AU
B1772

DTC B1772 indicates the right rear seatbelt pretensioner ignition circuit resistance exceeds the standard upper limit (typically >3 — Qin Plus

Safety System

DTC B1772 indicates the right rear seatbelt pretensioner ignition circuit resistance exceeds the standard upper limit (typically >3.6Ω or open circuit).

The seatbelt pretensioner is a key SRS (Supplemental Restraint System) actuator containing an internal squib.

During a collision, the SRS control unit (ACU) sends current to the squib to ignite the propellant, instantly tightening the seatbelt to protect the occupant.

Excessive resistance indicates high resistance, poor contact, or a complete open circuit in the ignition circuit, preventing the ACU from activating the pretensioner.

During a collision, the rear occupant on that side loses pretensioner protection, significantly increasing safety risks.

Typical causes include connector oxidation, wiring harness damage, or internal pretensioner squib failure.

The B1772 fault code on the Qin Plus indicates excessive resistance or an open circuit in the right rear seatbelt pretensioner ignition circuit. Severity is medium because the pretensioner may not work in a crash, reducing occupant protection. Common causes include a loose or oxidized connector, damaged wiring, or an internal pretensioner igniter fault. 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
  • 1Loose right rear seat belt pretensioner connector (usually located under the seat or inside the C-pillar trim), oxidation from water ingress, or spread terminals causing increased contact resistance.
  • 2Abnormally high resistance or open circuit in the pretensioner internal igniter (blown internal bridgewire, damp or aged pyrotechnic charge). Standard resistance is usually 2.0-3.0Ω.
  • 3Prolonged bending and compression of the under-seat wiring harness causes broken wires or damaged insulation (common in passenger vehicles with frequent fore-and-aft seat adjustment).
  • 4Pretensioner connector not fully seated or wiring harness pinched during vehicle modifications (such as installing seat covers or floor mats) or accident repairs.
  • 5SRS control unit (ACU) internal detection circuit fault causing false abnormal resistance readings (rare; consider after ruling out wiring faults)
What To Do
  • 1
    Safety Preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds for the SRS capacitor to fully discharge. Read and record the DTC freeze frame data and confirm the fault frequency (current/history).
  • 2
    Visual inspection: Remove the right rear seat and lower C-pillar trim panel. Verify the pretensioner connector (usually yellow) is fully seated and check for water ingress, corrosion, or foreign objects. Inspect the wiring harness corrugated conduit under the seat for damage. Check the wires for crush marks from the seat rail.
  • 3
    Resistance measurement: Disconnect the pretensioner connector. Use a digital multimeter to measure the resistance on the pretensioner body side (Standard value: 2.0±0.2Ω, refer to the workshop manual for details). If the resistance is >3.6Ω or infinite, the pretensioner body is faulty. Replace the seat belt assembly (the pretensioner is a non-repairable part).
  • 4
    Wiring harness inspection: Measure continuity from the connector harness side to the SRS control unit to check for open circuits. Measure harness insulation to ground and power supply to rule out short circuits. If harness resistance is >1Ω or a short circuit exists, repair or replace the wiring harness.
  • 5
    System reset: After repair, reconnect all connectors and the battery. Use the diagnostic tool to clear the fault code and perform SRS system self-learning (required on some models). Perform a road test or simulation test to confirm B1772 does not return and the airbag warning lamp turns off normally.
Real-World Cases
BYD DTC AI Analysis

Oxidized right rear connector on BYD Song MAX causing high resistance

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Symptoms: Dashboard airbag warning light constantly illuminated; scan tool reporting DTC B1772. Diagnosis: Removed the right rear seat. Found obvious green corrosion inside the seatbelt pretensioner connector (yellow) with poor pin contact. Measured pretensioner body resistance at 2.1Ω (normal), but circuit resistance read 5.8Ω with the connector attached. Repair: Cleaned the connector pins with precision electrical contact cleaner, applied conductive protectant, and reinserted the connector firmly. Fault cleared.
BYD DTC AI Analysis

Seat rail crushed wiring harness causing B1772 in BYD Tang DM

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Symptoms: Airbag warning light illuminates intermittently on rough roads. Fault code B1772 (intermittent). Diagnosis: Found the seatbelt pretensioner harness beneath the right rear seat crushed by the seat rails. Damaged insulation caused internal wires to partially fracture (intermittent contact). Repair: Cut out the damaged section, soldered the wires, and sealed with heat-shrink tubing. Rerouted the harness to avoid interference with moving parts. Fault completely resolved.
BYD DTC AI Analysis

BYD Yuan EV: Replaced pretensioner assembly due to internal open circuit

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Symptoms: Airbag warning light stays on continuously; only current DTC B1772 present. Diagnosis: Disconnected the pretensioner connector and measured resistance directly across the pretensioner terminals—infinite resistance (open circuit). Wiring harness continuity and power supply both normal. Confirmed pretensioner internal igniter bridge wire blown or propellant failure. Resolution: Replaced the right rear seatbelt assembly (includes pretensioner) because the pretensioner is integrated with the seatbelt retractor. After installation, coded and configured the unit with a diagnostic tool. Cleared fault codes; system 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.