AU
B17701A

This DTC indicates the Airbag Control Unit (ACU) detects a 0-ohm resistance in the right rear seatbelt pretensioner circuit — Atto 3

Safety System

This DTC indicates the Airbag Control Unit (ACU) detects a 0-ohm resistance in the right rear seatbelt pretensioner circuit.

As a key actuator in the passive safety system, the pretensioner contains an internal squib with a normal resistance of 1.5-3.0 Ω for circuit integrity monitoring.

A resistance of 0 indicates a hard short in the circuit.

Possible causes include a burned internal coil causing an inter-turn short, a wiring harness short to ground (vehicle body), or shorted connector pins.

This fault prevents the ACU from sending a firing command to the pretensioner during a collision or triggers a system protection strategy that disables the entire right-side airbag circuit, severely compromising restraint protection for the right rear passenger during an accident.

The B17701A fault code on the Atto 3 indicates a short circuit in the right rear seatbelt pretensioner circuit, with the Airbag Control Unit detecting 0-ohm resistance instead of the normal range. Severity is medium, as this may disable pretensioner or right-side airbag protection. Common causes include an internal pretensioner igniter short or damaged wiring under the seat/B-pillar. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Right rear seat belt pretensioner internal igniter burned out or coil inter-turn short circuit (commonly due to seal failure after water ingress or pretensioner aging).
  • 2Worn insulation on the pretensioner wiring harness under the seat or inside the B-pillar, causing the positive and negative wires to short to ground (common from frequent seat movement or improperly secured harnesses during modifications).
  • 3Poor sealing of the yellow dedicated connector (usually located under the seat or inside the B-pillar trim) allows water ingress, causing electrolytic corrosion and a short circuit between pins.
  • 4Airbag Control Unit (ACU) internal monitoring circuit fault or damaged sampling resistor causing a false 0 ohm reading.
  • 5Failure to replace a deployed pretensioner after a collision, or directly measuring the pretensioner using the resistance setting on a multimeter during repair (output current from some digital multimeters may damage the squib, causing an internal short circuit).
What To Do
  • 1
    Safe power-down: Turn off the ignition, disconnect the 12V battery negative terminal, and wait at least 5 minutes to fully discharge the SRS backup power supply capacitor and prevent accidental airbag deployment.
  • 2
    Fault Confirmation: Use a dedicated BYD diagnostic tool (such as ED400 or VDS) to read the freeze frame data. Confirm B17701A is a current fault (Active) rather than a history fault (History). Record the vehicle status at the time of the fault.
  • 3
    Physical location: Remove the right rear seat cushion and lower B-pillar trim panel. Locate the pretensioner at the right rear seat belt retractor (with the yellow keyed connector). Check the connector for visible damage or signs of water ingress.
  • 4
    Pretensioner unit inspection: Disconnect the yellow connector. Use a dedicated SRS high-impedance tester or a low-power ohmmeter (<10mA output) to measure the resistance between the two pins on the pretensioner side. The normal value is 1.5-3.0 Ω. A reading of 0 Ω indicates an internal short circuit in the pretensioner; replace the seat belt assembly (do not replace the pretensioner separately).
  • 5
    Harness insulation check: With the connector disconnected, measure the resistance between each of the two pins on the harness side (ACU side) and body ground (should be >1MΩ), and measure the resistance between the two pins (should be >1MΩ). A reading of 0Ω or low resistance indicates a short circuit in the harness.
  • 6
    Wiring repair: Carefully inspect the pretensioner wiring harness route (usually along the seat rail and sill trim to the center console) for abrasion or crush marks. Focus on the harness fixing points within the seat's fore-and-aft travel range. Repair damaged insulation and rewrap the harness. Replace the wiring harness if necessary.
  • 7
    Connector handling: If water entered the connector, thoroughly clean it with electrical contact cleaner, blow dry with compressed air, apply conductive grease, and reconnect. Check pins for bending or backing out. Replace the connector housing if necessary.
  • 8
    System reset and verification: Restore all connections, reconnect the negative battery terminal, and clear the fault code. Turn the ignition switch to the ON position and observe the SRS warning lamp; it must turn off after the self-check. Use a diagnostic tool to perform the 'SRS System Self-check' or 'Configuration and Calibration' procedure and confirm B17701A does not return.
Real-World Cases
BYD DTC AI Analysis

Internal short in right rear pretensioner causing SRS light to stay on

✓
2019 BYD Qin EV, 82,000 km. SRS warning light on the instrument cluster stayed on. Scan tool retrieved DTC B17701A (right rear seatbelt pretensioner resistance: 0 Ω). Removed the right rear seat and found visible oxidation on the yellow connector of the seatbelt pretensioner (mounted at the retractor). Disconnected the connector and measured the pretensioner body resistance at 0.1 Ω, determining the internal squib burned and short-circuited. Replaced the right rear seatbelt assembly (part number matched per VIN). Measured the new part resistance at 2.3 Ω. Cleared the fault codes; system returned to normal. Traced the root cause to possible water wading—water ingress into the pretensioner sealed cavity caused coil corrosion.
BYD DTC AI Analysis

Worn seat rail wiring harness causing intermittent short

✓
BYD E2 SRS warning light intermittent after frequent right rear seat removal for cargo hauling. Diagnosis: intermittent DTC B17701A. Inspection found the pretensioner harness chafed through at the seat rail retaining clip—long-term friction wore through the insulation, exposing copper that contacted the body metal and shorted to ground. Rerouted the harness clear of motion interference areas, wrapped it in abrasion-resistant corrugated tubing, and added a rubber sleeve. Fault resolved. Secure under-seat wiring properly to prevent wear from dynamic loads.
BYD DTC AI Analysis

Water ingress corroded the connector, causing abnormal resistance.

✓
Right rear floor carpet held water after the vehicle forded water. SRS logged code B17701A. The pretensioner connector beneath the seat contained muddy water; electrolyte bridging between pins caused a 0-ohm short. Cleaned the terminals, flushed the housing with electrical contact cleaner, and dried. Insulation resistance returned to normal. Cleared blocked rear body drain holes to eliminate water accumulation. Recommend inspecting floor wiring harness connector sealing on vehicles that have forded water.
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.