AU
B178812

This DTC indicates a short to vehicle power positive (B+) in the driver-side front airbag Stage 2 inflator circuit — Atto 8

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 Atto 8 indicates a short to vehicle power in the driver-side front airbag Stage 2 inflator circuit. This is a high-severity safety fault that can stop correct airbag deployment or risk unintended deployment. Common causes include a damaged steering wheel clock spring ribbon cable 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 — Atto 8
  • 1Damaged or broken insulation on the internal flat ribbon cable in 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 occurs 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 collision repairs or interior trim removal and installation, incorrect installation of the airbag wiring harness connector, bent pins, or screws or cable ties crushing the harness insulation causes a short to power.
  • 4Internal drive circuit fault in the airbag control unit (ACU) (e.g., power transistor breakdown), causing an internal short to positive power at the second-stage drive terminal.
  • 5Flooding or deep interior cleaning causes water ingress and corrosion in the airbag wiring harness connector (located under the steering wheel or at the main airbag connector), creating a conductive path or copper corrosion bridging the power terminals.
What To Do
  • 1
    Safety preparation: Switch the vehicle to OFF. Disconnect the 12V low-voltage battery negative terminal and wait at least 3-5 minutes (to ensure the SRS backup capacitor fully discharges). 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 DTCs at the time of the fault. Check for accompanying B1788 (Level 1) or other SRS faults.
  • 3
    Visual inspection: Inspect the clock spring connector under the steering wheel and the main airbag connector (yellow plug) for obvious signs of burning, melting, water ingress, or backed-out pins. Check if the airbag wiring harness retaining clip has detached, causing the harness to hang free.
  • 4
    Sectional measurement: Disconnect the connector below the clock spring and use a multimeter to measure the resistance between the stage 2 ignition wire and the power supply positive (normal reading: infinity/OL). If continuity exists, continue isolating the circuit in sections to determine whether 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 (continuity between the second-stage pin of the airbag connector and the housing or power terminal), replace the driver airbag assembly.
  • 6
    Wiring harness repair: If the body wiring harness is damaged, wrap the damaged section with 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). Confirm the B178812 status is 'Past' or cleared. Confirm 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 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.