AU
B1794-00

DTC B1794-00 indicates the SRS (Supplemental Restraint System) control unit detects an open circuit or abnormal resistance (typically greater than 10Ω or less than 1Ω) in the driver-side seat belt pretensioner second-stage deployment circuit — Seal U

Safety System

DTC B1794-00 indicates the SRS (Supplemental Restraint System) control unit detects an open circuit or abnormal resistance (typically greater than 10Ω or less than 1Ω) in the driver-side seat belt pretensioner second-stage deployment circuit.

The BYD Qin series dual-stage airbag system features a seat belt pretensioner with a dual-stage igniter.

This igniter tightens the seat belt in stages based on collision severity (first stage at approximately 30% force, second stage at 100% force).

This fault signifies the second-stage deployment circuit cannot form an effective closed circuit.

As a result, the second-stage pretensioning function fails during a severe collision, leaving only first-stage protection active.

The SRS control unit determines connection status by continuously monitoring circuit resistance (normally 2.0-3.0Ω).

When the unit detects an open circuit or high resistance, it stores this code and illuminates the airbag warning light.

The B1794-00 fault code on the Seal U indicates a problem in the driver-side seat belt pretensioner second-stage deployment circuit, usually due to an open circuit or abnormal resistance. Severity is medium because reduced pretensioner protection may occur in a severe crash. Common causes include a loose yellow SRS connector under the seat or damaged wiring from seat movement. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Loose or disconnected yellow SRS connector under the seat: Frequent driver seat adjustments loosen the pretensioner harness plug (usually located inside the seat rail). Specifically, the 2017-2018 Qin series seat rail design provides insufficient harness length, causing long-term forward and backward movement to partially disconnect the plug.
  • 2Wiring harness wear or breakage: Seat frame edge burrs cut through the pretensioner wiring harness insulation, or frequent seat height adjustment causes metal fatigue and breakage at harness bends, resulting in an intermittent open circuit.
  • 3Terminal oxidation causing poor contact: Driving through water or damp conditions oxidizes the internal terminals of the pretensioner connector (usually a yellow waterproof plug), increasing contact resistance (exceeding 5Ω can trigger the fault).
  • 4Pretensioner body internal open circuit: The seat belt retractor igniter (Squib) internal coil has an open circuit. Manufacturing defects or cracked solder joints from long-term vibration typically cause this.
  • 5SRS control unit monitoring circuit fault: The internal monitoring chip in the ACU (Airbag Control Unit) for the driver second-stage pretensioner is damaged, falsely reporting an open circuit fault. Isolate the fault using the cross-check method.
What To Do
  • 1
    Safety Preparation and Diagnostic Confirmation: Disconnect the 12V battery negative terminal and wait at least 90 seconds to fully discharge the SRS capacitor. Use a BYD VDS2000 or Launch X431 diagnostic tool to read all fault codes. Confirm B1794-00 is a current (Active) fault, not a historical fault. Record the freeze frame data to check the circuit resistance value (values above 10.8Ω typically indicate an open circuit).
  • 2
    Visually inspect the connector: Remove the driver's seat (4 retaining bolts, 25 N·m torque). Verify the yellow 2-pin SRS connector under the seat frame (marked DAB-Pretensioner-Stage2) is fully locked. Confirm the connector locating pin is not broken and the locking tab engages fully (listen for a 'click'). Inspect the wiring harness corrugated conduit for damage.
  • 3
    Circuit continuity test: Set a multimeter to the resistance setting. Disconnect the SRS control unit connector (located under the lower center console; remove the auxiliary instrument panel) and the pretensioner connector. Measure the continuity between both ends of the wiring harness. Normal resistance is less than 1Ω. If the resistance is greater than 2Ω, repair the wiring harness. Measure the insulation resistance to ground. The resistance must be greater than 10MΩ; otherwise, a short circuit risk exists.
  • 4
    Component replacement verification: If wiring harness continuity is normal, bridge the pretensioner connector using a 2.7Ω dedicated service resistor (BYD part number BYD-SRS-TEST-01). Clear the fault code and power on. If the fault code disappears, the pretensioner is faulty. Replace the driver seat belt retractor assembly (including the pretensioner). Verify the new part resistance is 2.0-3.0Ω.
  • 5
    System reset and calibration: After installing the seat, restore all connections. Use the diagnostic tool to execute 'SRS system configuration' (requires entering the vehicle VIN and configuration code). Clear the fault codes and perform a 'system self-check' (takes approximately 30 seconds). Confirm the B1794-00 status changes to 'history fault', then delete the code. Finally, perform an airbag warning light cycle test (normal operation: light turns off 6 seconds after power-on).
  • 6
    Function verification: Use the diagnostic tool to perform a 'Crash Record Check' to verify no historical crash data interference. Perform a 'Pretensioner Circuit Resistance Monitoring' live data stream test. Move the seat forward and backward to the limit positions. Verify the resistance value remains stable between 2.0-3.0 Ω without fluctuation or jumping.
Real-World Cases
BYD DTC AI Analysis

