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 8

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 8 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. This may prevent full pretensioner operation 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.
5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Loose or disconnected yellow SRS connector under the seat: Frequent driver seat adjustments loosen the pretensioner harness plug (usually located inside the seat rail). On 2017-2018 Qin series models, the seat slide rail design provides insufficient harness length. Repeated forward and backward movement often partially disconnects the plug.
  • 2Wiring harness worn or broken: Burrs on the seat frame edge cut through the pretensioner wiring harness insulation, or frequent seat height adjustment causes metal fatigue and breakage of the wiring harness at bend points, resulting in an intermittent open circuit.
  • 3Terminal oxidation causing poor contact: 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 may trigger the fault).
  • 4Pretensioner body internal open circuit: Open circuit in the seat belt retractor igniter (squib) internal coil. This typically results from manufacturing defects or cracked solder joints due to long-term vibration.
  • 5SRS control unit monitoring circuit fault: The internal ACU (Airbag Control Unit) monitoring chip for the driver's second-stage pretensioner is damaged, causing a false open-circuit fault. Perform a cross-check to isolate the fault.
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 the complete fault codes. Confirm B1794-00 is a current fault (Active) rather than a historical fault. Record the freeze frame data to 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). Check if the yellow 2-pin SRS connector under the seat frame (marked DAB-Pretensioner-Stage2) is fully locked. Confirm the connector locating pin is intact 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; remove the lower instrument panel trim) and the pretensioner connector. Measure continuity between both ends of the wiring harness. Resistance must be less than 1 Ω. If resistance exceeds 2 Ω, repair the wiring harness. Measure the insulation resistance to ground. Resistance must exceed 10 MΩ to prevent a short circuit.
  • 4
    Component replacement verification: If wiring harness continuity is normal, bridge the pretensioner connector with a 2.7Ω dedicated service resistor (BYD part number BYD-SRS-TEST-01). Clear the fault code and power on the vehicle. 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 within the 2.0-3.0Ω range.
  • 5
    System reset and calibration: After installing the seat, restore all connections. Use the diagnostic tool to perform 'SRS system configuration' (requires 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 'historical fault', then delete the code. Finally, perform an 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 ensure 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 and observe the resistance value. It must remain stable between 2.0-3.0Ω without fluctuation or sudden jumps.
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 8 Fault Codes
B110811This DTC indicates a short circuit in the air conditioning system PM2.5 air quality sensor (rapid detector). Specifically, abnormal continuity exists between the sensor power supply circuit or signal output circuit and body ground or battery positive. This causes the control module (ACU/air conditioning controller) to detect abnormal current or a voltage signal outside the valid range (typically 0V or supply voltage). The PM2.5 sensor monitors internal and external particulate concentrations, providing the data the automatic air conditioning system uses to switch between fresh air and recirculation modes. A short circuit disables the air quality monitoring function. This fault may force the air conditioning system into recirculation protection mode and trigger related thermal management system faults, as the air conditioning system acts as a key actuator in vehicle thermal management. In severe cases, the short circuit current can damage the internal sampling circuit of the air conditioning controller or overheat the wiring harness.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.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.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.