AU
B1691-00

B1691-00 (Factory Encrypted) is a safety configuration fault code for the BYD SRS (Supplemental Restraint System) — Atto 3

Safety System

B1691-00 (Factory Encrypted) is a safety configuration fault code for the BYD SRS (Supplemental Restraint System).

It indicates an error in the unique encrypted configuration data stored within the airbag ECU (Electronic Control Unit) and bound to the vehicle VIN.

This fault indicates the ECU detected missing, corrupted, or mismatched internal safety configuration data, triggering the system safety lock mechanism.

In this state, the airbag system disables deployment to prevent accidental deployment or failure caused by an unauthorized ECU, incorrect configuration, or data corruption.

This condition severely compromises the vehicle's passive safety performance.

Reconfigure the system using the manufacturer's dedicated diagnostic equipment.

The B1691-00 fault code on the Atto 3 indicates a safety configuration error in the airbag system where encrypted data in the ECU is missing, corrupted, or mismatched, causing the system to lock and disable deployment. This medium severity issue typically occurs after improper ECU replacement without configuration or power loss during maintenance. Visit an authorised dealer to reconfigure the system using dedicated diagnostic equipment. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1Failure to perform the 'ECU Configuration' or 'Factory Mode' encrypted write operation using the BYD dedicated diagnostic tool (VDS/ED-400) after replacing the airbag ECU.
  • 2Severe vehicle battery discharge, prolonged power disconnection, or power interruption during maintenance caused the loss of encrypted configuration data in the ECU internal volatile memory.
  • 3After a vehicle collision, the SRS system triggers lockout protection and the ECU enters the 'deployed' or 'requires reconfiguration' state.
  • 4Incorrect ECU programming, flashing, or data erasure during unauthorized repairs corrupted the factory-encrypted data.
  • 5Incomplete end-of-line configuration, or ECU hardware fault (such as internal EEPROM/Flash damage) preventing the reading of encrypted chip data.
What To Do
  • 1
    Basic circuit check: Measure battery voltage (must be ≥12V). Verify normal voltage at power supply pins (B+, IG1) on SRS ECU connector G36. Measure resistance between ground pin G36-35 and body ground (should be <1Ω) to rule out wiring faults.
  • 2
    Fault confirmation and recording: Connect the BYD dedicated diagnostic tool, enter the SRS system, and read and record all fault codes. Confirm B1691-00 is present. Check historical faults and freeze frame data to verify no other accompanying hardware fault codes exist.
  • 3
    ECU status check: Use the diagnostic tool to read the ECU identification information (VIN, part number, software version), verify the read VIN matches the actual vehicle VIN, and check the configuration data integrity flag.
  • 4
    Perform factory configuration: Go to the diagnostic tool's 'Special Functions' or 'ECU Configuration' menu, select 'SRS System Configuration' or 'Factory Encrypted Write', enter the correct vehicle VIN, model configuration code (if applicable), and calibration data, and execute the encrypted data write and matching operation.
  • 5
    Verification and testing: After completing the configuration, use the diagnostic tool to clear all stored fault codes. Cycle the power mode from OFF → ON (wait 20 seconds) → OFF. Read the fault codes again to confirm B1691-00 does not reappear. Verify the instrument panel SRS warning light turns off normally. Perform the SRS system self-check function to confirm no abnormalities.
Real-World Cases
BYD DTC AI Analysis

BYD Qin EV sets DTC B1691-00 after airbag ECU replacement.

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A 2018 Qin EV450 had its airbag ECU assembly replaced with a new unit at a dealership following a front-end collision. After installation, the SRS warning light stayed on. Using a VDS diagnostic tool, the technician retrieved fault code B1691-00 (factory encryption). The technician first measured power supply and earth at the G36 connector and found both normal, concluding the new ECU had not completed initial configuration. Using the diagnostic tool, the technician accessed the SRS system special functions, performed the 'ECU factory configuration' procedure, entered the vehicle VIN and model configuration parameters, and completed the encrypted data write. After configuration, the technician cleared the fault code and cycled the ignition for the self-check. The SRS light went out and the fault was resolved.
Original source ↗
BYD DTC AI Analysis

Extended power loss caused SRS encrypted data loss in the Qin 100.

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A 2017 Qin 100 sat for an extended repair, its negative battery terminal disconnected for over 48 hours. After reconnecting, the cluster showed an SRS fault. A scan revealed DTC B1691-00. Checks of the ECU power supply and ground circuits found nothing wrong. The extended power loss had caused the ECU to lose its stored encrypted factory configuration. A technician used a dedicated diagnostic tool to run the 'SRS System Restore Factory Configuration' function, rewrote the encrypted data, and completed system calibration. After clearing the DTC, the SRS self-test returned to normal and the warning light went out.
Original source ↗
BYD DTC AI Analysis

Used ECU VIN mismatch triggers factory encryption fault.

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A Qin 80 had a second-hand airbag ECU from another vehicle installed at a non-authorised repair shop. After installation, the SRS warning light illuminated on the instrument panel. Fault code retrieval returned DTC B1691-00. Reading the ECU information with a diagnostic tool showed the stored VIN did not match the vehicle's original VIN, triggering the factory encryption protection mechanism. Since simple configuration cannot change the VIN binding on a second-hand ECU, the solution was to replace it with a brand-new genuine airbag ECU and use the VDS diagnostic tool to perform the correct 'new component configuration' procedure, entering the original VIN to complete the encryption match and clear the fault.
Original source ↗
Other Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.
Common problems reported for Atto 3 →Atto 3 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.