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 — Qin Plus

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 Qin Plus indicates a medium-severity open circuit in the second-stage firing circuit of the driver-side front airbag. This can reduce or disable staged airbag deployment in a crash. Common causes include a damaged clock spring or poor connector contact, or an open second-stage airbag igniter. The recommended fix is to visit an authorised dealer for SRS diagnosis and repair. Typical repair cost data is available from recorded cases.
3
Cases Logged
5
Causes
Likely Causes — Qin Plus
  • 1Internal open circuit or poor contact in the clock spring (spiral cable), especially internal flat ribbon cable breakage caused by prolonged steering.
  • 2Driver airbag module second-stage igniter internal open circuit or resistance out of specification (standard value: 1.5-3.0 Ω)
  • 3Loose, oxidized, or water-damaged yellow airbag wiring harness connector under the steering wheel (usually a 2-pin yellow plug), or terminal back-out.
  • 4Open circuit, corrosion, or deformed pins at the floor wiring harness to steering column wiring harness connector; common in vehicles driven through water or with damp floors.
  • 5SRS control unit internal diagnostic circuit fault (less common; rule out wiring faults before confirming)
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 (allowing the SRS backup power capacitor to fully discharge). Never use a multimeter in resistance mode to directly measure the airbag module.
  • 2
    Initial visual inspection: Verify the yellow airbag connector below the steering wheel is fully locked. Inspect the wiring harness for abrasion, crushing, or rodent damage. Check the clock spring housing for damage.
  • 3
    Sectional 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 (specified value: 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 the continuity of its internal second-stage circuit. If resistance is infinite or unstable, replace the clock spring (part number usually marked 'Clock Spring' or 'spiral cable').
  • 5
    Harness repair: If the connector is loose, reconnect and secure the retaining clip; if a terminal is oxidized or a pin has backed out, repair using a dedicated terminal removal tool or replace the wiring harness assembly; check the mating connector between the floor harness and the steering column harness (usually located behind the trim panel below the steering wheel).
  • 6
    System Reset and Verification: After repair, reconnect all components and the battery. 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 light 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 Qin Plus 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.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 Qin Plus →Qin Plus 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.