C003700 - C003700 Left Rear Wheel Speed Sensor Signal Fault

Fault Depth Definition

C003700 Left Rear Wheel Speed Sensor Signal Fault represents a critical data link interruption within the Intelligent Power Braking System. In the vehicle chassis dynamics control network, this fault code indicates an abnormality in the wheel speed feedback loop of the left rear axle. As the sensing terminal of the actuator, the left rear wheel speed sensor is responsible for collecting the physical rotational speed and angle information of the wheels in real time and converting it into high-frequency pulse electrical signals transmitted to the central control unit. Once the signal is distorted or interrupted, the system cannot accurately calculate instantaneous vehicle speed or judge wheel slip rate, thereby causing the Anti-lock Braking System (ABS) and Electronic Stability Program (ESP) to lose active intervention capability on the left rear wheel, triggering fault code C003700 to enter safety protection mode.

Common Fault Symptoms

According to current diagnostic data, the following driving experience and instrument panel feedback abnormalities occur after this fault occurs:

• System Function Degradation: Partial function failure of the intelligent power braking system may manifest as adjustment of braking force distribution logic to a non-optimal state.
• Dashboard Warning Lights: The body dynamic stability or anti-lock braking warning indicator light on the dashboard remains constantly illuminated.
• Driving Stability Alerts: The Electronic Stability Program may automatically exit working mode and output fault prompt messages on the display screen.
• Powertrain Perception Abnormality: Under specific conditions, drivers may feel signal logic conflicts between drive wheel speed and vehicle speed data.

Core Fault Cause Analysis

Based on original diagnostic parameters, the root causes of the fault are analyzed in the following three dimensions:

• Hardware Components (Signal Source End): The left rear wheel speed sensor body fails. This usually refers to internal coil open circuit, decreased magnet sensitivity of the sensor head, or abnormality in the signal processing chip, resulting in inability to generate effective output waveforms.
• Mechanical & Physical Environment (Connection End): Excessive dirt accumulation on the left rear wheel hub bearing or damage to the left rear wheel hub bearing ring gear. Dirt accumulation in the bearing area forms magnetic interference objects that hinder normal magnetic field penetration; physical damage to the ring gear (such as broken teeth, foreign object jamming) causes periodic interruption or distortion of the pulse frequency read by the sensor.
• Control & Logic Operation (Decision End): Although data does not directly specify, fault judgment relies on the control unit (ECU/ABS Module) analysis of signal timing. If external interference is too large and calculation results overflow threshold, it will also be recorded as a signal fault.

Technical Monitoring & Trigger Logic

Regarding the judging mechanism for this fault code, the system follows a strict real-time monitoring process:

• Monitoring Targets: The control unit continuously monitors the pulse frequency and signal voltage level characteristics of the output from the left rear wheel speed sensor to ensure it complies with preset dynamic response curves.
• Trigger Conditions: The prerequisite necessary condition for fault judgment is the ignition switch in the ON position. When the vehicle power system is powered on and the diagnostic channel is activated, the ECU starts initial self-check of the wheel speed feedback loop.
• Judgment Logic: During or after the ignition switch is in the ON position, if the left rear wheel rotational speed data received by the control unit is missing, zero value fluctuation, or waveform characteristics are inconsistent with ring gear rotation logic, the system will immediately store fault code C003700 and mark the relevant system entering partial function failure status.