AU
C003708

C003708 is a UDS-compliant fault code; subtype '08' indicates Signal Invalid/Plausibility Failure — Atto 8

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.

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Cases Logged
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Causes
Likely Causes — Atto 8
  • 1Wheel speed sensor component 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 stuck to the sensor tip alter the magnetic gap.
  • 2Abnormal sensor installation gap: The air gap between the sensor and the reluctor ring is outside the standard range (typically 0.3-1.2 mm). A deformed, loose, or worn mounting bracket causes an excessive or insufficient gap, 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; shielding layer damage 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 oil, dirt, ice, or snow lodged between the teeth, preventing the generation of a regular magnetic reluctance variation signal.
  • 5ABS control unit internal fault: Damaged ECU internal signal acquisition circuit, A/D conversion 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 such as vehicle speed, wheel speed values, and longitudinal acceleration when the fault occurred. Enter live data stream mode. Observe changes in the left rear wheel speed signal while the vehicle is stationary and driving. Check for signal spikes, fixed values, or obvious desynchronization with the other three wheels.
  • 2
    Physical inspection and cleaning: Remove the left rear wheel and inspect the wheel speed sensor head for metal debris, oil contamination, or physical damage; inspect the rear axle tone ring for missing teeth, deformation, or corrosion; clean the sensor head 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 workshop 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
    Harness continuity and signal test: Disconnect the ABS pump assembly connector. 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 generate a regular sine or square wave as the wheel rotates, with amplitude increasing as wheel speed increases).
  • 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 hub unit. Clear the fault code and perform a road test (including straight-line acceleration, deceleration, and turning conditions) to confirm the fault does not return and the ABS function operates normally.
Real-World Cases
BYD DTC AI Analysis

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

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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.

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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.

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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.

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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 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.