AU
B171E-00

DTC B171E-00 indicates the driver-side knee airbag ignition circuit resistance exceeds the normal threshold range (typically 1 — Atto 8

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.

The B171E-00 fault code on the Atto 8 indicates high resistance in the driver-side knee airbag ignition circuit. This is a medium-severity SRS fault that can turn on the airbag warning light and may prevent the knee airbag from deploying in a crash. Common causes include a failing igniter or corroded, loose, or damaged wiring/connectors under the dashboard. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Aging or moisture ingress causes the knee airbag igniter internal resistance to drift beyond the normal range.
  • 2Airbag wiring harness connector (usually located under the left side of the dashboard, yellow plug) pins oxidized, loose, backed out, or corroded by water ingress
  • 3Worn, broken, or pinched knee airbag wiring harness inside the instrument panel reduces 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 warning.
What To Do
  • 1
    Use BYD VDS or a dedicated diagnostic tool to read and confirm DTC B171E-00, record freeze frame data, and check the instrument panel airbag warning light status.
  • 2
    Disconnect the 12V battery negative terminal and wait at least 3 minutes for the SRS system to fully discharge to prevent accidental airbag deployment.
  • 3
    Remove the driver's side lower dashboard trim panel, locate the left knee airbag wiring harness connector (yellow plug, usually with a shorting bar), and inspect the exterior 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 the insulation resistance to ground (must be >1MΩ). Check for high resistance or intermittent open circuits.
  • 6
    Check connector pins for oxidation, backing out, or deformation. If necessary, clean with electrical contact cleaner, repair 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). 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 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.