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 — Seal 6 EV

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.

The B1691 fault code on the Seal 6 EV indicates the airbag control module has detected a verification failure of its factory-encrypted data or security key, causing the system to enter a degraded mode. This medium severity issue typically occurs when a non-genuine module is installed without proper online matching, or when internal data becomes corrupted. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available based on 3 recorded cases.
3
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Installing a non-genuine Airbag Control Module (ACM) or failing to match the module online, causing an encryption key mismatch with the vehicle.
  • 2Electromagnetic interference, static electricity, or a hardware fault 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 update failure or module hardware fault (such as damaged EEPROM) causes security authentication algorithm verification failure.
What To Do
  • 1
    Use the BYD VDS diagnostic tool to read all fault codes and freeze frame data. Confirm 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. Measure the supply voltage to verify it is within 12V±0.5V, and confirm 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 official BYD server to match the module with 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 matching, clear the fault code and perform the 'SRS system self-check'. Confirm the airbag warning light turns off normally. Perform a battery disconnect test and a road test to verify 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 Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.