AU
B1795

DTC B1795 indicates a short to B+ in the driver-side seat belt pretensioner Stage 2 squib circuit — Atto 8

Safety System

DTC B1795 indicates a short to B+ in the driver-side seat belt pretensioner Stage 2 squib circuit.

In the BYD SRS system, the seat belt pretensioner uses a dual-stage ignition design: Stage 1 triggers early in a collision to provide basic tightening force, and Stage 2 triggers during a severe collision to generate greater tightening force to better restrain the occupant.

This DTC indicates the airbag control unit (ACU) detects an abnormal voltage increase in the Stage 2 pretensioner circuit to near battery voltage (12V) and an abnormal resistance value.

This fault prevents the pretensioner from deploying correctly during a collision because the short to power prevents the firing current from forming a complete circuit.

It may also damage the ignition driver chip inside the ACU.

Because this is an active safety system fault, the vehicle illuminates the airbag warning lamp and may fail to protect the driver properly during a collision.

5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Damaged wiring harness sheath under the driver's seat or B-pillar pretensioner exposes copper wire that contacts body power supply wires (such as seat heating or power adjustment wires), causing a short circuit.
  • 2Water ingress, oxidation, or deformed terminals in the pretensioner connector (usually located under the seat or inside the B-pillar trim), causing a short to power between terminals.
  • 3Insulation breakdown in the seat belt pretensioner squib causes a short circuit between the internal coil and the housing, which indirectly connects to the vehicle power supply via the bracket.
  • 4Installer pierced the wiring harness during vehicle modifications (such as adding seat ventilation, heating, or audio equipment), shorting the pretensioner circuit to the constant power circuit.
  • 5Internal ignition drive transistor breakdown in the SRS control unit causes a continuous high-level signal at the output terminal (less common but requires inspection).
What To Do
  • 1
    Safety preparation: Turn off the vehicle, disconnect the negative battery terminal, and wait at least 3 minutes to fully discharge the SRS capacitor and prevent accidental airbag deployment during repair.
  • 2
    Visual inspection: Remove the driver's seat (keep the wiring harness connected) and the left B-pillar lower trim panel. Inspect the pretensioner wiring harness (typically in a yellow sleeve) for wear, cuts, or burn marks. Focus on the seat slide rail friction points and the wiring harness retaining clips.
  • 3
    Resistance measurement: Disconnect the pretensioner connector. Use a digital multimeter to measure the resistance between the two terminals on the pretensioner body. The normal value is 2.0-3.0 Ω. If the resistance is too low or infinite, replace the pretensioner.
  • 4
    Voltage measurement: Keep the pretensioner disconnected. Connect the red multimeter probe to the positive terminal on the pretensioner wiring harness side and the black probe to ground. Turn the ignition switch to the ON position. The multimeter should display 0V. If the multimeter displays battery voltage, this confirms a short to power.
  • 5
    Wiring harness isolation test: Strip back the corrugated conduit section by section along the harness routing. Use an oscilloscope or multimeter to monitor the circuit while wiggling the harness to locate the short circuit. Focus inspection on the intersection between the under-seat wiring harness and the seat heating/ventilation power wire.
  • 6
    Swap verification: Swap the driver-side and passenger-side pretensioner connections (verify the left and right part numbers are identical for the vehicle model). Clear the fault code and road test the vehicle. If the fault code changes to B17A5 (passenger-side second-stage short circuit), the pretensioner itself is faulty. If it remains B1795, the wiring harness or ACU is faulty.
  • 7
    Repair procedure: If the wiring harness is damaged, repair with heat-shrink tubing and reroute to prevent interference; if water entered the connector, clean, dry, and apply conductive grease; if the pretensioner or ACU is faulty, replace with genuine parts.
  • 8
    System reset: Connect all components, connect the battery, and use the diagnostic tool to clear the fault code. Perform 'SRS System Self-Learning' and 'Crash Sensor Calibration' (if required). Confirm the fault code does not reappear and the airbag warning light turns off.
Real-World Cases
BYD DTC AI Analysis

Seat adjuster chafed wiring harness causing short circuit

✓
2021 BYD Tang DM, 32,000 km. Airbag warning light on. Scanner read DTC B1795. Removing the driver's seat revealed the pre-tensioner harness bundled with the seat heater power wire underneath. Repeated seat adjustments wore through the harness sheath, shorting the pre-tensioner circuit to the heater constant live. Repair: Separated the harnesses, fixed the damage with double-layer heat shrink tubing, re-routed the wiring away from the seat rails, and added a protective sleeve. Fault resolved.
BYD DTC AI Analysis

Water ingress during car wash caused connector corrosion

✓
2019 BYD Yuan EV. Owner reported the airbag warning light illuminated after a car wash. Scan revealed DTC B1795. Inspection found the sealing ring on the pre-tensioner connector beneath the driver's seat had deteriorated. Water entered the connector during the wash, causing electrolytic corrosion between the terminals that created a short-circuit path. Replaced the connector housing and terminals, cleaned the wiring harness, applied waterproof silicone grease inside the connector, and rewrapped with waterproof tape. Fault has not returned.
BYD DTC AI Analysis

Internal short circuit in pretensioner assembly

✓
2020 Qin Pro (petrol). DTC B1795 appeared after accident repairs. The vehicle had sustained frontal impact damage; the front bumper and airbags were replaced, but the driver's seatbelt pretensioner was only reset, not replaced. Inspection revealed the pretensioner's internal secondary squib was damaged in the initial collision, breaking the insulation and causing a short to power. Replaced the OEM driver's seatbelt assembly (including pretensioner) to resolve the fault. Note: Replace pretensioners after deployment; never simply clear the fault codes.
BYD DTC AI Analysis

Aftermarket seat installation punctured the wiring harness.

✓
2019 Song MAX. Fault appeared after owner fitted leather seat upholstery and a ventilation system. Technicians found staples securing the seat cover had pierced the pretensioner harness and the seat ventilation motor power wire, causing a short. Replaced the damaged harness section. Pretensioner tested undamaged. Re-routed wiring to specification, avoiding staple locations.
BYD DTC AI Analysis

SRS control unit internal fault

✓
2021 Tang. Intermittent B1795, sometimes appearing on cold startup but disappearing when warm. Wiring harness and pretensioner tested normal. Suspected poor thermal stability of ACU internal secondary ignition drive circuit. Swapped ACU from normal vehicle for testing; fault transferred. Replaced airbag control unit and recoded to match. Fault eliminated.
Other Atto 8 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.