AU
B171C-00

DTC B171C-00 indicates the driver's knee airbag circuit resistance is 0 Ω, representing a hard short — Atto 8

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 Atto 8 indicates the driver’s knee airbag circuit has 0 Ω resistance, meaning a hard short in the SRS wiring or airbag squib. Severity is medium because the airbag may not deploy correctly in a crash. 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.
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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Loose knee airbag connector (yellow plug), backed-out terminal, 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 (generator). This internal component fault typically accompanies airbag assembly aging or previous external impact (such as a forceful knee strike).
  • 3Damaged wiring harness insulation causes a short to ground, especially below the steering column or near the instrument panel frame, where vibration and chafing wear through the harness and cause contact with the vehicle body metal.
  • 4SRS ECU internal detection circuit fault causing incorrect circuit resistance readings. This rare condition typically sets multiple unrelated airbag fault codes simultaneously.
  • 5Improper work during vehicle modifications (such as installing a dash cam or footwell lights) causing a short circuit due to a screw piercing the wiring harness or the wiring harness being pinched between metal brackets.
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). Find 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. Inspect the wiring harness for wear or crushing marks, paying special attention to interference points with the steering column and dashboard frame.
  • 4
    Resistance measurement: Disconnect the knee airbag connector. Use a multimeter to measure the airbag-side resistance (should be 2-3Ω). If 0Ω, replace the airbag assembly. Measure the resistance to ground on the wiring harness side (ECU side). If 0Ω, the wiring harness is shorted to ground.
  • 5
    Wiring harness repair: If the wiring harness is damaged, wrap it with insulating tape or replace the harness. Securely fasten the harness, prevent interference with metal parts, and maintain clearance from sharp edges.
  • 6
    Component replacement: When replacing the knee airbag, use genuine parts (verify part number match). During installation, fully seat the connector locking tab and listen for a 'click' to confirm locking.
  • 7
    System reset: Reconnect the battery, set the vehicle to ON, clear the fault code using the diagnostic tool, perform 'SRS system self-check' or 'Configuration and Settings', and verify B171C-00 does not return and the airbag warning lamp turns off.
  • 8
    Road test verification: Perform a rough road test to confirm no intermittent faults exist, and 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 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.