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 8

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.

The B17171B fault code on the Atto 8 indicates an open circuit or high resistance in the driver’s left knee airbag igniter circuit. This is a medium-severity SRS fault because the knee airbag may not deploy in a crash. Common causes include a loose or disconnected yellow SRS connector under the dash or an internal open circuit in the airbag igniter. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Loose or disconnected knee airbag wiring harness connector: Water intrusion, vehicle modifications, or failing to fully seat the connector after repairs can cause poor contact at the dedicated yellow 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 results from failing to replace the airbag after a collision or the airbag exceeding its service life (vehicles over 10 years old).
  • 3Wiring harness physical damage: Pedal operation, floor mat compression, or accident repairs strain the wiring harness under the dashboard, breaking the wire; or repeated bending in the door sill harness transition area breaks the internal copper strands while leaving the insulation intact.
  • 4Internal fault in the SRS ECU (Airbag Control Module): An internal ECU detection circuit fault causes a false open-circuit report. This condition typically triggers multiple airbag fault codes simultaneously.
  • 5Clock spring or spiral cable related fault: On some models, the knee airbag wiring harness passes below 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: Set the vehicle to OFF, disconnect the negative battery 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 when the fault occurred.
  • 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, check that the connector locking tab is fully engaged, and 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 and check for open circuits or shorts to ground.
  • 5
    Insulation and contact inspection: Check the connector terminals for oxidation, backed-out pins, or deformation. Measure the wiring harness insulation resistance to ground (should be >1MΩ). Check the SRS ECU connector for looseness.
  • 6
    Component replacement: If diagnostics confirm a faulty airbag assembly, replace it with an OEM left knee airbag (verify the part number based on the 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, reconnect the battery, and use the diagnostic tool to clear the fault code. Perform the 'SRS system self-check' (usually requires turning the ignition switch to ON and waiting for the system self-check to complete). Verify B17171B does not return and check that the instrument panel SRS warning light turns off after the self-check.
  • 8
    Functional test (optional): At an authorized service center, use the special tool to perform an 'SRS system simulation test'. 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 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.