AU
B171C-00

DTC B171C-00 indicates the driver's knee airbag circuit resistance is 0 Ω, representing a hard short — Seal U

Safety System

DTC B171C-00 indicates the driver's knee airbag circuit resistance is 0 Ω, representing a hard short.

In the SRS (Supplemental Restraint System), normal airbag squib resistance is 2.0-3.0 Ω.

A 0 Ω reading indicates a line short to ground between the SRS ECU and the knee airbag, an internal short in the airbag squib, or a short caused by abnormal connector terminal contact.

This fault triggers the SRS fail-safe mode.

The airbag may fail to deploy during a collision, or in extreme cases, the wiring fault could cause unintended deployment (a low-probability theoretical risk).

Because the knee airbag sits in front of the driver's knees (beneath the dashboard), water ingress, physical impacts, or aftermarket modifications easily affect this area.

Consequently, it is one of the SRS components most prone to short circuits.

The B171C-00 fault code on the Seal U indicates a hard short in the driver’s knee airbag circuit, with resistance reading 0 Ω instead of the normal 2.0–3.0 Ω. Severity is medium because the SRS may not deploy correctly. Common causes include a loose or corroded yellow knee airbag connector, water ingress, or an internal igniter short. 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 knee airbag connector (yellow plug), backed-out terminals, or water ingress corrosion causing a short circuit between terminals or a short to ground. Commonly occurs after vehicle wading or improper cabin cleaning.
  • 2Internal short circuit failure of the knee airbag igniter (inflator). This internal component fault usually accompanies airbag assembly aging or previous external impact (such as a forceful knee strike).
  • 3Damaged wiring harness insulation causing a short to ground, especially under the steering column or near the instrument panel frame, where vibration and friction cause harness wear and contact with the vehicle body metal.
  • 4Internal SRS ECU detection circuit fault causing incorrect circuit resistance measurement. This rare condition usually sets multiple unrelated airbag fault codes simultaneously.
  • 5Improper procedures during vehicle modifications (such as installing a dash cam or footwell lights) where screws pierce the wiring harness or metal brackets pinch the wiring harness, causing a short circuit.
What To Do
  • 1
    Safety preparation: Switch the vehicle OFF, disconnect the 12V battery negative terminal, and wait at least 3 minutes to fully discharge the SRS capacitor and prevent accidental airbag deployment.
  • 2
    Locate component: Remove the driver-side lower dashboard trim panel (knee bolster) and locate the left knee airbag module (usually below the steering column) and the yellow 2-pin connector.
  • 3
    Initial inspection: Check the connector for looseness, backed-out pins, water ingress, or corrosion. Check the wiring harness for wear or crush marks, paying special attention to interference points with the steering column and instrument panel frame.
  • 4
    Resistance measurement: Disconnect the knee airbag connector. Use a multimeter to measure the resistance on the airbag side (should be 2-3 Ω). If 0 Ω, replace the airbag assembly. Measure the resistance to ground on the wiring harness side (ECU side). If 0 Ω, the wiring harness is shorted to ground.
  • 5
    Wiring harness repair: If the wiring harness is damaged, wrap it with insulating tape or replace it. Securely fasten the wiring harness, avoid interference with metal components, and keep it clear of sharp edges.
  • 6
    Component replacement: If replacing the knee airbag, use genuine parts (verify the part number matches). During installation, fully engage the connector locking tab and listen for a 'click' to confirm locking.
  • 7
    System reset: Reconnect the battery, set the vehicle to ON, and use the diagnostic tool to clear the fault code. Perform 'SRS System Self-check' or 'Configuration and Settings', and confirm B171C-00 does not recur and the airbag warning lamp turns off.
  • 8
    Road test verification: Perform a rough road test to confirm no intermittent faults. Verify the SRS system has no current fault codes (Current DTC).
Real-World Cases
BYD DTC AI Analysis

Loose connector caused a short circuit.

✓
Symptom: The airbag warning light on the dashboard stayed on constantly. A diagnostic scan retrieved DTC B171C-00. The vehicle had no accident history and the fault appeared suddenly. Diagnosis: Per the workshop manual, B171C-00 indicates zero resistance in the driver's knee airbag circuit. The technician removed the driver-side knee bolster and inspected the knee airbag connector, finding the yellow airbag plug loose with poor pin contact causing the abnormal resistance reading. He measured the airbag harness with a multimeter; the resistance read 0Ω (normal 2-3Ω). Fix: Disconnected the negative battery terminal and waited 3 minutes. Reseated the knee airbag connector firmly, ensuring the locking tab clicked into place. Cleared the DTC and powered on the ignition for self-test; the fault code cleared and the warning light went out.
Original source ↗
BYD DTC AI Analysis

Internal short circuit in knee airbag.

✓
Symptoms: During routine service, a technician found a stored DTC B171C-00 in the airbag system that could not be cleared. The vehicle had no collision history but had undergone interior trim modifications. Diagnosis: The technician first checked the wiring harness connectors and found no faults; disconnected the airbag connector and measured resistance directly across the airbag unit pins, finding 0Ω (normal is approximately 2–3Ω). This indicated an internal squib short circuit in the knee airbag or an internal fault within the airbag module. Resolution: Replaced the left knee airbag assembly (part number to be confirmed according to specific model). Reconnected the component, used a scan tool to perform 'Configuration and Setup' programming, cleared the DTCs, and the system returned to normal.
Original source ↗
BYD DTC AI Analysis

Wiring harness chafed through, shorting to ground

✓
Symptoms: The airbag warning lamp illuminates intermittently when driving on rough roads. DTC B171C-00 (current fault) present. The fault is intermittent and vibration-related. Diagnosis: The technician inspected the knee airbag connector and found it normal. When tracing the wiring harness to the SRS ECU, the technician found the left knee airbag harness chafing against a metal bracket near the steering column. The worn insulation caused a short to earth. Measured resistance to earth: 0Ω. Solution: Repaired the damaged wiring (wrapped with insulation tape or replaced that section), rerouted and secured the harness to prevent interference with metal components. Cleared the DTC and road tested to confirm the fault was resolved.
Original source ↗
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.