AU
B1791-00

DTC B1791-00 indicates the driver-side Stage 2 Seatbelt Pretensioner resistance measures 0 ohms — Atto 8

Safety System

DTC B1791-00 indicates the driver-side Stage 2 Seatbelt Pretensioner resistance measures 0 ohms.

Normal pretensioner igniter resistance is 2.0-4.0 ohms.

A 0-ohm reading indicates a circuit Short to Ground or an internal short in the pretensioner squib.

This fault prevents the SRS control unit from triggering the Stage 2 Seatbelt Pretensioner during a collision (typically used for secondary tightening in severe impacts), compromising occupant restraint system effectiveness.

Additionally, the SRS warning lamp remains illuminated, the system enters fail-safe mode, and the airbags may fail to deploy.

The B1791-00 fault code on the Atto 8 indicates the driver-side Stage 2 seatbelt pretensioner circuit has 0 ohms resistance, suggesting a short to ground or an internal squib short. Severity is medium, as the SRS warning lamp may stay on and pretensioner or airbag operation could be affected. Common causes include a faulty pretensioner or damaged under-seat SRS wiring. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Pretensioner internal squib short circuit: Moisture, aging, or manufacturing defects cause an internal short circuit in the pretensioner ignition device, dropping resistance to 0 ohms.
  • 2Wiring harness worn and shorted to ground: Long-term friction and compression from seat movement damage the yellow SRS wiring harness under the driver’s seat, causing the wire to short to the vehicle body metal.
  • 3Connector water ingress and corrosion: Poor sealing of the seat pretensioner connector (usually located at the B-pillar or under the seat) allows water to enter after car washing or wading, causing a short circuit between pins.
  • 4ECU internal sampling circuit fault: A faulty internal A/D converter or sampling resistor in the SRS control unit incorrectly reads the pretensioner resistance as 0.
  • 5Improper repair operation: Failing to disconnect the battery when previously replacing the seat belt assembly caused a tool to short-circuit the pretensioner connector.
What To Do
  • 1
    Safety preparation: Disconnect the 12V battery negative terminal and wait at least 90 seconds (allowing the SRS capacitor to fully discharge) to prevent accidental airbag deployment.
  • 2
    Fault confirmation: Use a dedicated diagnostic tool (such as BYD ED400 or Launch X431) to read the fault code and confirm B1791-00 is a current fault (Active), not a history fault.
  • 3
    Visual inspection: Inspect the yellow SRS wiring harness sleeve under the driver's seat for damage. Check the connector (usually marked D21 or D22) for looseness, water ingress, or green copper corrosion.
  • 4
    Resistance measurement: Disconnect the SRS ECU connector (located under the center console or behind the center armrest) and the pretensioner connector. Measure the resistance on the pretensioner side using a multimeter. Normal resistance is 2-4 Ω. A reading of 0 Ω indicates an internal short circuit in the pretensioner.
  • 5
    Harness continuity check: Measure the resistance between the pretensioner connector harness side and body ground. The resistance should be infinite. A reading of 0 Ω indicates a short to ground. Strip the harness to locate the damaged point.
  • 6
    Insulation repair: If the wiring harness is damaged, wrap it with high-temperature insulating tape (≥125°C) or replace the SRS wiring harness assembly. If the connector has water ingress, clean it with electrical contact cleaner, blow dry, and apply conductive grease.
  • 7
    Component replacement: If the pretensioner resistance is 0 Ω, replace the driver seat belt assembly (including the pretensioner). Verify the new part resistance is within the standard range.
  • 8
    System verification: Reconnect all connectors and the battery, clear the fault code using the diagnostic tool, perform the SRS system self-check (ignition switch ON; the indicator should turn off), and test seat movement to verify it does not pinch the wiring harness.
Real-World Cases
BYD DTC AI Analysis

Qin EV450 seat movement caused wiring harness chafing and short circuit

✓
SRS warning light stayed on when the vehicle came in. Retrieved DTC B1791-00. Found the driver frequently adjusted the seat position, causing the seat rail edge to cut through the yellow SRS harness sleeve underneath. Exposed wires contacted the body and shorted to ground. Repair: Fixed the damaged harness (3 wires with damaged insulation, 1 completely severed), re-wrapped it with corrugated tubing, rerouted the harness, and added clips to prevent interference with the seat rails. Fault cleared after repair; no recurrence after 3 months of follow-up.
BYD DTC AI Analysis

Qin 80 pretensioner connector corroded after driving through water

✓
Customer reported the SRS warning light illuminated after heavy rain. DTC B1791-00 stored. Inspection confirmed water ingress; the carpet beneath the driver's B-pillar was damp. The pretensioner connector (D21) showed visible water stains and green oxidation. Resistance between pins measured 0.5Ω (short circuit). Diagnosis: Disassembled the connector and found the seal degraded. Cleaning the pins revealed electrolytic corrosion between pin 2 (ground) and pin 3 (signal) that created a micro-short. Repair: Replaced the connector assembly, treated the water-damaged harness section, applied waterproof silicone grease to the connector, and cleared the fault.
BYD DTC AI Analysis

Replaced rear seat belt pretensioner due to internal short circuit

✓
After accident repairs, the SRS warning light illuminated with DTC B1791-00. Service history showed the driver's seat belt assembly had just been replaced. The new pretensioner resistance measured 0.2Ω (abnormal); the old component measured 2.3Ω (normal) after disassembly. Root cause: The technician did not disconnect the battery during replacement. A wrench touched the pretensioner connector, causing momentary high current that burned out the pretensioner squib and created an internal short. Solution: Replaced the seat belt assembly under warranty and strictly followed SRS repair safety procedures (disconnect battery negative terminal first). Fault resolved.
BYD DTC AI Analysis

SRS ECU incorrectly detecting zero resistance

✓
Intermittent SRS warning light, DTC B1791-00. Static measurement showed pretensioner resistance of 2.8Ω (normal). Wiring harness insulation to ground tested good. Fault reoccurred on rough roads. Found loose connection at SRS ECU connector (inside dashboard) pin D21 (pretensioner signal). Oxidation caused unstable contact resistance; vibration triggered abnormal voltage sampling and the ECU misread it as 0Ω. Fix: Cleaned ECU connector pins, adjusted pin tension, applied conductive grease. No recurrence.
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.