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B178E12

DTC B178E12 indicates a short to power (B+) in the front passenger-side second-stage frontal airbag (PAB Stage 2) ignition circuit — Seal 6 EV

Safety System

DTC B178E12 indicates a short to power (B+) in the front passenger-side second-stage frontal airbag (PAB Stage 2) ignition circuit.

The BYD SRS system uses a dual-stage airbag ignition design: the first stage provides a low-energy trigger, and the second stage provides a high-energy trigger for varying collision severities.

This DTC indicates an abnormal electrical connection to the vehicle power circuit within the wiring harness between the SRS control module and the front passenger airbag second-stage inflator (resistance below threshold, typically <2Ω).

This short circuit may cause: 1) unintended airbag deployment (extremely dangerous); 2) airbag deployment failure during a collision (due to bypassed current); 3) the SRS system to enter protection mode, disabling all airbag functions.

The BYD diagnostic protocol identifies the fault suffix '12' as 'Short to Battery+'.

The B178E12 fault code on the Seal 6 EV indicates a high-severity short to battery power in the front passenger second-stage airbag ignition circuit. This can affect airbag operation and may be dangerous. Common causes include damaged or chafed airbag wiring behind the dashboard or A-pillar, or corrosion/water ingress at the passenger airbag connector. Stop using DIY checks and visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Seal 6 EV
  • 1Front passenger airbag wiring harness insulation wear: Vibration, chafing, or improper assembly inside the dashboard, behind the A-pillar trim, or in the floor wiring channel damages the harness outer sheath, causing a short circuit to a power wire (such as constant 12V+).
  • 2Airbag connector water ingress or corrosion: A poorly sealed front passenger airbag connector (usually located behind the dashboard or glovebox) allows electrolytic corrosion to create a conductive path between terminals after water wading, exposure to high humidity, or an A/C condensate leak.
  • 3Clock spring internal short circuit: On vehicles equipped with an integrated clock spring, damaged insulation between the internal flat cable layers shorts the airbag ignition circuit to the horn/multifunction switch power supply wire.
  • 4SRS control module internal driver circuit fault: Internal breakdown of the airbag driver chip (such as a dedicated NXP or Infineon IC) or false detection by the ignition loop monitoring circuit, resulting in a false short-to-power signal.
  • 5Incorrect wiring after accident repairs: After replacing the instrument panel, center console, or front wiring harness, technicians mistakenly connect the airbag wiring harness in parallel with permanent live circuits, such as the instrument illumination or cigarette lighter power supply.
What To Do
  • 1
    Safety Preparation and Diagnostic Confirmation: Use the BYD VDS or Launch X431 diagnostic tool to read all fault codes. Confirm B178E12 is a current fault (not a history fault) and record freeze frame data (including vehicle speed, collision signal status, etc.). Disconnect the 12V battery negative terminal and wait at least 3 minutes to fully discharge the SRS capacitor.
  • 2
    Wiring harness visual inspection: Remove the passenger-side lower dashboard trim panel, glove box, and lower A-pillar trim panel. Inspect the airbag wiring harness (usually wrapped in yellow corrugated conduit) for wear, crushing, or burn marks. Focus on the contact points between the wiring harness and the dashboard metal bracket, A/C duct, and sharp body edges.
  • 3
    Connector inspection: Disconnect the front passenger airbag module connector (located behind the dashboard; remove retaining bolts) and the SRS control module connector (usually located in the center tunnel or under the center console). Check the terminals for water ingress, green corrosion, and deformed pins. Clean with compressed air and apply a dedicated electronic contact protectant.
  • 4
    Circuit measurement verification: At the SRS module connector, use a multimeter set to resistance to measure the resistance between the second-stage airbag ignition wires (usually marked PAB Stage 2+ and PAB Stage 2-) and the vehicle power supply (B+). The normal reading is infinite (OL). A reading <10kΩ indicates a short circuit. Test the circuit in sections to locate the short (clock spring, intermediate harness connector, or airbag module itself).
  • 5
    Component replacement test: If the wiring harness is normal, replace the original airbag module with a known-good front passenger airbag simulator (resistance 2Ω±0.5Ω). Clear the fault code and power on for a self-check. If the fault disappears, replace the airbag module. If the fault remains, replace the SRS control module or repair the wiring harness.
  • 6
    System verification and calibration: After repair, reconnect all connectors and the battery. Use the diagnostic tool to perform 'SRS system self-diagnosis' and 'configuration reset' (write the VIN if replacing the control module). Verify the fault code clears and does not recur, and verify the airbag warning light turns off after 6 seconds.
Real-World Cases
BYD DTC AI Analysis

Qin EV passenger-side airbag harness corroded and shorted after water ingress

✓
2019 Qin EV. Owner reported the airbag warning light stayed on after the vehicle drove through water. DTC B178E12 (current fault) present. Removed the passenger glovebox and found water in the airbag connector; terminals were oxidised green. Further inspection showed the AC drain hose was blocked, causing condensate to drip onto the airbag harness connector below the blower motor. Cleaned the terminals with electronic contact cleaner, replaced the connector seal, and cleared the AC drain hose. Fault resolved.
BYD DTC AI Analysis

E2 aftermarket navigation installation caused airbag harness misconnection to power

✓
A 2020 BYD E2 airbag warning light illuminated the day after an aftermarket head unit installation at a third-party workshop. Diagnostics revealed DTCs B178E12 and B178D12 (passenger airbag first stage short to power). Inspection found the installer had mistaken the passenger airbag wiring harness (yellow connector) for the original radio constant power wire, splicing it into the 12V supply. Technicians corrected the wiring connections, repaired the damaged insulation on the airbag harness, and reset the SRS module configuration.
BYD DTC AI Analysis

E3 clock spring internal inter-layer short circuit

✓
A 2020 BYD E3 had an intermittent airbag warning light when turning the steering wheel to specific angles. Scanned code B178E12 (intermittent). Checked the passenger airbag harness with no issues found. Found the integrated clock spring under the steering wheel had an internal flat cable with an interlayer short; turning the wheel caused the airbag circuit to intermittently short to the horn power supply. Replaced the clock spring assembly. Fault resolved.
BYD DTC AI Analysis

SRS module internal fault after accident repair

✓
A 2019 Qin EV showed an airbag fault on the instrument cluster after front collision repairs (front bumper and condenser replaced; airbags did not deploy). The scan tool read DTC B178E12, which would not clear. The passenger airbag harness measured infinite resistance to power; the harness was normal. The fault persisted with an airbag simulator. The SRS control module had sustained impact damage during the collision, damaging the internal second-stage ignition drive circuit. Replaced the SRS control module and completed online programming and matching; fault resolved.
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.