AU
B1691

DTC B1691 indicates the Airbag Control Module (ACM) detects a verification failure of its internally stored factory-encrypted data or security authentication key — Atto 3

Safety System

DTC B1691 indicates the Airbag Control Module (ACM) detects a verification failure of its internally stored factory-encrypted data or security authentication key.

This fault involves the SRS security authentication mechanism.

The module triggers this fault when its stored factory configuration data, encryption key, or anti-theft authentication information does not match the reference data stored in the VCU/BCM.

Common causes include: installing a non-genuine airbag module without online matching, corrupted internal EEPROM data, vehicle power system anomalies causing encrypted data loss, or failing to complete the module matching procedure correctly during production or repair.

This safety-related fault causes the airbag system to enter a degraded mode and may limit normal airbag deployment.

3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Replacing the airbag control module (ACM) with a non-genuine part or failing to perform online matching causes an encryption key mismatch with the vehicle.
  • 2Electromagnetic interference, static electricity, or hardware failure corrupted the factory configuration data or encryption key stored in the airbag module.
  • 3Severe vehicle battery discharge, improper jump-starting, or power supply system voltage fluctuations causing module data loss.
  • 4Operating the SRS system with non-dedicated diagnostic equipment during repairs, accidentally triggering factory mode or overwriting encrypted data.
  • 5Software upgrade failure or module hardware fault (such as EEPROM damage) causes security authentication algorithm verification failure.
What To Do
  • 1
    Use the BYD VDS diagnostic tool to read the complete fault codes and freeze frame data, verify if B1691 is a current fault, and record the vehicle status at the time of the fault.
  • 2
    Check the airbag control module (ACM) power supply (constant B+, ignition IG1), ground, and CAN-H/CAN-L circuit connections. Verify the supply voltage is 12V ± 0.5V and the ground resistance is less than 1Ω.
  • 3
    Perform the 'SRS System Online Matching' or 'Factory Encrypted Reset' procedure. Verify and rewrite the module encryption data via the BYD official server to ensure the module matches the vehicle VIN and anti-theft system.
  • 4
    If online matching fails, verify the module part number, hardware version, and software version match the vehicle configuration. If necessary, replace with a new genuine ACM and repeat the matching procedure.
  • 5
    After completing the matching, clear the fault code and perform the 'SRS system self-check'. Verify the airbag warning light turns off normally. Perform a battery disconnect test and a road test to ensure the fault does not recur.
Real-World Cases
BYD DTC AI Analysis

Replaced SRS module with salvaged unit on accident-damaged vehicle, now showing B1691.

✓
After a front-end collision, a workshop installed a used airbag control module (ACM) from the same model into a 2021 BYD Tang. The airbag warning light remained on. VDS diagnosis retrieved DTC B1691 (Factory Encryption), which would not clear. Inspection revealed the salvaged module had not been unbound. The workshop then fitted a new genuine ACM, performed online matching and immobiliser authentication via VDS, cleared the DTC, and restored normal airbag system function.
BYD DTC AI Analysis

Extended stationary period caused battery discharge, resulting in abnormal SRS data

✓
A 2019 BYD Yuan EV sat for about 3 months, causing severe battery discharge (voltage below 5V). After jump-starting, the instrument cluster displayed "Check SRS System". The scanner retrieved DTC B1691 and low-voltage history records. Charged the battery, replaced the aging battery, and used VDS to perform "SRS System Initialization" and "Clear History Faults". The DTC cleared. Low voltage caused a temporary module data anomaly.
BYD DTC AI Analysis

Software upgrade interrupted, causing encryption verification failure

✓
A 2020 BYD Qin SRS control module software update failed when the diagnostic tool lost connection mid-process. After reconnecting, the instrument cluster displayed the airbag warning light and stored DTC B1691. Reflashing the software had no effect. Using the VDS, the technician executed the 'Factory Encryption Reset' special function and then re-performed the module-to-vehicle identity authentication and data synchronisation, which cleared the fault.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.