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 — Atto 3

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 Atto 3 indicates a high-severity SRS fault where the airbag control unit detects a short to ground in the front passenger second-stage seatbelt pretensioner firing circuit. This can disable passenger airbag and pretensioner functions. Common causes include worn under-seat wiring or water ingress and corrosion at the pretensioner connector. Visit an authorised dealer to repair wiring insulation or replace the faulty component. Typical repair cost data is available.
3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Under-seat wiring harness wear: 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 front passenger seat pretensioner connector (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.
  • 3Harness compression from modifications: Retaining clips or screws pierce the pretensioner wiring harness and cause a short to ground when retrofitting seat ventilation/heating, installing full-coverage floor mats, or fitting seat covers.
  • 4Pretensioner unit internal short circuit: Stage 2 pretensioner squib internal bridge wire insulation failure (very rare, usually accompanies B179C-01 Short to Power).
  • 5Floor harness interferes with a sharp body edge: Long-term vibration causes the pretensioner harness routed through the floor to rub against burrs on a sheet metal hole, damaging the insulation and contacting 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 conduit) for wear, cuts, or burn marks; focus on the seat track mounting bolt area and where the harness passes through the floor opening.
  • 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. Measure the resistance to ground on the wiring harness side and the pretensioner side separately. If the wiring harness side shows a short circuit, the fault is in the body wiring harness. If the pretensioner side shows a short circuit, replace the pretensioner assembly.
  • 5
    Wiring harness repair: If a damaged point 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 electrical contact cleaner. After blowing dry, apply insulating silicone grease and check the integrity of the waterproof sealing ring.
  • 7
    Component replacement: If the pretensioner body has a short circuit, replace the front passenger seat belt assembly (including the pretensioner). Do not repair the pyrotechnic device separately.
  • 8
    Verification test: Reconnect all connections, turn on the power, clear the fault code using the diagnostic tool, 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 resolution.
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 Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.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.
Common problems reported for Atto 3 →Atto 3 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.