Worn seat wiring harness caused intermittent open circuit in Qin EV450

✓
Vehicle arrived with the airbag warning light intermittent; fault frequency increased after driving over speed bumps. DTC B1794-00 present. Resistance fluctuated between 2.1Ω and 12.5Ω when moving the seat. Removed the seat and found the pre-tensioner harness insulation worn through at the seat height adjuster pivot, with 90% of the internal copper wires fractured. Repair: Cut out the damaged harness section, extended with identical high-temperature wire (FLRY-B 0.35mm²) using soldered joints, applied double-layer heat-shrink insulation, and secured the wiring route to avoid interference with moving components. No recurrence at 3-month follow-up.
BYD DTC AI Analysis

BYD Qin 100 pretensioner connector oxidised after water wading

✓
Customer reported the airbag warning light remained on after driving through approximately 30 cm of water (submerging the carpet). Testing found DTCs B1794-00 and B1795-00 (Stage 2 short circuit) both present. Disconnected the SRS connector under the driver's seat and found water stains and green corrosion inside the yellow plug. Insulation resistance between terminals had dropped to 0.5 MΩ. Repair: Thoroughly cleaned the connector with electronic cleaner, sanded the terminals with 800-grit paper to bright metal, sprayed WD-40 Precision Electrical Cleaner, replaced the waterproof seal ring, applied silicone-free conductive paste, and reconnected. After clearing the fault codes, resistance returned to 2.3 Ω.
BYD DTC AI Analysis

Pretensioner connector not connected after seat replacement

✓
Owner replaced second-hand salvage seats without disconnecting the battery; instrument cluster showed airbag warning. Diagnosis found active fault code B1794-00 with live data reading infinite resistance. Inspection found the pretensioner connector completely disconnected during the seat swap, and the connector lock tab snapped due to age. Replaced the OEM SRS connector (part number BYD-SRS-CONN-02). Re-crimped the terminals using the crimping tool's dedicated die (crimp height 0.8mm, pull test ≥50N). Verified the secondary locking mechanism intact. Ran SRS system reconfiguration to clear the fault. Advised customer to always disconnect the negative battery terminal before removing or installing seats in the future.
BYD DTC AI Analysis

Open circuit in pretensioner internal coil

✓
2017 BYD Qin 80, accident repair (front collision, airbags deployed). Installed a new driver seatbelt assembly but B1794-00 remained. Old unit measured ∞ (confirmed deployed). New unit measured 2.4Ω on the bench, but the scan tool read 10.2Ω in the car. Step-by-step harness checks showed no faults. The new part turned out to be aftermarket—its plug terminals had excessive clearance in the BYD OEM socket, causing poor contact. Fix: Installed a BYD genuine seatbelt retractor (part number 5A-5813100). Fault cleared immediately. Use only genuine SRS components; aftermarket parts may have incorrect terminal plating and dimensional tolerances.
BYD DTC AI Analysis

SRS control unit false positive (software bug)

✓
Multiple Qin EV300s threw B1794-00 codes, but pretensioner resistance measured normal (2.2Ω), continuity tested good, and wiggling the harness changed nothing. BYD technical service bulletin TSB-SRS-2018-03 confirms early ACU software (below V1.2.1) falsely reports second-stage pretensioner open-circuit faults in cold conditions (<5°C). Fix: Flash the SRS control unit to V1.3.0 using the VDS diagnostic tool (online programming takes ~15 minutes). After the update, 10 cold-start tests did not reproduce the fault. This case reminds us to check software versions rather than just replacing hardware.
Other Seal U Fault Codes
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.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.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.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.