AU
B1791-00

DTC B1791-00 indicates the driver-side Stage 2 Seatbelt Pretensioner resistance measures 0 ohms — Qin Plus

Safety System

DTC B1791-00 indicates the driver-side Stage 2 Seatbelt Pretensioner resistance measures 0 ohms.

Normal pretensioner igniter resistance is 2.0-4.0 ohms.

A 0-ohm reading indicates a circuit Short to Ground or an internal short in the pretensioner squib.

This fault prevents the SRS control unit from triggering the Stage 2 Seatbelt Pretensioner during a collision (typically used for secondary tightening in severe impacts), compromising occupant restraint system effectiveness.

Additionally, the SRS warning lamp remains illuminated, the system enters fail-safe mode, and the airbags may fail to deploy.

The B1791-00 fault code on the Qin Plus indicates a 0-ohm resistance reading in the driver-side Stage 2 seatbelt pretensioner circuit. This is a medium-severity SRS fault that can stop the pretensioner, and possibly airbags, from working correctly in a crash. Common causes include an internal pretensioner squib short or damaged under-seat SRS wiring shorted to ground. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1Pretensioner internal squib short circuit: Moisture, aging, or manufacturing defects cause an internal short circuit in the pretensioner ignition device, dropping resistance to 0 ohms.
  • 2Wiring harness worn and shorted to ground: Repeated seat movement chafes and pinches the yellow SRS wiring harness under the driver's seat, damaging the harness and shorting the wire to the vehicle body metal.
  • 3Connector water ingress and corrosion: Poor sealing of the pretensioner connector (usually located at the B-pillar or under the seat) allows water to enter after washing the vehicle or wading, causing a short circuit between pins.
  • 4ECU internal sampling circuit fault: A faulty internal A/D converter or sampling resistor in the SRS control unit causes the system to incorrectly read the pretensioner resistance as 0.
  • 5Improper repair procedure: Failure to disconnect the battery during previous seat belt assembly replacement; tool caused a short circuit at the pretensioner connector.
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.
  • 2
    Fault confirmation: Use a dedicated diagnostic tool (such as BYD ED400 or Launch X431) to read the fault code and confirm B1791-00 is a current fault (Active), not a history fault.
  • 3
    Visual inspection: Check the yellow SRS wiring harness sleeve under the driver's seat for damage. Check the connector (usually marked D21 or D22) for looseness, water ingress, or green corrosion.
  • 4
    Resistance measurement: Disconnect the SRS ECU connector (located under the center console or behind the center armrest) and the pretensioner connector. Use a multimeter to measure the resistance on the pretensioner side. Normal resistance is 2-4Ω. A reading of 0Ω indicates an internal short circuit in the pretensioner.
  • 5
    Harness continuity check: Measure the resistance between the harness side of the pretensioner connector and body ground. The resistance should be infinite. If it is 0 Ω, the harness is shorted to ground. Strip the harness to find the damaged point.
  • 6
    Insulation repair: If the wiring harness is damaged, wrap it with high-temperature insulating tape (≥125°C) or replace the SRS wiring harness assembly. If the connector has water ingress, clean it with electronic cleaner, blow dry, and apply conductive grease.
  • 7
    Component replacement: If the pretensioner resistance is 0 Ω, replace the driver seat belt assembly (including the pretensioner). Verify the resistance of the new part is within the standard range.
  • 8
    System verification: Reconnect all connectors and the battery, use the diagnostic tool to clear the fault code, perform an SRS system self-check (ignition switch ON; indicator lamp should turn off), and perform a seat movement test to verify the seat does not pinch the wiring harness.
Real-World Cases
BYD DTC AI Analysis

Qin EV450 seat movement caused wiring harness chafing and short circuit

✓
SRS warning light stayed on when the vehicle came in. Retrieved DTC B1791-00. Found the driver frequently adjusted the seat position, causing the seat rail edge to cut through the yellow SRS harness sleeve underneath. Exposed wires contacted the body and shorted to ground. Repair: Fixed the damaged harness (3 wires with damaged insulation, 1 completely severed), re-wrapped it with corrugated tubing, rerouted the harness, and added clips to prevent interference with the seat rails. Fault cleared after repair; no recurrence after 3 months of follow-up.
BYD DTC AI Analysis

Qin 80 pretensioner connector corroded after driving through water

✓
Customer reported the SRS warning light illuminated after heavy rain. DTC B1791-00 stored. Inspection confirmed water ingress; the carpet beneath the driver's B-pillar was damp. The pretensioner connector (D21) showed visible water stains and green oxidation. Resistance between pins measured 0.5Ω (short circuit). Diagnosis: Disassembled the connector and found the seal degraded. Cleaning the pins revealed electrolytic corrosion between pin 2 (ground) and pin 3 (signal) that created a micro-short. Repair: Replaced the connector assembly, treated the water-damaged harness section, applied waterproof silicone grease to the connector, and cleared the fault.
BYD DTC AI Analysis

Replaced rear seat belt pretensioner due to internal short circuit

✓
After accident repairs, the SRS warning light illuminated with DTC B1791-00. Service history showed the driver's seat belt assembly had just been replaced. The new pretensioner resistance measured 0.2Ω (abnormal); the old component measured 2.3Ω (normal) after disassembly. Root cause: The technician did not disconnect the battery during replacement. A wrench touched the pretensioner connector, causing momentary high current that burned out the pretensioner squib and created an internal short. Solution: Replaced the seat belt assembly under warranty and strictly followed SRS repair safety procedures (disconnect battery negative terminal first). Fault resolved.
BYD DTC AI Analysis

SRS ECU incorrectly detecting zero resistance

✓
Intermittent SRS warning light, DTC B1791-00. Static measurement showed pretensioner resistance of 2.8Ω (normal). Wiring harness insulation to ground tested good. Fault reoccurred on rough roads. Found loose connection at SRS ECU connector (inside dashboard) pin D21 (pretensioner signal). Oxidation caused unstable contact resistance; vibration triggered abnormal voltage sampling and the ECU misread it as 0Ω. Fix: Cleaned ECU connector pins, adjusted pin tension, applied conductive grease. No recurrence.
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.