AU
B17171B

DTC B17171B indicates the SRS (Supplemental Restraint System) control module detects an open circuit in the left knee airbag (Driver Knee Airbag) igniter circuit — Atto 3

Safety System

DTC B17171B indicates the SRS (Supplemental Restraint System) control module detects an open circuit in the left knee airbag (Driver Knee Airbag) igniter circuit.

The resistance value falls outside the normal range (normal: approx. 2-3Ω; open circuit: >10Ω or infinite).

This fault indicates a physical break in the wiring or connector between the airbag ECU and the left knee airbag assembly, or an internal open circuit within the airbag igniter itself.

The knee airbag protects the driver's lower limbs from dashboard intrusion during a frontal collision.

This fault prevents the airbag from deploying during a crash and may trigger the SRS secondary protection mechanism (e.g., disabling the associated airbag group), posing a severe safety hazard.

In the BYD diagnostic protocol, the '1B' suffix specifically denotes an 'open circuit/high resistance' condition.

4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Knee airbag wiring harness connector loose or disconnected: Water ingress, vehicle modifications, or improper seating after repairs can cause poor contact at the yellow dedicated SRS connector located under the dashboard near the steering column.
  • 2Airbag igniter internal open circuit: Broken or aged igniter coil inside the knee airbag assembly, usually accompanied by damage to the airbag module itself. This commonly occurs after an accident without airbag replacement or when the airbag reaches the end of its service life (vehicles over 10 years old).
  • 3Physical damage to the wiring harness: Pedal operation, floor mat compression, or accident repairs pull the under-dash wiring harness, breaking the wire; or repeated bending in the sill harness transition area breaks the internal copper strands while leaving the insulation intact.
  • 4SRS ECU (airbag control module) internal fault: An ECU internal detection circuit fault triggers a false open circuit. However, this condition typically sets simultaneous fault codes for multiple airbags.
  • 5Clock spring or spiral cable related fault: On some models, the knee airbag wiring harness passes under the steering wheel. An internal open circuit in the clock spring may affect circuit detection (verify the specific model's wiring harness routing).
What To Do
  • 1
    Safety preparation: Switch the vehicle OFF, disconnect the 12V battery negative terminal, and wait at least 3 minutes to fully discharge the SRS capacitor and prevent accidental airbag deployment during repair.
  • 2
    Fault confirmation and freeze frame retrieval: Use a diagnostic tool such as VDS2000 or Launch PAD to read the complete fault codes and freeze frame data. Confirm whether the fault is current (Active) or historical (Historic). Record the vehicle status at the time of the fault.
  • 3
    Visual inspection: Remove the driver's side lower dashboard trim panel. Locate the left knee airbag assembly (inside the dashboard below the steering column). Verify the yellow SRS connector is fully seated and the connector locking tab is engaged. Inspect the wiring harness for obvious damage, crushing, or signs of water ingress.
  • 4
    Circuit continuity check: Disconnect the airbag connector. Use a multimeter to measure the airbag-side igniter resistance (standard value: 2.0±0.3Ω). If the resistance is infinite, replace the airbag assembly. Measure harness-side continuity from the airbag ECU to the connector. Check for open circuits or shorts to ground.
  • 5
    Insulation and contact check: Inspect connector terminals for oxidation, backed-out pins, or deformation. Measure wiring harness insulation resistance to ground (must be >1MΩ). Check the SRS ECU connector for looseness.
  • 6
    Component replacement: If the airbag assembly is faulty, replace it with a genuine left knee airbag (verify the part number by vehicle model, e.g., #... for the E2 model). Store the new airbag module flat and do not drop it. If the wiring harness is faulty, repair or replace the instrument panel wiring harness assembly.
  • 7
    System reset and verification: Reconnect all connectors and the battery. Use the diagnostic tool to clear the fault code. Perform the 'SRS system self-check' (usually requires turning the ignition switch to the ON position and waiting for the system self-check to complete). Verify B17171B does not return. Check that the instrument panel SRS warning light turns off after the self-check.
  • 8
    Function test (optional): At an authorized service center, use the dedicated tool to perform an 'SRS system simulation test' to verify the knee airbag circuit resistance is within the normal range and confirm the system readiness status is Complete.
Real-World Cases
BYD DTC AI Analysis

New vehicle PDI found knee airbag not connected.

✓
A 2020 BYD E3 arrived at the dealer with the SRS warning light on steadily during PDI. Scanning retrieved DTCs B17171B (left knee airbag not connected) and B17181B (right knee airbag not connected). Inspection traced the fault to an assembly omission: the yellow SRS connectors for both knee airbags had not been plugged in when the instrument panel was installed on the production line. After reconnecting the connectors and confirming the locks were fully seated, the technician cleared the codes. The SRS system then passed self-test, and the fault was eliminated. This case suggests possible assembly issues on E2/E3 models from that production period.
BYD DTC AI Analysis

Corroded knee airbag wiring harness in flood-damaged vehicle

✓
After driving through floodwater in heavy rain, a 2019 Qin EV displayed an airbag warning light on the instrument panel. The scan tool retrieved current fault code B17171B. Removing and inspecting the driver-side knee airbag connector revealed obvious water staining and green copper corrosion inside the plug. Water level exceeded the floor while wading, allowing moisture to enter the SRS connector through poor harness sealing. Repairs: cleaned connector terminals with electronic cleaner, applied special conductive grease, replaced the waterproof seal, and waterproofed the harness. After repair, resistance returned to normal. Cleared the fault code, and it did not return.
BYD DTC AI Analysis

Loose connection in airbag circuit after accident repair

✓
A BYD E2 had a collision. During replacement of the front bumper and instrument panel, the repair technician removed the left knee airbag. After repairs, the technician did not clear the fault codes. Three days after delivery to the customer, the SRS warning light illuminated. Inspection found that although the knee airbag connector was plugged in, the locking tab had not fully engaged. Vehicle vibration caused an intermittent connection, triggering an intermittent B17171B fault. After reconnecting the connector and hearing a locking click, the technician used a diagnostic tool to perform 'Crash Data Clear' and 'SRS Configuration Write', permanently resolving the fault.
BYD DTC AI Analysis

Wiring harness wear caused an intermittent open circuit.

✓
An E3 with 80,000 km had an intermittent SRS warning light. The scan tool showed stored fault code B17171B. Inspection found the wiring harness under the dashboard chafing on the edge of the steering column mounting bracket. The damaged insulation caused the internal copper strands to partially fracture, opening the circuit at certain steering angles or when the body flexed. Repair: Spliced in a replacement wire (minimum 0.5mm², high-temperature grade), rerouted the harness to clear the interference point, wrapped the section with fleece tape and corrugated tubing, and repositioned the harness clips to provide enough slack.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.