AU
B1799-00

DTC B1799-00 indicates the SRS (Supplemental Restraint System) ECU detects the front passenger-side second-stage seat belt pretensioner circuit resistance exceeds the normal upper limit (typically >3 — Qin Plus

Safety System

DTC B1799-00 indicates the SRS (Supplemental Restraint System) ECU detects the front passenger-side second-stage seat belt pretensioner circuit resistance exceeds the normal upper limit (typically >3.0-3.5Ω, normal range is 2.0-3.0Ω).

The second-stage pretensioner is a critical component of the airbag system.

During a severe collision, a pyrotechnic charge generates a rapid tightening force, working with the first-stage pretensioner to provide enhanced occupant restraint.

Excessive resistance typically indicates a high-resistance circuit contact, a partial open circuit, or an aging internal resistance wire within the pretensioner.

This causes the ECU to identify a pretensioner failure risk, illuminate the airbag warning light, and potentially disable the front passenger-side airbag and pretensioner functions.

During a collision, the second-stage pretensioner may fail to deploy properly, allowing excessive forward occupant movement and increasing injury risk.

The B1799-00 fault code on the Qin Plus indicates the SRS ECU has detected excessive resistance in the front passenger-side second-stage seat belt pretensioner circuit. This is a medium-severity safety issue that may affect pretensioner or airbag operation in a crash. Common causes include an aging pretensioner resistance element or damaged under-seat wiring from seat movement. 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 — Qin Plus
  • 1Seat belt pretensioner internal resistance element aging or near-open circuit: Long-term use or moisture ingress causes the pretensioner squib resistance wire to drift beyond the ECU monitoring threshold.
  • 2Mechanical damage to the under-seat wiring harness: When adjusting the front passenger seat forward or backward, the seat underside rubs against or pinches the frame-mounted pretensioner wiring harness, causing partial breakage of the internal copper wires or poor contact.
  • 3Poor connector connection: The pretensioner connector below the B-pillar or under the seat exhibits pin oxidation, looseness, water ingress corrosion, or a failed latch, causing increased contact resistance.
  • 4Non-genuine part resistance specification mismatch: The resistance value of an aftermarket seat belt assembly pretensioner installed during accident repairs does not match the factory calibration, or the repair used a wiring harness repair part with a different resistance value.
  • 5Excessive bending or improper securing of the wiring harness: Vehicle modifications (such as installing floor mats or seat covers) pinched the pretensioner wiring harness, or incorrect harness routing during accident repairs caused increased local resistance.
What To Do
  • 1
    Connect the VDS2000 or VDS6000 diagnostic tool to the vehicle, read the DTC B1799-00 status, confirm whether it is a current or history fault, and record the resistance value from the freeze frame data (typically 3.5-5.0Ω).
  • 2
    Disconnect the battery negative terminal and wait at least 90 seconds for the SRS backup power supply to fully discharge. This ensures safe operation and prevents accidental airbag deployment.
  • 3
    Locate the front passenger second-stage seat belt pretensioner (on Qin models, usually behind the lower B-pillar trim or at the seat frame connection). Visually inspect the connector for looseness, oxidized or discolored pins, and internal water stains or corrosion.
  • 4
    Use a multimeter to measure the resistance across the pretensioner terminals. The standard value is 2.0±0.1Ω to 3.0±0.1Ω (refer to the specific vehicle repair manual). If the measured value is >3.5Ω, proceed to the next troubleshooting step.
  • 5
    Disconnect the pretensioner connector and directly measure the pretensioner body resistance. If the resistance is normal (2.0-3.0Ω), check the wiring harness: inspect the harness near the seat slide rail fixing bolts and under the carpet for pinching or damage. Use a multimeter to measure harness continuity and resistance (should be <1Ω).
  • 6
    If the wiring harness is damaged, use a genuine wiring harness repair kit to replace the connector or repair the damaged wire. Verify solder joint resistance is <0.5Ω. Apply waterproof tape and corrugated conduit for added protection. If the pretensioner unit resistance is too high, replace the front passenger seat belt assembly (including the second-stage pretensioner) with a genuine part. Do not use aftermarket parts.
  • 7
    Reconnect all connectors. Ensure the connector locks fully engage (listen for a 'click'). Restore the battery connection.
  • 8
    Use the diagnostic tool to clear the fault code and perform the SRS system self-check procedure. Verify B1799-00 does not return. Read the data stream to confirm the pretensioner resistance value is within the normal range.
  • 9
    Perform a road test. Simulate bumpy road conditions and seat adjustments. Verify the airbag fault warning lamp remains off and the system returns to normal.
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM pretensioner internal resistance aging caused high resistance.

✓
At 80,000 km, the airbag warning light stayed on constantly. VDS read DTC B1799-00. The technician measured front passenger second-stage pretensioner resistance at 3.5Ω, outside the standard 2.0-3.0Ω range. The B-pillar lower harness connector showed no oxidation or looseness, and seat wiring had no damage. Diagnosed the fault as pretensioner internal resistance wire aging causing resistance drift. Replaced the OEM front passenger seatbelt assembly. Post-repair resistance measured 2.2Ω. Cleared the fault codes; system self-check passed and the warning light went out.
Original source ↗
BYD DTC AI Analysis

Song MAX seat track pinches wiring harness, causing intermittent high resistance

✓
Airbag warning light illuminates intermittently, typically on cold starts and clearing after driving some distance. VDS logged B1799-00 as an intermittent fault. The technician performed a harness wiggle test; wiggling the wiring beneath the passenger seat reproduced the fault. Disassembly revealed the seat rail mounting bolt crushing the seatbelt pretensioner harness, partially fracturing the internal copper wires. Contact resistance fluctuated between 2.5-4.5Ω with seat position changes. Repaired the damaged harness, rerouted the wiring clear of the seat rail travel range, and protected it with waterproof tape and corrugated tubing. Fault resolved.
Original source ↗
BYD DTC AI Analysis

Resistance mismatch in aftermarket parts after Qin EV accident repair

✓
After front collision repairs, the airbag warning light stayed on. VDS read B1799-00 (resistance too high) and B1798-00 (resistance too low). The passenger seatbelt assembly was an aftermarket part; the pretensioner measured 3.8Ω and the connector was loose. Replaced it with a genuine OEM unit, seated the connector fully and locked it, and measured 2.1Ω. Cleared the codes and the SRS self-test passed. Use genuine OEM SRS parts for accident repairs.
BYD DTC AI Analysis

Loose connector lock tab on Tang DM caused contact resistance fluctuation

✓
Airbag warning light intermittently illuminated on rough roads; normal on flat surfaces. VDS read B1799-00 as a history fault. Inspection found the passenger-side second-stage pretensioner connector lock loose—vehicle vibration caused slight plug displacement and poor contact. Oscilloscope monitoring caught resistance spiking to 4.2Ω during the fault. Replaced the pretensioner connector using a genuine wiring harness repair kit, secured the connection, and applied conductive grease to the pins to prevent oxidation. Road testing on rough surfaces after repair confirmed the fault cleared.
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.