AU
B17701A

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

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.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Right rear seat belt pretensioner internal igniter burnout or coil inter-turn short circuit (commonly due to seal failure after vehicle wading or pretensioner aging).
  • 2Worn insulation on the pretensioner wiring harness under the seat or inside the B-pillar causes the positive and negative wires to short to ground (common during frequent seat movement or from unsecured 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 Ω reading.
  • 5Failure to replace a deployed pretensioner after an accident, or directly measuring the pretensioner using a multimeter resistance setting during repair (output current from some digital multimeters may damage the squib and cause 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 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) and not 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 yellow keyed connector). Inspect the connector exterior for 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. If the reading is 0 Ω, the pretensioner has an internal short circuit. Replace the seat belt assembly (the pretensioner cannot be replaced separately).
  • 5
    Harness insulation check: With the connector disconnected, measure the resistance from each pin on the harness side (ACU side) to body ground (should be >1MΩ). 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 routing (typically via the seat rail and door sill trim to the center tunnel) for wear 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, clean thoroughly with electrical contact cleaner, blow dry with compressed air, apply conductive grease, and reconnect. Check for bent or backed-out pins. Replace the connector housing if necessary.
  • 8
    System reset and verification: Restore all connections, reconnect the negative battery terminal, and clear the fault codes. Turn the ignition switch to the ON position and observe the SRS warning lamp; it should turn off after the self-check. Use a diagnostic tool to perform the 'SRS System Self-check' or 'Configuration and Calibration' procedure. Confirm B17701A does not reappear.
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 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.