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 U

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 U 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 keep the SRS warning light on. Common causes include damaged under-seat wiring or water/corrosion in the pretensioner connector. Visit an authorised dealer to inspect wiring and connectors, repair insulation, or replace faulty parts. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Worn under-seat wiring harness: During front passenger seat fore/aft adjustment, the pretensioner wiring harness rubs against the metal edge of the seat track over time, 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 creating a short to ground.
  • 3Harness pinched during modification: When retrofitting seat ventilation/heating, fitting full-coverage floor mats, or installing seat covers, retaining clips or screws pierce the pretensioner harness, causing a short to ground.
  • 4Pretensioner unit internal short circuit: Insulation failure of the stage 2 pretensioner squib internal bridge wire (very rare, typically occurs simultaneously with B179C-01 Short to Power).
  • 5Floor wiring harness interference with sharp body edge: Long-term vibration causes the pretensioner wiring harness routed through the floor to rub against burrs on a body sheet metal hole. The friction damages the insulation layer, causing the harness to contact 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.
  • 2
    Visual inspection: Inspect the pretensioner wiring harness under the seat (usually two wires wrapped in yellow corrugated tubing) for wear, cuts, or burn marks. Focus on the seat track mounting bolt area and the harness routing hole in 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 value is ∞ (infinite). A reading <10Ω confirms a short to ground.
  • 4
    Segmented isolation diagnosis: Disconnect the pretensioner connector under the seat. Measure the resistance to ground on the wiring harness side and the pretensioner side separately. If the wiring harness side is shorted to ground, the fault is in the body wiring harness. If the pretensioner side is shorted to ground, replace the pretensioner assembly.
  • 5
    Wiring harness repair: If a damaged section is found, repair it with 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 handling: If the connector has water ingress, clean the pins with electronic contact cleaner. Blow dry, then 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, use the diagnostic tool to clear the fault code, and perform the SRS system self-test. 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

✓
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

✓
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 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.