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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 — Qin Plus

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 Qin Plus 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, damaged wiring, or an internal fault 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 — Qin Plus
  • 1Knee airbag wiring harness connector loose or disconnected: Water ingress, vehicle modifications, or incomplete seating after repairs can cause poor contact at the dedicated yellow SRS connector located under the instrument panel near the steering column.
  • 2Airbag igniter internal open circuit: Broken or aged igniter coil inside the knee airbag assembly, usually accompanying damage to the airbag module itself. This commonly occurs if the airbag remains unreplaced after an accident or 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 strain the under-dash wiring harness, 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): A fault in the ECU internal detection circuit causes a false open circuit, but this condition typically triggers multiple simultaneous airbag fault codes.
  • 5Clock spring or spiral cable related fault: On some models, the knee airbag wiring harness routes under the steering wheel. An internal open circuit in the clock spring may affect circuit detection (verify the wiring harness routing for the specific model).
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 reading: 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), and record the vehicle status at the time of the fault.
  • 3
    Visual inspection: Remove the driver side lower dashboard trim panel, locate the left knee airbag assembly (inside the dashboard below the steering column), and verify the yellow SRS connector is fully seated. Check that the connector lock is 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 igniter resistance on the airbag side (standard value: 2.0 ± 0.3 Ω). If the resistance is infinite, replace the airbag assembly. Measure continuity on the wiring harness side from the airbag ECU to the connector to check for an open circuit or short to ground.
  • 5
    Insulation and contact inspection: Check connector terminals for oxidation, backed-out pins, or deformation. Measure wiring harness insulation resistance to ground (should be >1 MΩ). Check the SRS ECU connector for looseness.
  • 6
    Component replacement: If diagnostics confirm a faulty airbag assembly, 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. 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. Clear the fault code using the diagnostic tool. Perform the 'SRS system self-check' (typically requires turning the ignition switch to ON and waiting for the system self-check to complete). Verify B17171B does not return and 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 the '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 Qin Plus 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.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.B110BDTC B110B indicates a fault in the internal air pump (sampling pump) of the PM2.5 air quality detector. This pump draws cabin or outside air into the PM2.5 sensor detection chamber, enabling the laser scattering sensor to measure real-time particulate matter concentration. The air conditioning controller (or BCM) sets this DTC upon detecting an open or short circuit in the pump drive circuit, or abnormal current caused by a seized pump motor. This fault disables the "Green Clean" system, causes the instrument cluster air quality display to read abnormally or disappear, and disables the automatic fresh air/recirculation switching function. It does not affect the vehicle powertrain or core thermal management functions.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Qin Plus →Qin Plus 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.