2
    Visual inspection: Check the SRS ECU housing located under the dashboard or center console for physical damage, burn marks, or liquid ingress.
  • 3
    Power supply check: Connect the battery, turn the ignition ON, and measure the voltage at ECU connector pin 16 (B+ constant power) and pin 1 (IG power). Standard range: 9-16V. The waveform must be stable without pulsation.
  • 4
    Ground verification: Measure the resistance between ECU connector pin 15 and body ground point G36. The resistance must be less than 1 Ω. Verify the connector latch is intact and no terminals have backed out.
  • 5
    Communication test: Use an oscilloscope to check CAN-H (2.5-3.5V) and CAN-L (1.5-2.5V) waveforms. Measure terminating resistance (approximately 60Ω) and confirm no short or open circuits.
  • 6
    Harness continuity: Disconnect the ECU connector. Measure harness continuity to the left/right crash sensors and the instrument cluster. Measure insulation resistance to ground (must be greater than 1MΩ).
  • 7
    Replacement verification: Install a known-good SRS ECU with the same part number (observe anti-static precautions) and check if the fault code transfers.
  • 8
    Online programming: After replacing the ECU, use VDS2000/ED400 to perform online programming, write the VIN, and set the configuration word (manufacturer authorization required).
  • 9
    Sensor calibration: Perform zero-point calibration of the lateral and longitudinal acceleration sensors, and check the seat belt pretensioner resistance (standard value: 2.0-3.0Ω).
  • 10
    Final verification: Clear the fault code, perform 3 ignition cycle self-checks, use the diagnostic tool to read the historical data stream to confirm no abnormalities, and road test the vehicle to confirm the airbag warning light turns off normally.
Real-World Cases
BYD DTC AI Analysis

Qin EV300 SRS ECU internal chip overheated and damaged

✓
While driving, the airbag warning light suddenly came on and stayed on. VDS retrieved DTC B1699-00, which could not be cleared. Measured ECU supply voltage: 12.4 V (normal). G36 ground resistance: 0.3 Ω (normal). CAN communication waveform showed no abnormalities. Disassembled the ECU and found discolouration from overheating on the internal voltage regulator (LDO), indicating an internal short circuit that caused the ECU self-test to fail. Replaced with a new SRS ECU (part number: ...), performed online programming and sensor calibration, and resolved the fault.
Original source ↗
BYD DTC AI Analysis

Qin EV450 ECU data corrupted due to prolonged battery depletion

✓
The battery went flat (8.5V) after the vehicle sat unused for an extended period. Following a jump-start, the airbag warning light came on with DTC B1699-00 logged. Fitted a new battery and restored normal voltage, but after clearing the codes and driving the light returned. Further inspection found the ECU's internal flash memory experienced a checksum error during the low-voltage condition. Replaced the SRS ECU and upgraded the software to resolve the fault. The owner was advised to avoid parking the vehicle for long periods with a discharged battery.
BYD DTC AI Analysis

BYD Qin 100 ground terminal corrosion after wading through water

✓
After the vehicle was driven through water, the airbag warning light came on and a diagnostic scan showed DTC B1699-00. Inspection found water traces at the ECU mounting location (beneath the dashboard) and severe internal corrosion in the G36 ground connector. We measured the ground resistance at 12 Ω (spec: <1 Ω). We cleaned the connector terminals, applied conductive grease, and retightened the ground nut. The DTC became intermittent. Finally, we replaced the SRS ECU assembly to completely clear the fault.
BYD DTC AI Analysis

Aftermarket OBD device installation in a Qin 80 caused CAN bus interference.

✓
After the owner fitted a third-party OBD smart box, the airbag warning light illuminated intermittently and DTC B1699-00 appeared sporadically. Inspection found that the aftermarket device drew power from the OBD port and was wired in parallel to the CAN bus, intermittently interrupting communication between the SRS ECU and instrument cluster. The ECU misinterpreted this as an internal communication fault. Removing the modified wiring and restoring the factory OBD harness fixed the issue—the fault code never reappeared. Avoid connecting non-genuine devices in parallel on the CAN bus circuits used by the airbag system.
Other Qin Plus 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.