AU
C003408

DTC C003408 indicates the ABS control unit detects an abnormal right front wheel speed sensor (WSS) signal, specifically signal amplitude out of range, signal interruption, or excessive signal noise — Seal U

Braking System

DTC C003408 indicates the ABS control unit detects an abnormal right front wheel speed sensor (WSS) signal, specifically signal amplitude out of range, signal interruption, or excessive signal noise.

On models such as the BYD E5, this sensor typically features a magnetic induction (passive inductive) design, generating a sine wave signal via the alternating magnetic field produced by the rotating tone ring (target wheel).

If the signal voltage drops below the threshold (typically <0.1V), experiences interruption, or exhibits waveform distortion, the ABS/ESC system cannot accurately calculate the right front wheel angular speed.

This disables anti-lock control, Electronic Brakeforce Distribution (EBD), the Traction Control System (TCS), and the energy recuperation braking coordination strategy.

This classifies as a hard fault or an intermittent signal fault.

The instrument cluster illuminates the ABS/ESC warning light, and some models limit energy recuperation strength and switch to a conventional hydraulic braking priority mode.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Open or short circuit in the right front wheel speed sensor internal coil, or aging and failure of the Hall element (if Hall-type), resulting in insufficient output signal amplitude.
  • 2Sensor wiring harness open circuit, short to ground, or short to power; or connector (usually located inside the right front fender liner or below the A-pillar) has oxidized terminals, backed-out pins, or poor contact.
  • 3Sensor target wheel (tone ring) deformation, cracks, missing teeth, or heavy buildup of ferromagnetic debris (such as brake dust or metal shavings) on the surface, causing abnormal changes in magnetic reluctance.
  • 4Right front wheel hub bearing wear creates axial/radial play, causing the air gap between the sensor and tone ring to exceed the standard range (0.3-1.2mm), resulting in a weak or unstable signal.
  • 5ABS control unit internal signal processing circuit fault (uncommon), or deformed right front suspension components (lower control arm, steering knuckle) shifting the sensor mounting position.
What To Do
  • 1
    Initial visual inspection: Raise the vehicle. Inspect the right front wheel speed sensor connector for looseness, water ingress, oxidation, or corrosion. Check the wiring harness at the fender liner and suspension control arm for wear or crush marks.
  • 2
    Sensor static inspection: Disconnect the connector. Use a multimeter to measure the sensor resistance (standard value for magnetic induction type: approx. 1.0-1.6 kΩ at 20°C). Measure the insulation resistance between the pins and to ground (must be >10 MΩ). Replace the sensor if the resistance is infinite or zero.
  • 3
    Dynamic signal test: Connect an oscilloscope or diagnostic tool to read the data stream. Rotate the right front wheel and check for a continuous sine wave or square wave signal output. Verify the signal amplitude changes linearly with wheel speed to rule out an intermittent open circuit.
  • 4
    Tone ring and mechanical inspection: Remove the sensor. Inspect the tone ring surface for scratches, missing teeth, deformation, or attached foreign objects. Use a feeler gauge to measure the air gap between the sensor mounting hole and the tone ring. Inspect the wheel hub bearing for obvious play.
  • 5
    Wiring continuity check: Disconnect the ABS pump connector and sensor connector. Measure wiring harness continuity (should be <1Ω). Measure signal wire insulation to ground and power. Wiggle the wiring harness while measuring to check for intermittent poor connections.
  • 6
    Replacement and matching: After replacing the sensor or repairing the wiring harness, clear the fault code. On some models, use VDS1000/VDS2000 to calibrate the wheel speed sensor or initialize the ESC system. Finally, perform a road test to verify the repair.
  • 7
    Verification and monitoring: During a road test, use the diagnostic tool to read the real-time data stream for all four wheel speeds. Confirm the right front wheel speed changes synchronously with the other wheel speeds, without jumps or loss of synchronization. Confirm the ABS/ESC warning light is off and the system functions normally.
Real-World Cases
BYD DTC AI Analysis

Worn wiring harness on BYD E5 right front wheel speed sensor causing intermittent signal loss

✓
Symptoms: ABS/ESC warning lights intermittently illuminated on rough roads. Fault code C003408 (current/historical). Diagnosis: Lifted the vehicle. Found the right front wheel speed sensor wiring harness chafing against the suspension arm near the steering knuckle. Damaged insulation caused intermittent short between signal wire and shield. Static resistance read normal, but fluctuated when moving the harness. Resolution: Repaired the wiring harness (re-wrapped and re-routed to clear moving parts) and replaced the damaged sensor connector. Fault resolved.
Original source ↗
BYD DTC AI Analysis

BYD Song Multi-System Fault Troubleshooting (Poor Wiring Connection Reference Case)

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Symptoms: While driving, the instrument cluster suddenly displayed multiple warnings: "Check Engine System", "ABS System", "Network", and "Braking System". Diagnosis: VDS scan showed the ESP module reporting CAN data errors. Continuity testing found an open circuit between the GJB06/BJG06 connectors, isolated to a break between pin 16 of AJB01 and pin 27 of WA01(A). Although this case primarily involved the accelerator pedal wiring, the troubleshooting approach for poor contact—measuring connector continuity and checking for backed-out pins—parallels that for wheel speed sensor faults. Solution: Replaced the engine wiring harness (including related connectors). This restored communication and cleared all system faults.
Original source ↗
BYD DTC AI Analysis

Backed-out sensor connector pin caused signal fault in BYD Han EV

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Symptoms: Instrument cluster displayed brake system warning light. Scan tool retrieved wheel speed DTCs (C0034 series). Diagnosis: Right front wheel speed sensor connector had backed-out terminals, causing high contact resistance and signal interruption. Harness continuity measured unstable resistance. Resolution: Reseated terminals to proper position and confirmed locking tabs engaged. Remeasured harness continuity: <0.5Ω. Cleared DTCs and road tested. Wheel speed signal returned to normal.
Original source ↗
BYD DTC AI Analysis

Deformed tone ring on right front wheel of E5 caused abnormal signal waveform

✓
Symptoms: ABS activates prematurely during braking (pedal kickback). No warning light on the dash, but history code C003408 stored. Diagnosis: Checked the right front wheel speed sensor signal with a scope. Found significant dropouts and amplitude spikes in the waveform. Disassembly revealed the tone ring was locally deformed from a previous bottom-out impact, with bent teeth. Solution: Replaced the right front hub bearing assembly (includes tone ring), cleaned the sensor magnetic tip, and measured the air gap at 0.8mm after installation (within spec). Road test confirmed normal ABS operation.
BYD DTC AI Analysis

Right front wheel speed sensor connector oxidised and shorted after water ingress

✓
Symptoms: After driving through water, the ABS warning light remained on with DTC C003408 stored. Diagnosis: Inspection found internal water in the right front wheel speed sensor connector. The pins showed green oxidation, dropping resistance between the signal wire and ground to approximately 200Ω. Resolution: Cleaned the connector thoroughly with electronic contact cleaner, dried it, then applied conductive grease and waterproof sealant. If oxidation is severe, replace the connector or sensor assembly. Check the wiring harness seal integrity.
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.