AU
B179C-00

DTC B179C-00 indicates the Airbag Control Unit (ACU) detects an abnormally low-resistance connection (typically <2Ω) between the front passenger side second-stage seatbelt pretensioner firing circuit and body ground — Qin Plus

Safety System

DTC B179C-00 indicates the Airbag Control Unit (ACU) detects an abnormally low-resistance connection (typically <2Ω) between the front passenger side second-stage seatbelt pretensioner firing circuit and body ground.

The second-stage pretensioner is a component of the dual-stage adaptive seatbelt system.

During a severe collision, it triggers sequentially with the first stage to provide progressive restraint protection.

A short to ground causes the ACU to flag this firing circuit as failed, which illuminates the SRS warning lamp, disables the front passenger side airbag and pretensioner functions, and prevents second-stage pretensioner activation during a collision.

This hard fault remains active, and cycling the ignition does not clear it.

Repair the wiring insulation or replace the faulty component.

The B179C-00 fault code on the Qin Plus indicates a high-severity SRS fault: a short to ground in the front passenger second-stage seatbelt pretensioner firing circuit. This can disable the passenger airbag and pretensioner and keep the warning lamp on. Common causes include damaged wiring under the seat or water-corroded connectors. Visit an authorised dealer to inspect wiring/connectors and repair or replace the faulty part. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1Worn wiring harness under the seat: Adjusting the front passenger seat forward and backward causes the pretensioner wiring harness to rub against the metal edge of the seat rail over time, damaging the insulation and shorting to body ground.
  • 2Connector water ingress and corrosion: Water enters the pretensioner connector under the front passenger seat (usually located on the inner side of the seat rail) during vehicle wading or carpet cleaning. This causes electrolyte conduction between the pins, creating a short to ground.
  • 3Pinched wiring harness due to modifications: Retaining clips or screws pierce the pretensioner wiring harness when retrofitting seat ventilation/heating, fitting full-coverage floor mats, or installing seat covers, causing a short to ground.
  • 4Pretensioner unit internal short circuit: Insulation failure of the internal bridge wire in the second-stage pretensioner squib (very rare; usually accompanies B179C-01 Short to Power).
  • 5Floor harness interference with a sharp body edge: The pretensioner harness routed through the floor rubs against burrs on a body sheet metal hole due to long-term vibration, damaging the insulation and contacting the body ground.
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal and wait at least 3 minutes to fully discharge the SRS capacitor. Remove the front passenger seat headrest and adjust the seat to the rearmost position to access the wiring harness for inspection.
  • 2
    Visual inspection: Inspect the pretensioner wiring harness under the seat (typically two wires inside a yellow corrugated conduit) for wear, cuts, or burn marks. Focus on the seat track mounting bolt area and the hole where the harness passes through the floor.
  • 3
    Resistance measurement: Disconnect the airbag control unit (ACU) connector, locate the front passenger second-stage pretensioner circuit pins, and measure the resistance between this circuit and body ground. Normal resistance is ∞ (infinite). A reading <10Ω confirms a short to ground.
  • 4
    Sectional isolation diagnosis: Disconnect the pretensioner connector under the seat. Measure the resistance to ground on both the wiring harness side and the pretensioner side. If the wiring harness side has a short circuit, the fault is in the body wiring harness. If the pretensioner side has a short circuit, replace the pretensioner assembly.
  • 5
    Wiring harness repair: If you find a damaged section, apply double-layer insulation using heat-shrink tubing or electrical tape, and re-secure the wiring harness away from sharp edges; if the damage is severe, replace the floor wiring harness assembly.
  • 6
    Connector treatment: If water ingress is present, clean the pins with electrical contact cleaner, blow dry, apply insulating silicone grease, and check the integrity of the waterproof sealing ring.
  • 7
    Component replacement: Upon confirming a short circuit in the pretensioner body, replace the front passenger seat belt assembly (including the pretensioner). Do not repair the pyrotechnic device separately.
  • 8
    Verification test: Restore all connections, turn on the power, use the diagnostic tool to clear the fault code, and perform the SRS system self-check. Slide the seat forward and backward while monitoring the B179C-00 status in real time to confirm complete fault elimination.
Real-World Cases
BYD DTC AI Analysis

Worn seat tracks cause intermittent short circuit

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Vehicle: Qin EV300 2017. Customer reported the SRS warning light lit intermittently, more often on bumpy roads. Scanner read historic fault B179C-00 (intermittent short to ground). Inspection found the yellow wiring harness corrugated tube beneath the passenger seat contacted the inner metal edge of the seat rail at full rearward travel. Friction wore through the insulation, exposing copper that touched the seat frame and shorted to ground. Repair: Wrapped the damaged section with abrasion-resistant tape, repositioned the harness retaining clips, and verified clearance throughout the seat’s full travel. Cleared codes and cycled the seat rail repeatedly; fault resolved.
BYD DTC AI Analysis

Pretensioner connector corroded and shorted after water ingress

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Model: Qin 100 2017. After wading repairs, the SRS warning light remained on with current DTC B179C-00. Inspection revealed the pre-tensioner connector beneath the front passenger seat (2-pin yellow) had water stains and green copper corrosion inside, with 0.8Ω between pins. Root cause: previous wading depth exceeded the seat rails, and the degraded seal let water in. Cleaned the connector, dried it with compressed air, and applied insulating silicone grease; resistance returned to normal on retest. Advised customer to replace the connector seal and inspect other SRS connectors on the same side to prevent repeat water ingress.
BYD DTC AI Analysis

Aftermarket heated seat installation damaged the wiring harness

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Model: Qin EV450 2018. SRS warning illuminated after the customer had a passenger seat ventilation system installed at an aftermarket shop. Removing the seat revealed the installer had secured the fan with self-tapping screws, penetrating the seat foam and piercing the seatbelt pretensioner harness. This shorted both positive and negative wires to the seat frame (ground), triggering DTC B179C-00. The short burned out the ACU internal protection circuit. Repair: Replaced the damaged harness section (from the floor connector to the pretensioner), repaired the seat foam, and rerouted the wiring to avoid the aftermarket components. Since the ACU locks the fault after detecting a short, we performed an SRS system configuration reset using the diagnostic tool.
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.