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Crankshaft Rotation Sensor Testing

Modification Details

If your car stalls when it gets up to temperature or refuses to start, your crankshaft rotation sensor could
have failed. You can read all about the faults and how to remove and refit this sensor by clicking here.

The failure of this sensor is well known and people online are very quick to correctly diagnose this fault.

However, there are some cases where the wiring to the sensor is faulty or the replacement sensor is faulty.
This can make it very hard to diagnose. So, we need to check the sensor to see if it's ok.

Coil Test

The crankshaft rotation sensor is a variable reluctance sensor (VRS). These have 2 connections.
They are far more simple than the hall effect sensors that have 3 connections and internal microprocessors.

The VRS only has 2 functioning parts. A copper coil and a permanent magnet.

To test the coil to ensure that the internal copper coil isn't broken (corroded or burnt out)
we need to check the resistance in Ohms between the 2 connector pins.

So, get your multimeter, set it on Ohms and attach the probes to to the sensor connectors.

Keep any metal away from the sensor and take a reading. This reading should be static (not changing).
On this particular sensor (not new), I'm getting a resting resistance of 653Ω (0.653KΩ).

If you get no reading at all, the copper coil has failed and the sensor is junk.

Now try waving a ferrous metal object in front of the sensor. The Ohm reading should fluctuate.

If you get a fluctuation and the reading goes back to the original reading when
you stop waving the metal object, the sensor coil is fine. The variation of the
Ohms is because the coil is picking up the eddy current from the ferrous object.

Reluctance Explanation

Reluctance is a clever thing. The variable reluctance sensor contains a permanent magnet that creates a
directional magnetic field. As the ferrous metal reluctor (a ring with teeth) passes in front of the sensor
it interferes with the magnetic field which in turn affects the resistance of the copper coil.

So, the resistance increases and decreases rapidly as the reluctor passes in front of the sensor.

The car passes 5 volts into the sensor and will monitor the voltage coming back out the other side.

What you get out of the other side is a sine wave. The frequency of the sine wave tells the car how fast the
reluctor is passing in front of the sensor. On the crankshaft sensor set up, it reads teeth spinning around the clutch.

In this position there is a missing tooth to instruct the car of the top dead centre (TDC) position.


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