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 — Atto 3

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 Atto 3 indicates a medium-severity SRS fault in the driver-side seat belt pretensioner second-stage circuit, usually due to an open circuit or abnormal resistance. Common causes include a loose yellow SRS connector under the seat or damaged pretensioner wiring from seat movement or wear. The airbag warning light may stay on. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Loose or disconnected yellow SRS connector under the seat: Frequent driver seat adjustment loosens the pretensioner harness plug (typically located inside the seat rail). Specifically, the 2017-2018 Qin series seat rail design provides insufficient harness length. Repeated forward and backward movement easily causes partial plug disconnection.
  • 2Harness wear or breakage: Seat frame edge burrs cut the pretensioner harness insulation, or frequent seat height adjustment causes harness metal fatigue and breakage at bend points, resulting in an intermittent open circuit.
  • 3Poor contact due to terminal oxidation: Driving through water or operating in humid environments 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 internal coil of the seat belt retractor squib has an open circuit. Manufacturing defects or solder joint cracking from long-term vibration typically cause this.
  • 5SRS control unit monitoring circuit fault: The ACU (Airbag Control Unit) internal monitoring chip for the driver's second-stage pretensioner is damaged, falsely reporting an open circuit. Isolate the fault using the cross-verification 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. Read all fault codes using a BYD VDS2000 or Launch X431 diagnostic tool. Confirm B1794-00 is an active fault, not a historical fault. Record freeze frame data and check the circuit resistance value (a reading above 10.8Ω typically indicates an open circuit).
  • 2
    Visually inspect the connector: Remove the driver's seat (4 retaining bolts, torque 25 N·m). 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 center console; requires removing the center console) and the pretensioner connector. Measure the wiring harness continuity between both ends. Normal resistance is less than 1 Ω. If the resistance exceeds 2 Ω, repair the wiring harness. Measure the insulation resistance to ground. The resistance must exceed 10 MΩ; 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 restore power. If the fault code disappears, the pretensioner itself is faulty. Replace the driver seat belt retractor assembly (including the pretensioner). Verify the new part resistance is within the 2.0-3.0Ω range.
  • 5
    System reset and calibration: After installing the seat, restore all connections. Use the diagnostic tool to execute 'SRS System Configuration' (requires vehicle VIN and configuration code). Clear the fault code and perform 'System Self-check' (takes approximately 30 seconds). Confirm the B1794-00 status changes to 'History Fault', then delete the code. Finally, perform the airbag warning lamp cycle test (normal: lamp turns off 6 seconds after power-on).
  • 6
    Function verification: Use the diagnostic tool to perform a 'Crash Record Check' to confirm no historical crash data interferes. Perform a 'Pretensioner Circuit Resistance Monitoring' real-time data stream test. Move the seat forward and backward to the limit positions and observe the resistance value. The resistance must remain stable between 2.0-3.0Ω with no fluctuation or sudden change.
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 Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.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.
Common problems reported for Atto 3 →Atto 3 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.