AU
C003708

C003708 is a UDS-compliant fault code; subtype '08' indicates Signal Invalid/Plausibility Failure — Atto 3

Braking System

C003708 is a UDS-compliant fault code; subtype '08' indicates Signal Invalid/Plausibility Failure.

In the BYD E5 ABS/ESC system, this fault indicates the ABS ECU detects a persistent abnormality or intermittent interruption in the electrical signal from the left rear wheel speed sensor (RL Wheel Speed Sensor).

Specific conditions include: signal amplitude outside the normal range (too high/too low), distorted signal waveform, excessive deviation from the reference model calculation, or logical inconsistency with the other three wheel speed signals (e.g., the left rear wheel speed reads significantly lower than the others during straight-line driving).

In new energy vehicles, this fault also causes inaccurate torque calculation in the regenerative braking system (RBS), which may restrict regenerative braking functions.

When this fault triggers, the system disables ABS and ESC functions, the ABS/ESC warning lamp illuminates on the instrument cluster, and the vehicle enters conventional hydraulic braking mode.

4
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Wheel speed sensor failure: Aging, open circuits, or short circuits in the internal Hall element or electromagnetic coil cause insufficient output signal amplitude or complete signal loss; metal filings attached to the sensor tip alter the magnetic gap.
  • 2Abnormal sensor installation gap: The air gap between the sensor and the reluctor ring falls outside the standard range (typically 0.3-1.2 mm). Deformed, loose, or worn mounting brackets cause excessive or insufficient gaps, resulting in signal loss.
  • 3Wiring and connector faults: repeated bending of the sensor wiring harness in suspension travel areas (such as the E5 rear suspension-to-body connection) causes internal wire breakage and insulation damage; water ingress into the connector causes oxidation, terminal back-out, or excessive contact resistance; damaged shielding causes electromagnetic interference.
  • 4Tone ring (trigger wheel) defect: The tone ring integrated into the rear wheel hub bearing inner race is deformed, missing teeth, rusted, or has tooth gaps blocked by oil, dirt, ice, or snow, preventing it from generating a regular magnetic reluctance variation signal.
  • 5Internal ABS control unit fault: Damaged ECU internal signal acquisition circuit, A/D converter module fault, or abnormal software calibration parameters (less common; consider only after ruling out preceding factors).
What To Do
  • 1
    Diagnostic tool deep scan: Use VDS or a dedicated diagnostic tool to read the complete fault codes and freeze frame data. Record parameters at the time the fault occurred, such as vehicle speed, wheel speed values, and longitudinal acceleration. Enter live data stream mode. Observe the left rear wheel speed signal while the vehicle is stationary and driving. Check for signal spikes, fixed values, or obvious loss of synchronization compared to the other three wheels.
  • 2
    Physical inspection and cleaning: Remove the left rear wheel. Inspect the wheel speed sensor tip for metal debris, oil contamination, or physical damage. Inspect the rear axle tone ring for missing teeth, deformation, or corrosion. Clean the sensor tip and tone ring surface. Inspect the sensor mounting bracket for looseness or deformation.
  • 3
    Sensor static measurement: Disconnect the sensor connector and use a multimeter to measure the sensor resistance (typically 1.0–1.5 kΩ for E5 models; refer to the repair manual for specific values). An infinite reading indicates an open circuit, and 0 Ω indicates a short circuit. Measure the insulation resistance between the sensor and body ground; the value must be greater than 20 MΩ.
  • 4
    Wiring harness continuity and signal test: Disconnect the ABS pump assembly connector and measure continuity between the sensor harness and the ABS pump (must be less than 1Ω). Check for short circuits to power and ground. Reinstall the sensor, raise the vehicle, and measure the sensor output signal waveform using an oscilloscope (must produce a regular sine or square wave as the wheel rotates; amplitude increases with wheel speed).
  • 5
    Gap adjustment and verification: For adjustable sensors, use a feeler gauge to check the gap between the sensor and the tone ring. If necessary, loosen the retaining bolt and adjust the gap to the standard value (0.3-1.2mm). For integrated sensors with an abnormal gap, check the rear axle bearing housing or replace the wheel hub unit. Clear the fault code and perform a road test (including straight-line acceleration, deceleration, and turning) to confirm the fault does not return and ABS function operates normally.
Real-World Cases
BYD DTC AI Analysis

Worn rear wheel speed sensor wiring harness on E5 taxi caused intermittent fault

✓
2018 BYD E5 taxi, 120,000 km. The instrument cluster intermittently illuminated the ABS warning light. DTC C003708 (left rear wheel speed signal fault) stored; freeze frame showed the fault occurred at 40–60 km/h. Inspection found the left rear wheel speed sensor harness had chafed at the body harness connector near the rear upper control arm. Long-term suspension movement wore the insulation, leaving internal conductors partially broken. The harness lost connection over bumps, triggering the fault. Replaced the left rear wheel speed sensor harness assembly (part number: 10238320-00), rerouted and secured the harness, and added corrugated tubing protection. Fault cleared.
BYD DTC AI Analysis

Iron filings adhered to the left rear wheel speed sensor head, causing abnormal signals.

✓
2019 BYD E5 private vehicle, 30,000 km. ABS warning light constant on. Scan tool shows DTC C003708. Live data: left rear wheel speed signal reads 0 at standstill, spikes momentarily on initial movement, then remains 0. Removed sensor: tip heavily coated with metal powder from brake pad wear, causing magnetic short circuit and blocking tone ring signal. Root cause: owner regularly drives near dusty construction sites without periodic brake system cleaning. Thoroughly cleaned sensor tip and tone ring surface, flushed with carburetor cleaner, reassembled. Signal returned to normal. Advised owner to check wheel speed sensor cleanliness every 20,000 km.
BYD DTC AI Analysis

Rear axle tone ring deformation distorted wheel speed signal waveform.

✓
An E5 with minor rear-end collision damage had the ABS warning lamp come on after repairs, storing DTC C003708. The data stream showed the left rear wheel speed signal fluctuating periodically at stable vehicle speed. Removing the left rear hub unit revealed the tone ring integrated into the wheel bearing had slight elliptical deformation from the impact—barely visible, but showing slight runout when spun. This caused the sensor-to-tone ring air gap to vary cyclically, and signal amplitude fluctuation exceeded the ECU tolerance. Fix: Replaced the left rear hub bearing unit assembly (including the tone ring). Fault cleared. After collision repairs, verify wheel speed signal waveform quality using an oscilloscope rather than just clearing fault codes.
BYD DTC AI Analysis

Loose sensor mounting bracket caused excessive clearance.

✓
BYD E5 2018, 80,000 km. Intermittent ABS warning light with codes C003708 and C003800 (left rear wheel speed sensor power supply fault, intermittent). Found the left rear wheel speed sensor mounting bolt loose; the sensor had backed out, gap to tone ring exceeded 2.5 mm (standard 0.3-1.2 mm). Signal readable at low speed but amplitude dropped at high speed, triggering the ECU signal fault. Sensor wobble also caused intermittent poor contact in the power line, setting the supply fault code. Fix: Torqued the sensor bolt to 8-12 Nm with threadlocker, adjusted sensor to standard gap, and fixed the power terminal contact. Both codes cleared.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For 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.
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.