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B1691-00

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

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.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Failure to use the BYD dedicated diagnostic tool (VDS/ED-400) to perform the 'ECU Configuration' or 'Factory Mode' encrypted write operation 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 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) causing unreadable encrypted chip data.
What To Do
  • 1
    Basic circuit check: Measure the battery voltage (must be ≥12V). Verify normal voltage at power supply pins (B+, IG1) on SRS ECU connector G36. Measure the 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. Verify B1691-00 is present. Check history faults and freeze frame data, and verify no other accompanying hardware fault codes exist.
  • 3
    ECU status check: Use the diagnostic tool to read ECU identification information (VIN, part number, software version), verify it matches the actual vehicle VIN, and check the configuration data integrity flag.
  • 4
    Perform factory configuration: Access the diagnostic tool '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, then 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, then read the fault codes again to confirm B1691-00 no longer appears. Verify the instrument panel SRS warning light turns off normally and 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.

✓
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 Seal U 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.