AU
C050400

DTC C050400 indicates the IPB (Intelligent Integrated Braking System) control unit detects an "indirect uncertainty" (plausibility fault) in the left front wheel speed sensor signal — Seal 6 EV

Braking System

DTC C050400 indicates the IPB (Intelligent Integrated Braking System) control unit detects an "indirect uncertainty" (plausibility fault) in the left front wheel speed sensor signal.

This is not a simple sensor open or short circuit.

Instead, the control unit algorithm identifies a logical inconsistency between the left front wheel speed signal and the vehicle's actual motion state, the speeds of the other three wheels, and the longitudinal/lateral acceleration sensor data.

Symptoms include signal spikes, an abnormal fixed value (such as a constant 1845 km/h), a signal rate of change exceeding physical limits, or intermittent signal loss within specific vehicle speed ranges (usually >60 km/h).

This fault triggers degraded protection modes in systems including ABS, ESP, and automatic emergency braking, severely affecting vehicle dynamic stability control.

The C050400 fault code on the Seal 6 EV indicates a plausibility fault in the left front wheel speed sensor signal, detected by the IPB braking control unit. Severity is medium, as ABS, ESP, and emergency braking may enter reduced-function modes. Common causes include contamination on the magnetic encoder target wheel or an aging wheel speed sensor. The recommended fix is to 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
  • 1Magnetic encoder target wheel contamination: Iron filings (brake pad wear dust) or oil accumulating on the surface of the half shaft magnetic encoder distort the magnetic field signal, causing an abnormal square-wave signal or signal loss.
  • 2Wheel speed sensor aging: Hall element performance degrades, causing insufficient output signal amplitude. The control unit cannot correctly recognize the signal at high rotational speeds.
  • 3Intermittent wiring harness fault: Left front wheel speed sensor harness experiences intermittent short or open circuits during steering or suspension travel, or oxidized connector pins or backed-out terminals cause increased contact resistance.
  • 4Abnormal installation gap: The air gap between the sensor and the tone wheel exceeds the standard range (0.2-1.2mm) due to collision, bushing wear, or mounting bracket deformation, resulting in insufficient signal strength.
  • 5Electromagnetic interference: High-voltage system (drive motor, DC-DC) interference couples into the wheel speed signal line, or damaged sensor shielding causes signal distortion.
What To Do
  • 1
    Initial diagnosis: Use the VDS diagnostic tool to read the complete fault code freeze frame. Record the vehicle speed and wheel speed data when the fault occurred. Enter "Live Data Stream" mode and observe the four wheel speed signals. Verify if the left front wheel shows 0 km/h, a fixed abnormal value (such as 1845km/h), or differs significantly from the other wheels.
  • 2
    Basic check: Turn off the ignition. Inspect the left front wheel speed sensor connector (usually located near the shock absorber) for looseness, water ingress, or oxidized pins. Measure the sensor resistance (Hall type approx. 1.0-1.5 kΩ, magnetic induction type approx. 0.8-1.4 kΩ). Check the wiring harness for continuity and insulation to ground.
  • 3
    Target wheel inspection (critical step): Raise the vehicle and remove the left front tire. Clean the sensor head. Remove the left front driveshaft and thoroughly inspect the magnetic encoder target wheel surface for metal debris, scratches, or magnetic pole damage. Clean the target wheel with a clean soft cloth and alcohol. Never scrape with metal tools.
  • 4
    Air gap and waveform inspection: Use a feeler gauge to measure the air gap between the sensor and the tone wheel (standard: 0.2-1.2 mm). If available, use an oscilloscope to measure the sensor output signal waveform. A normal signal is a 0V/12V square wave (Hall type) or sine wave (magnetic inductive type). Inspect for missing waveforms, noise, or abnormal amplitude.
  • 5
    Dynamic verification: Clear the fault code and road test the vehicle, focusing on speeds above 60 km/h and steering maneuvers. If the fault is intermittent, simulate suspension movement (raise the vehicle, engage a gear to rotate the wheels, and simultaneously shake the wiring harness) to check for intermittent poor contact. If the fault persists, replace the wheel speed sensor with a genuine part and recalibrate (some models require sensor calibration).
Real-World Cases
BYD DTC AI Analysis

Song PLUS DM-i ABS light on during high-speed driving; wheel speed signal stuck at 1845km/h

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Symptoms: Engine and ABS warning lights illuminated intermittently while driving, readily reproduced above 60 km/h. Once triggered, the left front wheel speed signal froze at 1845km/h. Diagnosis: Scan tool retrieved P121B00 (Left Front Wheel Speed Sensor Signal Abnormal) from CEMS and C050400 (Left Front Wheel Speed Sensor Signal Fault) from IPB. Disconnected the sensor connector and inspected the ABS plug pins; no abnormalities. Replaced the sensor but the fault persisted. Removed the driveshaft and found the magnetic encoder ring coated in iron filings. Solution: Cleaned the iron filings from the encoder ring, reinstalled the driveshaft, and test drove. Fault eliminated. Key point: You cannot see the internal debris by removing only the wheel speed sensor; you must remove the driveshaft to clean it thoroughly.
Original source ↗
BYD DTC AI Analysis

BYD All-Model Wheel Speed Sensor General Diagnostic Procedure (Official Technical Bulletin)

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Symptoms: Dashboard ABS/ESP warning lights on, ESP function limited, possible abnormal ABS activation while driving. Diagnostic procedure: 1. Used VDS to read ESP/ABS DTCs, confirmed C050400. 2. Checked left front wheel speed sensor harness connections and resistance (normal: 1.0–1.5 kΩ). 3. Checked installation gap (0.2–1.2 mm). 4. Inspected reluctor ring for metal debris, oil, or damage. 5. Used oscilloscope to check wheel speed sensor signal for interruptions or abnormalities. Resolution: Clean or replace left front wheel speed sensor; clean or replace half-shaft magnetic encoder ring; repair wiring harness short/open; replace half-shaft assembly if necessary.
BYD DTC AI Analysis

Song/Qin Series Multi-System Warning (ESP/ABS Fault)

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Symptoms: While driving, the instrument panel suddenly displayed "Check ESP System" and "Check ABS System" warnings, accompanied by multiple system alerts. Diagnosis: Scanned the vehicle using VDS1000 and retrieved C050400 (Left Front Wheel Speed Sensor Signal Fault) from the ESP module. Found slight oxidation on the wheel speed sensor connector. Resistance measured within normal range but voltage signal was unstable. Further inspection revealed abnormal wear marks between the sensor and the tone ring. Resolution: Replaced the left front wheel speed sensor, cleaned the connector and applied conductive grease, and removed oxides from the tone ring surface. Cleared the fault codes and road tested 20 km. Fault did not reappear.
Original source ↗
BYD DTC AI Analysis

Intermittent brake system fault in new energy vehicles (intermittent short circuit in wiring harness)

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Symptoms: BYD Tang/Han models intermittently display "Check Brake System" on the instrument cluster while driving, with ESP function restricted and abnormal vehicle speed signals. Diagnosis: Scanned the ABS/ESP system and retrieved DTC C050400. Data comparison revealed intermittent fluctuations in the left front wheel speed signal. Raised the vehicle and found the left front wheel speed sensor harness rubbing against the fender liner at full steering lock; worn insulation caused an intermittent short to ground. Inspection also found metal powder from brake pad wear covering the target wheel surface. Repair: Repaired the damaged harness and rerouted it to avoid interference. Thoroughly cleaned the left front half-shaft magnetic encoder target wheel (removed the half-shaft for cleaning). Replaced the damaged harness protective sleeve.
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.