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 8

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 8 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 functions. Common causes include damaged under-seat wiring from seat movement or water/corrosion in the pretensioner connector. Visit an authorised dealer to inspect wiring/connectors and repair insulation or replace faulty parts. Typical repair cost data is available.
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Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Worn under-seat wiring harness: During front passenger seat fore/aft adjustment, prolonged friction between the pretensioner wiring harness and the seat track metal edge damages the insulation, causing a short to body ground.
  • 2Connector water ingress and corrosion: Water enters the front passenger seat pretensioner connector under the seat (usually on the inner side of the seat rail) during vehicle wading or carpet cleaning, causing electrolyte conduction between the pins and creating a short to ground.
  • 3Harness pinched during modifications: When retrofitting seat ventilation/heating, installing full-coverage floor mats, or fitting seat covers, retaining clips or screws pierce the pretensioner wiring harness and cause a short to ground.
  • 4Internal short circuit in the pretensioner unit: Insulation failure of the internal bridge wire in the second-stage pretensioner squib (very rare; usually occurs simultaneously with B179C-01 Short to Power).
  • 5Floor harness interferes with sharp body edge: The pretensioner harness routed through the floor rubs against burrs on a body panel hole during prolonged vibration. This friction damages the insulation, 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: Check the pretensioner wiring harness under the seat (usually a two-wire harness wrapped in yellow corrugated conduit) for wear, cuts, or burn marks. Focus on the seat slide rail mounting bolt area and the floor opening 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
    Sectional 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 fault is in the body wiring harness. If the pretensioner side has a short circuit, 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 treatment: 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: 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: Reconnect all connectors, turn the power on, use the diagnostic tool to clear the fault code, and perform an 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

✓
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

✓
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 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.