AU
B179F00

DTC B179F00 indicates a fault in the sensor series circuit of the SRS (Supplemental Restraint System/airbag system) — Seal U

Safety System

DTC B179F00 indicates a fault in the sensor series circuit of the SRS (Supplemental Restraint System/airbag system).

In the BYD Qin PRO, a series or parallel circuit typically connects multiple safety sensors (including the front impact sensor, side impact sensor, and seat occupancy sensor) to the SRS ECU.

The ECU determines sensor status by monitoring the circuit resistance and voltage signals.

The ECU triggers this DTC when it detects abnormal circuit resistance (open circuit, short circuit, or resistance outside the calibrated range of 2.0-4.5kΩ), an incorrect signal sequence, or a communication interruption.

This fault forces the airbag system into a degraded mode.

In extreme cases, it prevents normal airbag deployment during a collision or creates a risk of unintended deployment.

This is a safety-critical fault.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Wear, open circuit, or poor connection in the crash sensor wiring harness inside the front bumper or B-pillar due to chassis scraping or improper accident repair.
  • 2Improper cleaning or liquid spills cause water ingress or pin oxidation at the under-seat occupancy sensor connector, resulting in abnormal circuit resistance.
  • 3Failure to install the sensor or wiring harness to the specified torque after accident repairs causes poor grounding or shielding layer damage, resulting in signal interference.
  • 4Internal SRS ECU detection circuit fault or abnormal software calibration, causing incorrect evaluation of normal circuit resistance.
  • 5Unauthorized modifications (such as installing seat covers or non-genuine seats) compromised the integrity of the sensor series circuit.
What To Do
  • 1
    Use the BYD VDS2000/VDS2100 diagnostic tool to read the complete fault codes and freeze frame data, record the vehicle status when the fault occurred, and check for accompanying fault codes (such as B179E00, B17A000).
  • 2
    Disconnect the battery negative terminal and wait at least 90 seconds to fully discharge the SRS capacitor. Check the instrument panel airbag warning light status.
  • 3
    Visually inspect the front impact sensors (located on both sides of the radiator support) and the side impact sensors (located behind the B-pillar trim panels) for signs of impact or wiring harness damage.
  • 4
    Remove the seat and inspect the seat occupancy sensor (pressure sensor) GJ* series connector (depending on vehicle configuration) for green oxidation, backed-out terminals, or spread pins.
  • 5
    Use a multimeter to measure the total resistance of the sensor series circuit (the standard value is typically the sum of the series sensor resistances; each sensor is approximately 2-3 kΩ). Infinite resistance indicates an open circuit; resistance close to 0 Ω indicates a short circuit.
  • 6
    Use the sectional measurement method: Disconnect intermediate connectors (such as G09 and G10) and measure wiring harness continuity between the sensor and ECU section by section to locate the open or short circuit.
  • 7
    If the wiring harness is normal, replace the suspected sensors one by one (replace the seat occupancy sensor first due to its higher historical failure rate). After each replacement, clear the fault code and perform a system self-diagnosis.
  • 8
    After completing the repair, reconnect all components and the battery. Use the diagnostic tool to perform 'SRS System Configuration' and 'Sensor Calibration' (if applicable). Finally, perform a simulated crash signal test (use a dedicated resistor; never short-circuit directly).
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM front impact sensor wiring harness chafed, causing intermittent open circuit

✓
Vehicle: 2018 BYD Qin PRO DM, 68,000 km. Symptoms: Dashboard airbag warning light illuminates intermittently, with increased frequency on rough roads. VDS scan retrieved DTCs B179F00 (sensor series circuit fault) and B162000 (left front collision sensor fault). Diagnosis: Lifted the vehicle and found the left front collision sensor harness had chafed against the sheet metal edge where it passes through the wheel arch liner. Long-term vibration wore through the insulation and partially severed the copper wires, leaving them intermittently connected. The series circuit resistance read normal at rest but opened intermittently under vibration. Repair: Repaired the damaged harness, protected it with corrugated tubing and rerouted it away from the sharp sheet metal edges. Fault cleared.
BYD DTC AI Analysis

Water ingress caused oxidation in the seat occupancy sensor connector, resulting in circuit resistance drift.

✓
Vehicle: 2019 Qin PRO petrol, 42,000 km. Symptoms: SRS warning light constantly on, DTC B179F00; no collision. Diagnosis: Water stains on the seat base. Owner reported a blocked sunroof drain recently let water into the cabin. Removed the driver's seat and found green corrosion on the occupancy sensor pins (GJ301 connector). The corrosion dropped total resistance in the sensor series circuit from the normal 6.8 kΩ to 2.1 kΩ, below the ECU threshold. Repair: Cleaned the connector with electrical contact cleaner, dried the assembly, replaced damaged harness terminals, and cleared the sunroof drain. Fault resolved.
BYD DTC AI Analysis

After accident repairs, poor grounding of the B-pillar side impact sensor caused signal interference.

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Vehicle: 2018 Qin Pro DM, accident-repaired. Symptom: Right B-pillar impact. After 4S dealership repairs, SRS warning light stayed on and DTC B179F00 would not clear. Diagnosis: Right front seat side impact sensor (GJ302) mounting bolt was not tightened to the 9 N·m spec, causing poor ground between the sensor housing and body. This created noise voltage in the series circuit. Oscilloscope check found abnormal pulse interference on the sensor signal line. Resolution: Sanded the ground point clean to remove paint and oxidation; reinstalled the sensor at 9 N·m with conductive paste; ran SRS system configuration. Fault cleared.
BYD DTC AI Analysis

Aftermarket seat modification caused series circuit interruption

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Vehicle: 2019 Qin Pro petrol variant. Symptom: SRS warning light illuminated the day after the owner fitted aftermarket sport seats. Diagnostic procedure: Retrieved DTC B179F00. Inspection found that during the seat modification, the workshop did not transfer the original seat occupancy sensor to the new seats and simply wrapped the harness terminals with insulating tape. This created an open circuit in the series loop at the seat position. Repair: Installed the OEM occupancy sensor into the new seat cushion (required professional cutting and securing), restored the harness connections, cleared the DTCs with a diagnostic tool, and performed Occupant Classification System Calibration. System returned to normal.
Other Seal U 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.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.
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.