AU
C050200

This DTC indicates the IPB (Intelligent Integrated Braking System) control unit detects an abnormally low-resistance connection between the left front wheel speed sensor (WSS) power supply circuit (typically a 12V DC supply) and body ground (GND), indicating a short to ground — Seal U

Braking System

This DTC indicates the IPB (Intelligent Integrated Braking System) control unit detects an abnormally low-resistance connection between the left front wheel speed sensor (WSS) power supply circuit (typically a 12V DC supply) and body ground (GND), indicating a short to ground.

The wheel speed sensor uses a two-wire design (multiplexed power/signal or independent power and ground).

When the power supply circuit shorts to ground, the sensor fails to receive normal operating voltage.

This causes a complete loss of the left front wheel speed signal and prevents the IPB from monitoring the left front wheel speed.

This fault directly degrades or completely disables systems including the Anti-lock Braking System (ABS), Electronic Stability Control (ESC), Traction Control System (TCS), Automatic Emergency Braking (AEB), and Electronic Parking Brake (EPB).

The vehicle may enter a safety protection mode (limp mode) and brake pedal feel may change, severely compromising driving safety.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1Damaged insulation on the left front wheel speed sensor wiring harness rubs against metal body components (such as the steering knuckle, lower control arm, or fender liner retaining screws) during suspension travel, causing the power wire to short to ground.
  • 2Internal drive circuit breakdown in the wheel speed sensor body (e.g., shorted Zener diode or filter capacitor), shorting the power supply pin to the housing (ground).
  • 3Wheel speed sensor connector seal failure (seal ring aged or improperly installed) allows water or electrolyte ingress, causing a short circuit between the power pin and ground pin.
  • 4Breakdown of the MOSFET or related protection device in the left front wheel speed sensor power supply drive circuit inside the IPB control unit, causing a short to ground at the output terminal.
  • 5During vehicle modification (such as installing fender liners or sound insulation) or accident repairs, fixing screws crush, clips pinch, or hole edges cut the wiring harness, resulting in insulation damage.
What To Do
  • 1
    Visual inspection: Raise the vehicle and remove the left front wheel. Inspect the wheel speed sensor wiring harness routing near the fender liner, suspension spring seat, steering knuckle, and lower control arm. Check for wear, chafing, crushing, or burn marks. Inspect the connector for looseness, water ingress, corrosion, or backed-out pins.
  • 2
    Voltage measurement: Disconnect the left front wheel speed sensor connector, turn the ignition switch to ON, and measure the voltage between the harness-side power supply pin and ground. Normal voltage is 12V (battery voltage). A voltage of 0V or very low (<1V) indicates a short circuit in the wiring harness or at the IPB end. Normal voltage indicates a possible internal short to ground in the sensor.
  • 3
    Resistance measurement: Turn off the ignition, disconnect the IPB control unit connector (or wheel speed sensor connector), and use a multimeter to measure the resistance between the left front wheel speed sensor power supply circuit and body ground. Normal resistance is greater than 10 MΩ (infinite). If the resistance is less than 1 Ω or the buzzer indicates continuity, confirm a short to ground.
  • 4
    Section-by-section troubleshooting: If testing confirms a harness short circuit, measure section by section (gradually peel back the harness sleeve or disconnect intermediate connectors from the sensor end toward the IPB end) to pinpoint the short circuit location. Focus inspection on the harness where it passes through body openings, retaining clips, moving suspension parts, and the section parallel to the front wheel brake hose.
  • 5
    Component isolation check: If the wiring harness measures normal (infinite resistance to ground), replace the left front wheel speed sensor and test. If the fault persists, reconnect the wiring harness and measure the resistance to ground at the corresponding output pin of the IPB control unit. Continuity indicates an internal short circuit in the IPB. Replace the IPB assembly.
  • 6
    Repair verification: After repairing the wiring harness (re-wrapping with insulating tape, applying heat shrink tubing, or replacing the harness assembly) or replacing components, restore all connections. Use a diagnostic tool to clear the fault code. Perform a wheel speed sensor signal consistency check (read the data stream to confirm the left front wheel speed signal changes synchronously with the right front and rear wheel speeds during driving). Road test the vehicle to confirm the ABS/ESC warning light turns off and the system functions normally.
Real-World Cases
BYD DTC AI Analysis

Song Plus DMi left front wheel speed sensor harness rubbing against suspension causing C050200

✓
While driving on rough roads, the ABS and ESC warning lights occasionally illuminated on the dash, clearing after an ignition cycle. The scanner retrieved DTC C050200, with freeze frame data showing the fault occurred at approximately 30km/h. Raised the vehicle and found the left front wheel speed sensor wiring harness had come loose from its retaining clip near the lower control arm, allowing the harness to rub against the suspension spring seat. Long-term chafing wore through the insulation, exposing the copper strands of the power wire and causing an intermittent short to ground. Repaired the damaged section by re-soldering the wires and insulating with heat shrink tubing. Re-routed and secured the harness, ensuring minimum 20mm clearance from all moving parts. Replaced the cable ties and protective sleeving. Fault eliminated.
BYD DTC AI Analysis

Internal circuit breakdown in the left front wheel speed sensor caused a short to power.

✓
After washing the vehicle, C050200 set immediately at startup and would not clear; the brake system warning light stayed on constantly. Disconnected the left front wheel speed sensor connector and measured 12V at the harness side, confirming normal IPB supply voltage. However, measuring between the sensor body pins and housing showed 0.3Ω between the supply pin and metal housing—an internal short to ground. Replaced the genuine left front wheel speed sensor (part number must match the IPB system version), cleared the fault codes, performed wheel speed sensor static calibration (Steering Angle Sensor and WSS Zero Calibration), and road-tested to confirm the repair. The sensor seal failed, allowing moisture into the internal circuit board and causing the power management chip to fail.
BYD DTC AI Analysis

Left front wheel speed sensor connector short circuit due to water ingress during rainy season

✓
After continuous heavy rain, the dashboard displayed a 'Brake System Fault' warning. Read DTC C050200. Inspection found water and green corrosion inside the left front wheel speed sensor connector, causing the power terminal to short to the ground housing and adjacent signal terminal. The connector seal had deteriorated and was missing, allowing water to splash in while driving through standing water. Cleaned the male and female terminals with electrical contact cleaner, sanded off the oxidation layer, replaced the waterproof seal, and applied insulating silicone grease at the connector mating surface to prevent further water ingress. Repaired the damaged corrugated tubing on the wiring harness to ensure waterproofing. Fault resolved.
BYD DTC AI Analysis

Internal drive circuit fault in IPB integrated brake unit

✓
PDI inspection on a new vehicle revealed DTC C050200; the code would not clear and the vehicle had not been driven. The left front wheel speed sensor harness showed no visible damage. At the sensor connector, the power supply line measured 0 Ω to earth (short circuit). They disconnected the 40-pin connector between the IPB control unit and harness and measured both sides: harness side pin 39 (left front WSS power supply) showed infinite resistance to earth (normal), while pin 39 on the IPB side showed continuity to earth. This indicated an internal short to earth in the IPB left front wheel speed sensor power supply drive circuit, likely from a production batch component defect. They replaced the IPB assembly (Intelligent Power Brake integrated braking unit), bled the system, calibrated the wheel speed sensor and longitudinal acceleration sensor, and cleared the fault.
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.