AU
C003108

This DTC indicates the ABS control unit detects an abnormal or completely lost signal input while monitoring the left front wheel speed sensor — Seal U

Braking System

This DTC indicates the ABS control unit detects an abnormal or completely lost signal input while monitoring the left front wheel speed sensor.

The wheel speed sensor (typically magnetic or Hall-effect) generates a pulse signal by monitoring the rotation of the tone ring on the half shaft or wheel hub.

Systems such as ABS, ESC, and EPB rely on this signal to calculate wheel speed.

The control unit sets C003108 when the signal voltage falls outside the threshold (<0.5V or >4.5V), the signal frequency is abnormal, or intermittent interruptions occur.

This fault prevents accurate detection of the left front wheel speed.

It triggers ABS failure, deactivates the ESC system, disables the automatic emergency braking system, and potentially affects the coordinated control of the energy recovery system.

On pure electric models such as the E5, it also affects motor torque distribution and coasting energy recovery smoothness.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Left front wheel speed sensor failure: Internal coil open circuit (magnetic type resistance should be 1.2-1.6 kΩ) or damaged Hall element, causing no signal output or insufficient output amplitude.
  • 2Abnormal sensor installation gap: Bearing wear, loose sensor retaining bolts, or mounting bracket deformation causes the gap between the sensor and the tone ring to exceed the standard value (0.3-1.2 mm), resulting in signal amplitude attenuation.
  • 3Wiring harness and connector faults: Steering or driving over bumps pulls the chassis wiring harness, causing internal wire breakage (commonly near the fender liner); connector water ingress and oxidation; or shielding layer damage causing electromagnetic interference.
  • 4Reluctor ring fault: Metal filings or mud/sand adhering to the reluctor ring surface (common after wading), reluctor ring deformation (tyre lever damage during tyre repair), missing teeth, or tooth surface corrosion, causing signal waveform distortion.
  • 5Internal ABS control unit fault: Damaged input-stage amplifier circuit or A/D conversion module fault causes the unit to misinterpret normal signals as abnormal (confirm by process of elimination).
What To Do
  • 1
    Initial inspection: Raise the vehicle. Visually inspect the left front wheel speed sensor for damage. Inspect the wiring harness routing for signs of abrasion or crushing. Inspect the connector for looseness, water ingress, or oxidation.
  • 2
    Reluctor ring inspection: Rotate the left front wheel and inspect the reluctor ring for missing teeth, deformation, cracks, or foreign matter. Clean metal filings and oil from the reluctor ring surface. Check the driveshaft bearing for excessive clearance (replace if radial play >0.5 mm).
  • 3
    Circuit continuity test: Disconnect the ABS pump connector and sensor connector. Measure the circuit continuity of the power wire (+12V), signal wire, and ground wire. Resistance should be <1Ω. Measure the wiring harness insulation to ground. Resistance should be >10MΩ.
  • 4
    Sensor resistance/voltage test: Magnetic inductive sensor resistance must measure 1.2-1.6 kΩ (at 20°C). For a Hall sensor with the ignition ON, the supply voltage must measure 12V ± 0.5V, and the signal wire static voltage must measure 2.0-2.5V.
  • 5
    Dynamic signal test: Connect an oscilloscope or a multimeter set to AC voltage. Rotate the wheel. The magnetic induction type must output >100mV AC voltage that increases with wheel speed. The Hall type must output a 0-5V square-wave signal.
  • 6
    Gap measurement and adjustment: Use a feeler gauge to measure the gap between the sensor and the tone ring tooth. Standard gap: 0.3-1.2 mm. If out of specification, check the sensor mounting bolt torque (usually 8-10 N·m), replace the sensor, or adjust the shims.
  • 7
    Component replacement verification: If the above checks are normal, replace the left front wheel speed sensor with a known good part and road test the vehicle. If the fault disappears, confirm sensor failure; if the fault persists, check the ABS pump.
Real-World Cases
BYD DTC AI Analysis

E5 sensor body aging caused intermittent signal loss

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Vehicle: 2019 BYD E5, 80,000 km. Symptoms: ABS light intermittent, especially on rough roads. Diagnostic tool read C003108 (current fault). Diagnosis: Sensor resistance measured 1.3 kΩ at rest but jumped to open circuit when tapping the body. Found dry solder joint on internal coil. Fix: Replaced left front wheel speed sensor (SK-3630100). Cleared codes and road-tested 20 km. ABS function normal.
BYD DTC AI Analysis

Qin Pro wiring harness connectors oxidized and corroded after water ingress

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Vehicle: BYD Qin Pro DM. Fault: Warning light constantly on. Symptoms: ABS and ESC lights illuminated simultaneously after wading through heavy rain. C003108. Diagnosis: Sensor power supply normal. Signal line voltage only 0.3V (abnormal). Removed left front fender inner harness connector; found mud and water residue inside with pins oxidized green. Repair: Cleaned connector with electronic cleaner, applied conductive paste, dried and reinstalled. Wrapped harness connector with waterproof tape and adjusted mounting position to prevent water ingress. Fault cleared.
BYD DTC AI Analysis

Excessive bearing clearance on Song Plus caused abnormal signal

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Vehicle: BYD Song Plus EV, 60,000 km. Symptoms: ESC warning light flashing above 80 km/h. Scanned DTC C003108 (historic). Diagnosis: Raised the vehicle. Rocked the left front wheel and found noticeable radial play in the wheel bearing (approx. 2 mm). Rotated the wheel and observed excessive variation in the gap between the sensor and tone ring. Signal was normal at low speed, but tone ring wobble caused signal loss at high speed. Resolution: Replaced the left front wheel hub bearing assembly (including tone ring). Reinstalled the sensor and adjusted the gap to 0.8 mm. No recurrence.
BYD DTC AI Analysis

Iron filings on E5 tone ring caused signal waveform distortion

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Vehicle: 2018 BYD E5, commercial vehicle. Symptoms: ABS warning light on, DTC C003108. ABS triggers early during braking (false activation). Diagnosis: Sensor and wiring tested normal. Disassembly revealed the reluctor ring coated with heavy brake dust and metallic debris, causing abnormal magnetic flux changes and noisy signal output. Fix: Thoroughly cleaned the reluctor ring surface and blew out the sensor head with compressed air. Inspected brake pads—severely worn, generating excessive dust. Replaced the brake pads. Fault resolved.
BYD DTC AI Analysis

Song Pro wiring harness wear causes intermittent open circuit

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Vehicle: BYD Song Pro, 40,000 km. Symptom: ABS warning light illuminates at full steering lock and extinguishes when straightened. Diagnosis: Repeatedly simulated full left lock. When the fault occurred, the sensor signal line showed infinite resistance to ground. Inspected the harness along the left front shock tower; the harness had stretched at full lock, with internal conductors partially fractured and only a few strands remaining. Resolution: Cut out the damaged section, repaired with soldered same-specification wire, rerouted clear of the steering sweep, and secured to the body bracket. Fault resolved.
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.