AU
B1773-00

DTC B1773-00 indicates the airbag control unit (SRS ECU) failed to detect the electrical signal or communication response from the right rear seat belt pretensioner during the system self-check — Qin Plus

Safety System

DTC B1773-00 indicates the airbag control unit (SRS ECU) failed to detect the electrical signal or communication response from the right rear seat belt pretensioner during the system self-check.

This passive safety system hardwire/communication fault indicates an abnormality in the squib circuit between the SRS module and the right rear seat belt pretensioner.

Causes include an open circuit, a short to ground or power, or the pretensioner internal igniter resistance falling outside the standard range (typically 1.5-3.5Ω).

This fault prevents the pretensioner from deploying and tightening the seat belt during a collision, significantly reducing occupant protection.

The SRS system also enters fail-safe mode, which may disable other airbags and illuminate the airbag warning light continuously.

The B1773-00 fault code on the Qin Plus indicates the SRS ECU cannot detect a proper signal from the right rear seat belt pretensioner. This is a medium-severity safety fault because the pretensioner may not deploy in a crash. Common causes include a loose or damaged yellow pretensioner connector or abnormal igniter resistance. Visit an authorised dealer for SRS diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1The right rear seat belt pretensioner connector (usually a yellow waterproof plug) is loose, disconnected, or has poor contact. Common causes include frequent forward and backward seat movement, incomplete insertion after removal, or a broken locking tab.
  • 2Open circuit or abnormal resistance in the pretensioner internal igniter (aging, moisture ingress, previous deployment, or manufacturing defect), preventing the SRS module from detecting the standard resistance circuit.
  • 3Physical damage to the wiring harness causing open or short circuits, especially pinched wires under the seat rails, wear points at bends inside the B-pillar trim panel, or fatigue fractures at the door hinge wiring pass-through.
  • 4High resistance, intermittent open circuit, or oxidized connector pins in the communication circuit between the SRS control module and the pretensioner (especially in high-humidity areas or after driving through water).
  • 5Pretensioner deployed during a vehicle accident but remains unreplaced, or an installed non-genuine part causes a resistance mismatch, triggering the system to identify it as 'not present'.
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal and wait at least 90 seconds to ensure the SRS capacitor discharges fully to prevent accidental airbag deployment. Wear an anti-static wrist strap and prepare the BYD dedicated diagnostic tool (VDS2000/ED400).
  • 2
    Fault confirmation: Connect the diagnostic tool to read the DTCs. Confirm B1773-00 is a current (Active) fault, not a historical fault, and record the freeze frame data. Check for accompanying communication fault codes (such as B1772, B1774).
  • 3
    Connector inspection: Remove the right rear seat and lower B-pillar trim panel. Verify the yellow pretensioner connector is secure. Confirm the locking tab (CPA) fully seats. Inspect the connector interior for moisture, oxidation, or backed-out pins.
  • 4
    Resistance measurement: Disconnect the pretensioner connector. Use a multimeter to measure the resistance between the pretensioner terminals. Normal resistance is 1.5-3.5 Ω (refer to the specific model repair manual). Infinity indicates an internal open circuit, and 0 Ω indicates an internal short circuit. Replace the assembly if either condition exists.
  • 5
    Harness continuity test: Measure the harness resistance between the SRS module and pretensioner ends; it must be less than 1 Ω. Measure the harness insulation resistance to ground and power; it must be infinite. Carefully inspect seat rail pinch points and body pass-through holes.
  • 6
    Component Replacement and Verification: If the pretensioner is faulty, replace the right rear seat belt assembly (includes the pretensioner; do not replace the igniter separately). If the wiring harness is faulty, repair the wiring harness. After reassembly, clear the fault code and perform an SRS system self-check (turn the ignition switch ON and verify the warning lamp turns off after 6 seconds). If necessary, execute the diagnostic tool's 'Crash Output Test' function to verify circuit integrity.
Real-World Cases
BYD DTC AI Analysis

Intermittent fault caused by pretensioner connector not locked after seat removal

✓
2018 BYD Qin EV450, airbag warning light illuminates intermittently. VDS read DTC B1773-00 (intermittent). Owner reported removing the seats for deep cleaning at a detailing shop one week prior. Inspection found the yellow connector for the right rear seatbelt pretensioner inserted but the CPA (Connector Position Assurance) lock tab not fully seated; vehicle vibration caused poor contact. Reseated the connector and confirmed the CPA lock engaged. Cleared the DTC and monitored for one week with no recurrence.
BYD DTC AI Analysis

Seat rails crushed wiring harness causing intermittent open circuit

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2017 BYD Qin 80. Airbag warning light illuminated randomly while driving. Scanner showed B1773-00 as a current/history alternating fault. Pretensioner resistance measured normal at rest, but the reading fluctuated when manually sliding the seat fore and aft. Disassembly revealed the wiring harness insulation had been cut by the seat rail edge at the mounting point, with copper conductors partially fractured leaving only a few strands intact. Resoldered the harness and fitted abrasion-resistant corrugated tubing, repositioned the retaining clip to prevent contact with moving components. Fault permanently resolved.
BYD DTC AI Analysis

Water ingress caused internal short circuit in pretensioner, triggering fault code

✓
A Qin 100 drove through floodwater after heavy rain (water depth exceeded the door sills). The airbag warning light stayed on. Pulled DTC B1773-00. Measured pretensioner resistance at 0.2Ω—well below spec, confirming an internal short. Disassembly revealed the pretensioner housing seal had degraded, allowing water to enter; the internal igniter got wet and the insulation between electrodes failed. Replaced the right rear seatbelt assembly (includes pretensioner). Removed rust from the wiring harness connectors, dried them, and applied conductive grease and waterproof sealant. Cleared the fault codes; system self-check passed.
BYD DTC AI Analysis

Oxidized SRS module pins caused high resistance fault

✓
A 5-year-old Qin EV300 developed DTC B1773-00. Pretensioner resistance measured 2.1Ω (normal); harness continuity checked good. Further inspection of the SRS control module connector showed green corrosion on the right rear pretensioner pins, with contact resistance at 12Ω (out of spec). Cleaned the pins with electronic contact cleaner and a non-metallic brush, lightly sanded to restore the metallic shine, then applied specialized conductive grease. Fault code cleared; pretensioner circuit resistance returned to normal range.
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.