AU
B178812

This DTC indicates a short to vehicle power positive (B+) in the driver-side front airbag Stage 2 inflator circuit — Seal 6 EV

Safety System

This DTC indicates a short to vehicle power positive (B+) in the driver-side front airbag Stage 2 inflator circuit.

In modern dual-stage airbag systems, separate circuits control the Stage 1 and Stage 2 inflators, triggering them in stages based on collision severity (Stage 1 low power, Stage 2 high power).

A short to power means the airbag control unit (ACU) detects the Stage 2 inflator circuit voltage remaining abnormally high (12V).

This prevents this airbag stage from deploying correctly during a collision (because the power supply bypasses the trigger circuit) and creates a major safety hazard of unintended airbag deployment, as the short-circuit current can accidentally trigger the inflator.

The fault may originate in the clock spring, main wiring harness connector, airbag module, or the ACU.

The B178812 fault code on the Seal 6 EV indicates a short to battery positive in the driver-side front airbag Stage 2 inflator circuit. This is a high-severity safety fault because it may stop correct airbag deployment or risk unintended deployment. Common causes include a damaged steering wheel clock spring or worn airbag wiring near the steering column. Visit an authorised dealer for diagnosis and repair. Typical repair cost data is available from recorded cases.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1Damaged or broken insulation on the internal flat wire harness of the steering wheel clock spring (spiral cable) shorts the Stage 2 ignition wire to the power wire. This is the most common cause and often presents with abnormal noise when turning the steering wheel or multifunction button failure.
  • 2Long-term steering friction damages the airbag wiring harness insulation near the steering column, causing it to contact the body power wiring harness (such as the ignition switch power wire) and create a short circuit.
  • 3During front-end accident repairs or interior trim removal/installation, incorrect installation of the airbag wiring harness connector, bent or deformed pins, or screws or cable ties crushing the harness insulation causes a short to power.
  • 4Airbag Control Unit (ACU) internal drive circuit fault (e.g., power transistor breakdown), causing the second-stage drive terminal to short internally to the power supply positive.
  • 5Water ingress from wading or deep interior cleaning corrodes the airbag wiring harness connector (located under the steering wheel or at the main airbag plug), creating a conductive path or copper corrosion bridging the power terminals.
What To Do
  • 1
    Safety preparation: Set the vehicle to OFF. Disconnect the 12V low-voltage battery negative terminal and wait at least 3-5 minutes to fully discharge the SRS backup capacitor. Wear an anti-static wrist strap. Do not use radio equipment near the airbag assembly.
  • 2
    Freeze frame analysis: Connect the VDS or X431 diagnostic tool to read the DTC freeze frame data. Record the vehicle speed, timestamp, and associated fault codes at the time of the fault. Check for accompanying B1788 (Level 1) or other SRS faults.
  • 3
    Visual inspection: Check the clock spring connector under the steering wheel and the main airbag connector (yellow plug) for obvious burning, melting, water ingress, or recessed pins. Check if the airbag wiring harness retaining clips have detached, causing the harness to hang unsupported.
  • 4
    Sectional measurement: Disconnect the connector below the clock spring. Use a multimeter to measure resistance between the stage 2 ignition wire and the positive power supply (normal: infinity/OL). If continuity exists, continue isolating sections to determine if the fault is in the clock spring, body wiring harness, or airbag module.
  • 5
    Component replacement test: If measurements show an internal short circuit in the clock spring, replace the clock spring. If the airbag module has an internal short to power (the airbag connector second-stage pin shows continuity with the housing or power terminal), replace the driver airbag assembly.
  • 6
    Wiring harness repair: If the body wiring harness is damaged, repair it by wrapping two layers of high-temperature insulating tape (neoprene rubber or fibreglass). Avoid ordinary PVC tape (melts at high temperatures). Re-secure the wiring harness to prevent further chafing.
  • 7
    Verification test: Restore all connections and turn on the power. Use the diagnostic tool to clear the fault code and perform the SRS system self-diagnosis (Active Test). Verify B178812 status is 'Past' or cleared. Verify the airbag warning light turns off normally after 6 seconds. Perform a road test to verify.
Real-World Cases
BYD DTC AI Analysis

2019 Qin EV clock spring internal short caused DTC B178812

✓
Airbag warning light stayed on when the vehicle arrived at the shop. Read DTC B178812. Found the code cleared with the steering wheel at full left lock, but returned when centered. Removed the steering wheel and found insulation damage between the stage 2 igniter circuit and power supply wiring inside the clock spring. Replaced the clock spring (part number: BYD-3773110). Fault resolved. Analysis: repeated steering wheel rotation over long-term use caused fatigue damage to the internal wiring.
BYD DTC AI Analysis

E2 ride-hail: Airbag false positive for short-to-power after accident repair

✓
An E2 rideshare vehicle was in a minor frontal collision. After an outside repair shop replaced the front bumper and airbag control unit (ACU), fault code B178812 set and would not clear. Inspection revealed the ACU-to-steering wheel harness retaining clip was missing where the harness passes through the firewall. The harness rubbed against the steering column bracket, wearing through the insulation until the copper core contacted the bracket (ground). The bracket had a high-resistance connection to battery positive through some path. Re-wrapping the harness and fitting a protective sleeve cleared the fault.
BYD DTC AI Analysis

E3: Corroded airbag connectors in flood-damaged vehicle

✓
2020 E3 fault code B178812 appeared one month after flood damage repairs. Found green copper corrosion inside the driver airbag connector (yellow). Electrolyte had formed a conductive path between the second stage ignition terminal and the adjacent power terminal (typically for the horn or multifunction buttons). Cleaned the connector and treated with electronic contact restorer. Insulation resistance returned to normal. Recommend replacing the waterproof airbag connector seal to prevent further water ingress.
BYD DTC AI Analysis

Steering wheel modification damaged the secondary ignition line

✓
A 2019 Qin EV owner fitted a racing steering wheel then reverted to stock, triggering DTC B178812. Inspection revealed that forcible deformation of the shorting bar on the second stage airbag igniter line during disassembly had shifted the pin within the connector into contact with the power pin. Additionally, an incorrect pinout on the aftermarket clock spring used for the modification allowed 12V to enter the airbag circuit. Replacing the clock spring with a genuine unit and repairing the pins resolved the issue.
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.