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How to Test a Crankshaft Position Sensor

Difficulty:
Moderate
Time:
1 hour

Quick answer

Start with codes and cranking RPM. If the scanner shows zero RPM during a no-start, inspect the CKP connector and harness, identify whether the sensor is two-wire magnetic or three-wire Hall effect, then test its supply, ground and signal using the vehicle procedure.

Tools you’ll need

  • OBD-II scanner with live data
  • Digital multimeter
  • Vehicle wiring diagram and service procedure
  • Oscilloscope for definitive intermittent-signal testing, when available

Parts

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Step-by-step

  1. 1 Record codes and cranking RPM

    Save freeze frame and companion camshaft or voltage codes. During the no-start, watch engine RPM. Zero RPM supports a missing crank signal, but still does not distinguish sensor, wiring or reluctor.

  2. 2 Inspect the connector and harness

    Look for oil, water, spread terminals, melted insulation and chafing near rotating parts or the exhaust. Flex the harness while watching live data if the fault is intermittent.

  3. 3 Identify the sensor type

    Use the wiring diagram. A two-wire variable-reluctance sensor generates AC voltage; a three-wire Hall-effect sensor normally has power, ground and a switching signal. Applying the wrong test can misdiagnose or damage the circuit.

  4. 4 Verify supply and ground

    For an active sensor, check the specified supply and ground under the conditions in the service procedure. If either is missing, trace that circuit before replacing the sensor.

  5. 5 Check the signal

    Back-probe as directed and observe the signal during cranking. An oscilloscope best reveals dropouts and damaged reluctor teeth. Meter resistance is only valid when the manufacturer specifies it and does not prove every sensor good.

  6. 6 Inspect installation and perform relearn

    If replacement is justified, inspect the reluctor where visible, preserve the specified air gap and seal, torque the sensor correctly and perform any required crankshaft-position variation relearn.

Related codes

Frequently asked questions

Does zero RPM prove the sensor is bad?
It proves the computer is not seeing a usable crank signal. The sensor, connector, wiring, reluctor or sometimes the control module can be responsible.
Can I test every CKP sensor with resistance?
No. Sensor designs differ, and many active sensors cannot be judged by a generic resistance value.
Why does it fail only when hot?
Heat can open an internal winding or connection. Capturing the signal during the hot failure is more useful than testing after it cools.
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