AU
B171E-00

DTC B171E-00 indicates the driver-side knee airbag ignition circuit resistance exceeds the normal threshold range (typically 1 — Atto 3

Safety System

DTC B171E-00 indicates the driver-side knee airbag ignition circuit resistance exceeds the normal threshold range (typically 1.5Ω-3.5Ω, depending on vehicle calibration) established by the SRS control module (ACU), registering as excessively high resistance.

Potential causes include increased internal resistance in the airbag inflator, poor wiring harness connector contact, a wiring harness open or short circuit, or a faulty internal sampling circuit within the control module.

This fault forces the SRS system into a degraded mode and illuminates the instrument panel airbag warning light.

During a collision, the knee airbag may fail to deploy, compromising lower limb protection for the driver.

5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Aging or moisture causes the knee airbag igniter internal resistance to drift out of normal range.
  • 2Airbag wiring harness connector (usually located under the left side of the dashboard, yellow plug): terminals oxidized, loose, backed out, or corroded from water ingress.
  • 3Knee airbag wiring harness worn, broken, or pinched inside the instrument panel, reducing the effective conductive cross-sectional area.
  • 4Liquid ingress into the airbag connector during vehicle wading or interior cleaning causes increased contact resistance.
  • 5SRS control module (ACU) internal resistance sampling circuit fault or abnormal software calibration causing a false alarm.
What To Do
  • 1
    Use the BYD VDS or a dedicated diagnostic tool to read and confirm DTC B171E-00, record freeze frame data, and check the airbag warning light status on the instrument panel.
  • 2
    Disconnect the battery negative terminal and wait at least 3 minutes to completely discharge the SRS system and prevent accidental airbag deployment.
  • 3
    Remove the driver's side dashboard lower trim panel and locate the left knee airbag wiring harness connector (yellow plug, usually with a shorting bar). Inspect the connector for damage, water ingress, oxidation, or burn marks.
  • 4
    Disconnect the airbag connector. Use a digital multimeter to measure the resistance between the two terminals of the knee airbag igniter (standard value: approximately 2.0-3.0 Ω). If the resistance is >3.5 Ω or unstable, the airbag assembly is faulty.
  • 5
    Check wiring harness continuity (between the connector and the ACU). Measure the wiring harness resistance (must be <1Ω) and insulation resistance to ground (must be >1MΩ). Inspect for high resistance or intermittent open circuits.
  • 6
    Check the connector pins for oxidation, backing out, or deformation. If necessary, clean with electrical contact cleaner, repair the pins, or replace the wiring harness.
  • 7
    Reconnect all connectors and confirm the locking tabs are engaged. Reconnect the battery negative terminal. Use the diagnostic tool to clear the fault code and perform the SRS system self-test (KOEO and KOER tests).
  • 8
    Perform a simulated crash sensor test (if supported) and verify the knee airbag circuit status displays 'Normal' and the fault code does not return.
Real-World Cases
BYD DTC AI Analysis

Oxidation on wiring harness connector pins increased contact resistance

✓
A 2017 Qin EV300 with 80,000 km had a constant airbag warning light on the instrument cluster. A scan tool read DTC B171E-00. Removing the trim beneath the driver's side dashboard revealed obvious white oxidation on the internal pins of the yellow knee airbag harness connector. Contact resistance measured 5.2 Ω. We cleaned the pins thoroughly with electronic cleaner, applied conductive paste to prevent further oxidation, and reconnected the connector securely. The resistance returned to 2.1 Ω. After clearing the fault code, the system returned to normal.
BYD DTC AI Analysis

Knee airbag internal igniter resistance drift due to aging

✓
A 2017 Qin 100 with 120,000 km had an intermittent airbag warning light and sporadic DTC B171E-00. Repeated measurements showed the knee airbag resistance fluctuating irregularly between 2.8-4.5Ω, indicating an aging internal igniter causing unstable resistance. Replaced the driver-side knee airbag assembly (part number matched to VIN) after removing the lower dashboard trim panel. After installation, performed SRS system configuration and calibration using VDS. This completely resolved the fault.
BYD DTC AI Analysis

Connector water ingress and corrosion after wading

✓
A 2018 Qin EV450 showed an airbag warning light after driving in heavy rain, storing DTC B171E-00. Inspection found the driver's floor mat damp, obvious water stains inside the knee airbag harness connector, and green corrosion on the copper pins, increasing contact resistance to over 6Ω. Thoroughly cleaned and dried the harness connector, measured airbag resistance normal at 2.0Ω, also checked body seals and drain holes, and repaired the air conditioning intake seal to prevent further water ingress.
BYD DTC AI Analysis

Connector loose after unqualified repair

✓
A 2017 BYD Qin 80. The airbag light came on after the owner replaced the cabin filter. Inspection found the knee airbag connector (located near the cabin filter) hadn't been fully inserted, and its locking tab wasn't engaged, causing poor terminal contact and high resistance. Re-seated the connector until it clicked into place, cleared the DTCs with a scan tool, and the SRS self-test passed. Only qualified technicians should perform airbag repairs.
BYD DTC AI Analysis

SRS control module internal sampling circuit fault

✓
A Qin EV300 repeatedly logged fault code B171E-00 even though the left knee airbag resistance measured 2.1Ω (normal) on multiple tests. Wiring harness continuity and insulation were both good, and connectors showed no faults. Other circuits also triggered intermittent false alarms. Diagnosed as an internal resistance sampling circuit or A/D converter fault in the SRS control module (ACU). Replaced the airbag control module (ensure the replacement part number matches or is compatible with the original). After module coding, VIN writing, and system configuration, the fault was completely resolved.
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.