AU
B1787-00

DTC B1787-00 indicates the SRS (Supplemental Restraint System) control module detects an open circuit fault (abnormal resistance or open circuit) in the second-stage firing circuit of the driver-side dual-stage front airbag — Seal 6 EV

Safety System

DTC B1787-00 indicates the SRS (Supplemental Restraint System) control module detects an open circuit fault (abnormal resistance or open circuit) in the second-stage firing circuit of the driver-side dual-stage front airbag.

Modern BYD models use a dual-stage airbag design; the first and second stages correspond to different deployment strategies based on collision severity.

A "not connected" system report indicates the ECU cannot establish a complete circuit path to the second-stage inflator.

This prevents the airbag from executing its staged deployment strategy during a moderate to severe collision, potentially triggering only the first stage or failing completely.

The SRS also illuminates the instrument cluster airbag warning light and may disable the entire driver-side front airbag function, severely compromising crash protection performance.

The B1787-00 fault code on the Seal 6 EV indicates an open circuit in the second-stage firing circuit of the driver-side dual-stage front airbag. Severity is medium, as it can reduce or disable proper airbag deployment in a crash. Common causes include a faulty clock spring/spiral cable or an open-circuit second-stage airbag igniter. The recommended fix is to visit an authorised dealer for SRS diagnosis and repair. Typical repair cost data is available.
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Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Open circuit or poor contact inside the clock spring (spiral cable), especially internal flat ribbon cable breakage due to prolonged steering.
  • 2Driver airbag module stage 2 igniter internal open circuit or resistance out of specification (standard value: 1.5-3.0 Ω)
  • 3Loose connection, oxidation, or water ingress at the yellow airbag wiring harness connector below the steering wheel (usually a 2-pin yellow plug), or terminal back-out.
  • 4Open circuit, corrosion, or deformed pins at the connector between the floor wiring harness and steering column wiring harness, common in vehicles with water ingress or damp floors.
  • 5SRS control unit internal diagnostic circuit fault (less common; confirm after ruling out wiring faults)
What To Do
  • 1
    Safe power-down: Turn off the ignition switch, disconnect the 12V low-voltage battery negative terminal, and wait at least 90 seconds (to ensure the SRS backup power capacitor discharges completely). Never measure the airbag assembly directly using a multimeter resistance setting.
  • 2
    Initial visual inspection: Verify the yellow airbag connector below the steering wheel is fully locked, inspect the wiring harness for wear, pinching, or rodent damage, and check the clock spring housing for damage.
  • 3
    Segmented resistance measurement: Remove the driver airbag (wait at least 90 seconds after disconnecting the battery). Use a digital multimeter to measure the resistance between the second-stage terminals of the airbag unit (should be 1.5-3.0 Ω). If normal, measure the continuity of the wiring harness from the vehicle side of the clock spring to the SRS ECU.
  • 4
    Clock spring inspection: Disconnect the connectors at both ends of the clock spring and measure continuity of the internal second-stage circuit. If resistance is infinite or unstable, replace the clock spring (part numbers usually indicate 'Clock Spring' or 'spiral cable').
  • 5
    Wiring harness repair: If the connector is loose, reconnect it and secure the locking clip; if a terminal is oxidized or a pin has backed out, repair it using a dedicated terminal release tool or replace the wiring harness assembly; check the mating connector between the floor wiring harness and the steering column wiring harness (usually located behind the trim panel below the steering wheel).
  • 6
    System reset and verification: After repair, reconnect all components and restore the battery connection. Use the diagnostic tool to clear the fault code. Perform the 'SRS system self-check' or 'configuration and calibration' procedure. Confirm B1787-00 does not return and the airbag warning lamp turns off.
Real-World Cases
BYD DTC AI Analysis

BYD Qin EV300 Clock Spring Open Circuit Causing DTC B1787-00

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Vehicle: 2017 BYD Qin EV300. Symptom: Airbag warning light on steady. Retrieved current DTC B1787-00 using VDS2000. Diagnostic procedure: Technician disconnected the battery negative terminal, waited 90 seconds, and removed the driver airbag module. Measured the airbag second-stage circuit resistance at 2.1Ω (normal). Further testing of the clock spring body-side harness revealed an open circuit in the second stage. Disassembled the clock spring and found the internal flat ribbon cable broken at the steering wheel. Solution: Replaced the driver-side clock spring assembly (part number: B2J-58200XX). After reassembly and clearing the fault codes, the airbag warning light went out and the fault cleared.
BYD DTC AI Analysis

Qin Pro: Loose connector under steering wheel causing intermittent warning

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Vehicle: BYD Qin Pro DM. Symptoms: SRS warning light intermittent; frequent on rough roads. Diagnostics: Retrieved historic DTC B1787-00. Diagnosis: Yellow 2-pin airbag connector under steering wheel had not fully latched; harness pulled loose with gentle tug. No terminal oxidation, but contact surfaces showed slight burn marks. Repair: Cleaned terminals with electronic contact cleaner. Reconnected until latch clicked. Secured harness with cable ties. Cleared DTCs. Monitored one week with no recurrence.
BYD DTC AI Analysis

Water damage corroded the floor wiring harness, causing an open circuit in the airbag circuit.

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Vehicle: BYD Qin 100. Symptoms: Airbag warning light stayed on after flood damage repairs, storing DTC B1787-00. Diagnosis: Airbag and clock spring both tested normal. Traced the wiring harness and found the floor harness-to-steering column harness connector (under the driver-side dashboard) had standing water and green corrosion inside. The second stage circuit pin (typically the specific pin in the yellow wire) had corroded and broken. Repair: Cut out the corroded connector and soldered the harness to fix the break. Sealed the repair with waterproof insulation. Replaced the floor harness section if necessary. Cleared the fault code after repair; system returned to normal.
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.