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P codepowertrainMedium severity

P0528Fan Speed Sensor Circuit No Signal

The engine computer sees no signal at all from the cooling fan speed sensor when the fan should be turning.

Definition

The PCM expects a pulsed signal from the fan speed sensor any time the engine is running, since even a disengaged viscous fan windmills at some minimum speed. P0528 sets when that signal is completely absent, meaning the sensor circuit is dead or the fan itself is not rotating. The PCM typically forces the fan clutch to full engagement as a fail-safe (constant fan roar) and turns on the MIL; if the fan is genuinely not spinning, the engine can overheat quickly at idle or under load.

Common causes

  • Open in the signal wire between the sensor and PCM
  • Failed fan speed sensor
  • Disconnected or damaged fan clutch connector
  • Loss of sensor supply voltage or ground
  • Seized or failed fan clutch so the fan is not rotating
  • PCM input circuit fault (rare)

Common misdiagnoses

  • Fan clutch replaced when only the connector or wiring is at fault
  • Thermostat
  • Water pump
  • Coolant temperature sensor
  • Fan relay on systems that have no relay for the viscous fan

Troubleshooting steps

  1. 1.Confirm the fan is spinning

    With the engine running, visually verify the fan rotates; a seized clutch or sheared hub makes this a mechanical problem, not electrical.

  2. 2.Check the connector first

    Inspect the fan clutch connector for being unplugged, melted, or full of corrosion — the harness sits close to exhaust heat.

  3. 3.Verify supply and ground at the sensor

    Key on, confirm reference voltage and a ground drop under 0.1V at the sensor connector per the wiring diagram.

  4. 4.Test the signal circuit for continuity

    With the harness disconnected at both ends, ohm the signal wire from sensor connector to PCM connector; more than a few ohms or an open confirms harness damage.

  5. 5.Scope for output

    With power and ground verified and the fan turning, no square-wave output means the sensor has failed; replace the sensor or integrated clutch assembly.

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