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PEX Aftermarket Vehicle Speed Sensors

Purpose and Function:

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Vehicle Speed Sensors (VSS) measure the rotational speed of the wheels, transmission output, or drive shaft and send this data to the ECU and other control systems.

  • Primary uses in heavy-duty vehicles:

    • ABS and traction control systems

    • Cruise control

    • Transmission shift logic and engine load calculation

    • Speed-dependent functions (e.g., retarder, ESC, PTO systems)

  • Accurate speed input is critical for both safety and vehicle performance.

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Features & benefits

  • Real-time wheel or shaft speed detection for ABS, stability, and transmission control.

  • Enhances safety by enabling anti-lock braking and traction systems.

  • Supports fuel-efficient operation by providing precise input for ECU and transmission logic.

  • Rugged design suited to heavy-duty conditions: vibration, dirt, temperature extremes, and fluids.

  • Can be integrated into wheel hubs, transmission output shafts, or differential units for easy maintenance.

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Technical Highlights

  • Sensor types:

    • Passive (variable-reluctance / inductive): Generates AC signal; amplitude proportional to speed.

    • Active (Hall-effect or magnetoresistive): Produces digital square-wave or voltage output; works reliably at zero speed.

  • Placement:

    • Transmission output shaft, wheel hub, or differential housing.

    • Some heavy-duty trucks use multiple sensors (wheel speed + driveshaft) for redundancy and accuracy.

  • Signal characteristics:

    • Passive: AC sine wave; amplitude increases with speed.

    • Active: Digital pulse train or voltage proportional to rotation; used by ECU for precise speed calculations.

  • Output frequency: Proportional to shaft/wheel rpm; frequency input used for cruise control, ABS, and engine control logic.

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Diagnostic and Testing Tips

  • Visual inspection: Check sensor body, wiring, connectors, and tone ring/reluctor for damage or contamination.

  • Static test:

    • Passive sensor: measure coil resistance; ensure it is within OEM spec.

    • Active sensor: verify supply voltage (often 5–12 V).

  • Dynamic test: Rotate wheel or driveshaft while monitoring AC waveform (passive) or digital pulse (active) with a scope or scan tool.

  • Functional check: Compare sensor readings to vehicle speed on dashboard or live scan; discrepancies may indicate sensor or tone ring damage.

  • Replace sensors with intermittent, missing, or erratic signals; check wiring and tone rings first to avoid unnecessary replacement.

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Installation Tips and Common Issues

  • Maintain proper air gap between sensor and tone ring as per OEM specification.

  • Secure wiring away from heat, vibration, and moving parts.

  • Check for tone ring damage (missing/bent teeth or debris) which can mimic sensor failure.

  • Avoid exposure to oils, coolants, or metal debris that can compromise sensor function.

  • After installation, verify signal output and vehicle speed accuracy before finalizing assembly.

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