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B178112

This fault code indicates the SRS (Supplemental Restraint System) ECU detected an abnormally low-resistance connection between the right second-row seat belt pretensioner igniter circuit and the vehicle power supply (12V constant power or ignition switch power) — Seal 6 EV

Safety System

This fault code indicates the SRS (Supplemental Restraint System) ECU detected an abnormally low-resistance connection between the right second-row seat belt pretensioner igniter circuit and the vehicle power supply (12V constant power or ignition switch power).

Under normal conditions, the pretensioner igniter circuit maintains a high-resistance state, consisting only of the 2-3Ω igniter resistance and the wiring harness resistance, and must not have continuity with the power supply line.

A short to power causes the ECU to detect an abnormally high voltage (near battery voltage), triggering the fault code and illuminating the airbag warning lamp.

This fault presents a serious safety risk.

The pretensioner may deploy unintentionally while driving, suddenly tightening the seat belt and injuring the occupant.

Additionally, during an actual collision, circuit protection mechanisms or energy loss through the short circuit may prevent the pretensioner from deploying, failing to protect the occupant.

The B178112 fault code on the Seal 6 EV indicates a high-severity SRS fault where the right second-row seat belt pretensioner igniter circuit may be shorted to 12V power. This can cause unintended pretensioner deployment or prevent it working in a crash. Common causes include damaged wiring in the right B-pillar/floor area or water-corroded connectors. Stop using the seat if possible and visit an authorised dealer. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1Right B-pillar or floor wiring harness insulation wear: Long-term vibration, friction, or seat adjustment damages the insulation on the second-row seat belt pretensioner wiring harness (usually located inside the B-pillar trim or under the seat). The harness contacts a 12V power wire (such as constant power, ignition power, or lighting circuits), causing a short circuit.
  • 2Connector water ingress and corrosion: Vehicle wading, a blocked sunroof drain, or improper car washing causes water ingress at the right middle-row seat belt pretensioner connector (usually located under the seat or at the base of the B-pillar). The resulting electrolytic corrosion between the terminals creates a conductive path, shorting the squib terminal to the power terminal.
  • 3Pretensioner body internal short circuit: The internal bridge wire of the seat belt retractor pretensioner igniter shorts to the housing due to manufacturing defects, aging, or moisture ingress, or leaking igniter compound causes internal conductivity.
  • 4Incorrect wiring or modifications: During vehicle modifications (e.g., installing seat heaters, ambient lighting, or a dash cam), technicians incorrectly tap the power wire into the SRS wiring harness, or the seat slide rail crushes and damages an improperly secured harness.
  • 5SRS control unit internal fault: Breakdown of components such as MOSFETs or capacitors in the ECU internal drive or monitoring circuits causes an internal short circuit between the squib driver terminal and the power supply (relatively rare but requires inspection).
What To Do
  • 1
    Safety preparation: Disconnect the battery negative terminal and wait at least 3 minutes to allow the SRS capacitor to discharge fully. Wear an anti-static wrist strap. Do not measure directly near the airbag system using a standard multimeter resistance setting. Use a dedicated airbag resistor or the diagnostic tool guided function to prevent accidental pretensioner deployment.
  • 2
    Fault confirmation and data recording: Use a dedicated BYD diagnostic tool (VDS or ED400) to read the complete DTC snapshot data. Record the voltage, resistance values, and environmental data present when the fault occurred. Confirm whether B178112 is a current fault (Active) or a history fault (History).
  • 3
    Visual inspection: Remove the right middle-row B-pillar lower trim panel and seat. Inspect the seat belt pretensioner connector (yellow dedicated plug) for looseness, water ingress, corrosion, or burn marks. Inspect the wiring harness corrugated tube for damage or crushing.
  • 4
    Circuit insulation and continuity test: Disconnect the right middle-row pretensioner wiring harness from the SRS ECU connector. Use an insulation resistance tester (megohmmeter, 500V range) to measure the insulation resistance between the pretensioner circuit and the power supply. The normal value is >10 MΩ. Use a multimeter on the voltage setting to check the wiring harness for abnormal voltage to the power supply.
  • 5
    Pretensioner unit test: Replace the pretensioner with a dedicated airbag resistor (2Ω). Check if the fault code changes to an open-circuit fault (e.g., B178111 or high resistance) to determine whether the wiring harness or the pretensioner is faulty. If the fault remains after replacement, the wiring harness or ECU is faulty. If the fault changes, the pretensioner has an internal short circuit.
  • 6
    Detailed wiring harness inspection: Follow the middle-row right floor wiring harness routing (usually along the floor centerline or right door sill). Strip back the corrugated conduit section by section to inspect. Focus on seat mounting bracket edges, wiring harness retaining clips, and body metal contact points. Repair damaged insulation. Replace the wiring harness assembly if necessary.
  • 7
    SRS ECU verification: If the wiring harness and pretensioner are normal, measure continuity between the corresponding SRS ECU pin and the power supply. If the ECU is internally shorted, replace the SRS control unit and perform configuration coding and immobilizer matching.
  • 8
    Repair verification: After repairing or replacing the faulty component, reconnect all connectors and restore battery power. Use the diagnostic tool to clear the fault code. Perform the 'SRS system self-check' or 'Collision Output Test' (Output Test) to confirm B178112 does not return. Finally, perform a road test to confirm the airbag warning lamp turns off and the system has no new fault codes.
Real-World Cases
BYD DTC AI Analysis

