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 — Seal 6 EV

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 Seal 6 EV indicates the SRS ECU cannot detect the right rear seat belt pretensioner during its self-check. This is a medium-severity safety fault because the pretensioner may not work in a crash. Common causes include a loose yellow pretensioner connector or an open/abnormal resistance in the pretensioner squib. Visit an authorised dealer for 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 — Seal 6 EV
  • 1Right 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, failure to fully insert the connector after removal, or a broken locking tab.
  • 2Open circuit or abnormal resistance in the pretensioner internal squib (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 an open or short circuit, especially wiring pinched under the seat rail, 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 connector pin oxidation in the communication circuit between the SRS control module and the pretensioner (especially in high-humidity areas or after wading).
  • 5Pretensioner deployed during a vehicle accident but not replaced, or installation of a non-genuine part causes a resistance mismatch, triggering the system to identify the component as 'not present'.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds to fully discharge the SRS capacitor and 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 DTCs. Confirm B1773-00 is a current fault (Active) and not a history fault, and record the freeze frame data. Check for accompanying communication fault codes (such as B1772, B1774).
  • 3
    Connector check: Remove the right rear seat and lower B-pillar trim panel. Check the yellow pretensioner connector for a secure connection. Confirm the locking tab (CPA) fully engages. Inspect the connector plug for moisture, oxidation, or backed-out terminals.
  • 4
    Resistance measurement: Disconnect the pretensioner connector. Use a multimeter to measure the resistance between the pretensioner terminals. The normal value is 1.5-3.5 Ω (refer to the specific vehicle repair manual). Infinite resistance indicates an internal open circuit, and 0 Ω indicates an internal short circuit. Replace the assembly in either case.
  • 5
    Harness continuity test: Measure the harness resistance between the SRS module end and the pretensioner end; resistance must be less than 1 Ω. Measure the harness insulation resistance to ground and power supply; resistance must be infinite. Focus inspection on seat rail pinch points and body pass-through holes.
  • 6
    Component replacement and verification: If confirming a pretensioner fault, replace the right rear seat belt assembly (includes the pretensioner; do not replace the igniter separately). If confirming a wiring harness fault, repair the 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

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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

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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 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.