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 — Seal 6 EV

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 Seal 6 EV indicates a high-severity SRS fault where the front passenger second-stage seatbelt pretensioner circuit is shorted to ground. This can disable passenger airbag and pretensioner protection and turn on the SRS warning lamp. Common causes include damaged under-seat wiring or water/corrosion in the pretensioner connector. Visit an authorised dealer to repair wiring or replace the faulty component. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1Worn under-seat wiring harness: During front passenger seat fore/aft adjustment, the pretensioner wiring harness continuously rubs against the metal edge of the seat rail, damaging the insulation and causing a short 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 slide rail) during vehicle wading or carpet cleaning, causing electrolytic conduction between the pins and resulting in a short to ground.
  • 3Wiring harness pinched due to modifications: Retaining clips or screws pierce the pretensioner wiring harness when retrofitting seat ventilation/heating, installing full-coverage floor mats, or fitting seat covers, causing a short to ground.
  • 4Internal short circuit in the pretensioner unit: Insulation failure of the internal bridge wire in the stage 2 pretensioner squib (very rare; usually appears simultaneously with B179C-01 short to power).
  • 5Floor harness chafing against a sharp body edge: Prolonged vibration causes the pretensioner harness routed through the floor to rub against burrs on a body panel hole, 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 move the seat to the rearmost position to gain access for wiring harness 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 slide rail fixing bolts and the floor holes where the harness passes through.
  • 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. The normal value is ∞ (infinite). A reading <10Ω confirms a short to ground.
  • 4
    Segmented isolation diagnosis: Disconnect the pretensioner connector under the seat and measure the resistance to ground on the wiring harness side and the pretensioner side separately. If the wiring harness side has a short circuit, the body wiring harness is faulty. If the pretensioner side has a short circuit, replace the pretensioner assembly.
  • 5
    Wiring harness repair: If a damaged section is found, repair the insulation using a double layer of 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 handling: If the connector has water ingress, 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: If testing confirms 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, clear the fault code using the diagnostic tool, and perform the SRS system self-test. Slide the seat forward and backward while monitoring the B179C-00 status in real time to confirm the fault is completely resolved.
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 Seal 6 EV 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.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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.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 Seal 6 EV →Seal 6 EV 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.