Worn right B-pillar wiring harness caused intermittent short circuit

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Vehicle: Qin EV 2019. Customer reported the airbag warning light occasionally comes on, particularly after adjusting the middle row seatback angle. VDS scan showed DTC B178112 (active fault). Removed the right middle row B-pillar trim and found the seatbelt pretensioner harness insulation worn through at the retainer clip below the B-pillar, exposing copper and contacting the constant 12V power wire for the rear door speakers. Seat adjustment pulled the harness, causing intermittent shorts. Repaired the damaged section with heat-shrink tubing, re-routed the wiring to clear moving parts, and relocated the mounting point to increase slack. Fault resolved. No recurrence at 1-month follow-up.
BYD DTC AI Analysis

Connector corrosion after water wading caused the fault

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Vehicle: BYD E2 2019. Water entered the cabin through a blocked sunroof drain tube and flooded the floor. After the workshop drained the water and dried the interior, the owner found the airbag warning light stayed on. The scan tool showed DTC B178112 and multiple seat occupancy sensor faults. Inspection revealed obvious water stains and green copper corrosion inside the right middle-row seatbelt pretensioner connector (located at the lowest point under the seat). An electrolyte conductive path had formed between the igniter terminal and the adjacent power terminal (which supplies the seat heater, optional on this vehicle). Repair: Replaced the pretensioner wiring harness connector (including the waterproof seal), cleaned the ECU-side connector, and treated the pins with dedicated contact cleaner. The pretensioner itself was undamaged, so we did not replace the retractor assembly.
BYD DTC AI Analysis

Internal short circuit in the pretensioner body caused abnormal resistance.

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Vehicle: BYD E3 2020. Accident-repaired vehicle (right rear side collision). Replaced the right second-row seat belt assembly (includes pretensioner). After installation, DTC B178112 appeared and would not clear. Checked new component wiring connections – normal. Measured pretensioner resistance at only 0.5Ω (normal: 2.0–3.0Ω), with 12V to body ground. New part had an internal quality defect: igniter bridge wire shorted to housing. Replaced the pretensioner assembly with a genuine OEM unit (part number must match vehicle configuration; distinguish between versions with and without force limiters). Fault cleared. Use BYD genuine parts when replacing SRS components on accident vehicles. Aftermarket parts risk resistance mismatch or short circuits.
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.