AU
B1793

This DTC indicates the Airbag Control Module (ACM) detects the driver-side second-stage seatbelt pretensioner circuit resistance exceeds the calibrated range (typically 2-5 ohms) — Seal U

Safety System

This DTC indicates the Airbag Control Module (ACM) detects the driver-side second-stage seatbelt pretensioner circuit resistance exceeds the calibrated range (typically 2-5 ohms).

This Passive Safety System (SRS) circuit fault indicates high resistance or an open circuit in the pretensioner circuit.

The pretensioner is a critical protective device that uses a pyrotechnic charge to instantly tighten the seatbelt during a collision.

This fault indicates the driver-side seatbelt may fail to pretension correctly during a frontal collision, increasing occupant forward travel, reducing restraint system effectiveness, and posing a severe safety hazard.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Open circuit, aging, or increased resistance in the driver seat belt pretensioner internal coil.
  • 2Loose connection, backed-out pins, oxidation, or water ingress at the pretensioner wiring harness connector (yellow plug) under the seat, causing increased contact resistance.
  • 3Long-term bending and wear of the pretensioner wiring harness at the seat slide rail causes internal wire breakage or a partial open circuit.
  • 4Vehicle water ingress or high humidity causes corrosion on the pretensioner connector terminals, forming an oxide layer that increases resistance.
  • 5Airbag Control Module (ACM) internal sampling circuit fault or software calibration error (uncommon)
What To Do
  • 1
    Use the dedicated diagnostic tool to read the fault code. Confirm whether B1793 is a current (Active) or history (History) fault, and record the resistance value from the freeze frame data.
  • 2
    Disconnect the 12 V battery negative terminal and wait at least 90 seconds for the airbag system capacitor to fully discharge (follow safety operating procedures).
  • 3
    Check the airbag wiring harness connector under the driver’s seat (yellow-marked plug) for looseness, backed-out pins, oxidation, or signs of water ingress. Clean the terminals with electrical contact cleaner, apply conductive grease, and reconnect.
  • 4
    Remove the driver seat. Inspect the pretensioner wiring harness insulation for wear at the seat slide rail bend. Measure wiring harness continuity and resistance between the connector and the pretensioner.
  • 5
    Disconnect the pretensioner connector and use a multimeter to measure the resistance of the pretensioner unit (normal range: 2-5Ω). If the resistance is infinite or >5Ω, the pretensioner unit is faulty. Replace the driver seat belt pretensioner assembly.
  • 6
    Measure wiring harness continuity between the pretensioner connector and the Airbag Control Module (ACM). Specifically inspect the floor harness junction. Repair high-resistance or open-circuit points. Replace the wiring harness if necessary.
  • 7
    Reinstall the seat and all connectors. Ensure the wiring harness does not interfere with the seat slide rail throughout its full range of travel. Connect the battery, clear the fault code, and perform a system self-check (turn the ignition switch to the ON position and verify the SRS warning lamp turns off normally).
  • 8
    Perform a road test or simulate seat forward and backward movement and vibrations to confirm the fault code does not return and the system resumes normal operation.
Real-World Cases
BYD DTC AI Analysis

BYD Song MAX: Loose connection in wiring harness under seat caused SRS fault.

✓
Symptoms: Airbag warning light stays illuminated. Scanned and retrieved restraint system fault codes. Vehicle has no collision history; warning light remains on. Diagnosis: Checked wiring harness connector under driver's seat. Found loose connection with oxidized pins; measured contact resistance >10Ω. Inspected wiring at seat rails; no mechanical damage. Repair: Cleaned and re-secured seat harness connector, sanded terminals to remove oxidation, applied conductive grease to prevent further oxidation, cleared fault codes. Warning light extinguished; system returned to normal.
BYD DTC AI Analysis

BYD F3 Seat Belt Buckle Switch Circuit Fault (similar to B2692 case)

✓
Symptoms: Airbag warning light illuminates intermittently after startup with beeping alarm. No obvious correlation with driver seatbelt use; occurs occasionally on rough roads. Diagnosis: Scan tool retrieved seatbelt buckle switch circuit fault from airbag system. Wiring harness beneath driver seatbelt buckle showed internal conductor breakage from long-term flexing. Seatbelt buckle switch had intermittent contact. Resolution: Replaced driver seatbelt buckle assembly (with switch), repaired broken harness and added protective sleeve. Cleared codes with scan tool; road test confirmed warning light and alarm no longer occur.
Original source ↗
BYD DTC AI Analysis

BYD Tang: Water ingress in seat belt pretensioner connector caused corrosion and high resistance.

✓
Symptoms: Airbag warning light stayed on after driving through water. Scan tool retrieved DTC B1793 for high resistance in the driver's second-stage seatbelt pretensioner. Diagnosis: Removed the driver's seat and found the pretensioner connector (yellow waterproof plug) had water staining and green copper corrosion inside. The pretensioner body measured 3.2Ω (normal), but resistance through the harness read infinite with the connector attached. Corroded terminals were causing an open circuit. Repair: Replaced the connector terminals, dried and resealed the plug, applied conductive grease, and reconnected. Cleared the codes and the system returned to normal. Recommendation: Inspect the floor sealing strips to prevent water ingress.
Other Seal U 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.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.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.
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.