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 — Seal U

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 Seal U 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 frontal crash. Common causes include a loose or disconnected under-dash SRS connector, damaged wiring, or an internal airbag igniter fault. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Loose or disconnected knee airbag wiring harness connector: Water ingress, vehicle modifications, or failing to fully seat the connector after repairs can cause poor contact at the yellow SRS-specific connector located under the dashboard near the steering column.
  • 2Airbag igniter internal open circuit: The igniter coil inside the knee airbag assembly breaks or degrades, usually coinciding with damage to the airbag module itself. This typically occurs when failing to replace the airbag after an accident 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 wiring harness under the dashboard, breaking the wires; or repeated bending in the sill harness transition area breaks the internal copper strands while the insulation remains intact.
  • 4SRS ECU (airbag control module) internal fault: An internal ECU detection circuit fault causes a false open-circuit report. This condition usually 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: Switch the vehicle 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 when the fault occurred.
  • 3
    Visual inspection: Remove the driver 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 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 airbag-side igniter resistance (standard value: 2.0±0.3Ω). If the resistance is infinite, replace the airbag assembly. Measure continuity on the harness side from the airbag ECU to the connector. Check for an open circuit or short to ground.
  • 5
    Insulation and contact check: Inspect 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 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, reconnect the battery, use the diagnostic tool to clear the fault code, and perform the 'SRS system self-check' (this usually requires turning the ignition switch to the ON position and waiting for the system self-check to complete). Confirm B17171B does not return and verify the instrument panel SRS warning light turns off after the self-check.
  • 8
    Functional test (optional): At an authorised service centre, 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 Seal U Fault Codes
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.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.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.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.B173712DTC B173712 indicates a short to power in the firing circuit of the right second-row side airbag module in the Supplemental Restraint System (SRS). Specifically, the "right second-row side airbag" typically refers to the side impact airbag located in the right B-pillar or the side of the right seat. The "12" suffix indicates a circuit short to battery positive (B+). This fault causes the following conditions: 1) The airbag may fail to ignite and deploy during a collision, resulting in a loss of side impact protection. 2) In extreme cases, unintended triggering may cause accidental airbag deployment. 3) The SRS control unit detects abnormally high circuit voltage (typically above 4.5V) and enters fault protection mode. This may disable the entire airbag system and continuously illuminate the instrument cluster airbag warning light.
Common problems reported for Seal U →Seal U 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.