AU
B1691-00

B1691-00 (Factory Encrypted) is a safety configuration fault code for the BYD SRS (Supplemental Restraint System) — Atto 8

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 8 indicates a medium severity airbag computer error where corrupted encrypted safety data disables deployment to prevent accidental firing. This typically occurs after improper replacement without configuration or power loss causing memory corruption. Repair requires a BYD diagnostic tool at an authorised dealer. Typical repair cost data is available from 3 recorded cases.
3
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Failed 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 servicing causes the ECU's internal volatile memory to lose encrypted configuration data.
  • 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) making encrypted chip data unreadable.
What To Do
  • 1
    Basic circuit check: Measure the battery voltage (must be ≥12V). Verify normal voltage at power supply pins (B+, IG1) of 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, access the SRS system, and read and record all fault codes. Verify B1691-00 is present. Check history faults and freeze frame data to confirm 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: Enter 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, 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. 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 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.