What does a Crank Sensor Do?

[JohnDotCom]

With my current problems (listed elsewhere) it has been suggested it may even be a problem with with Crank Sensor.

This got me wondering what exactly does this item do on a Diesel Car?

I know people say change the Crank and Cam sensors on poor starting (mine starts fine by the way)
But just interested in its real purpose and duties so to speak.

[Phil]

It provide data to the ecu on position of crankshaft so it knows when to inject fuel.

Normally though a crank sensor either works or it doesn't. I've not ever come across one that is a bit iffy. Maybe one that either works or doesn't but not one that is just a bit funny.
Doesn't mean to say it can't happen though.

Is the engine more rattly than before?

[Greeners]

John

Chapter & verse


Crankshaft Position (CKP) sensor
The CKP sensor is located in the engine block, beneath the starter motor, with its tip adjacent to the outer
circumference of the crankshaft reluctor ring.
The CKP sensor works on the variable reluctance principle. This uses the disturbance of the magnetic field which is
set up around the CKP sensor, caused by the rotation of a reluctor 'target' attached to the crankshaft. The reluctor is
a steel ring with 58 'teeth' and a space where two teeth are 'missing'. The teeth, and spaces between, each represent
3° of crankshaft rotation. The two missing teeth provide a reference for angular position. As the reluctor rotates
adjacent to the sensor tip, a sinusoidal voltage waveform is produced which can be interpreted by the ECM into
crankshaft angular position and velocity.
The signal from the CKP sensor is required by the ECM for the following functions:
l To determine fuel injection timing.
l To enable the fuel pump relay circuit (after the priming period).
l To produce an engine speed message for broadcast on the CAN bus for use by other systems.
The two pins on the sensor are both outputs. To protect the integrity of the CKP signal the cable incorporates a
screen. The cable screen earth path is via the ECM. Correct CKP sensor outputs are dependent upon the air gap
between the tip of the CKP sensor and the passing teeth of the reluctor ring. The CKP air gap is not adjustable in this
application.
In the event of a CKP sensor signal failure any of the following symptoms may be observed:
l Engine cranks but fails to start.
l Engine misfires.
l Engine runs roughly or stalls.

[BigRuss]

The crank sensor senses a gap in the reluctor ring on the crank to tell the ECM when the engine is at TDC in the form of a sine wave signal this enables the ECM to calculate the speed and position of the crankshaft.

This signal is used by the ECM to support the fuelling strategy for the engine.
It is also is used by the ECM to calculate engine speed and is sent to other various vehicle systems.

This signal is processed by the ECM to calculate the exact speed and position of the crankshaft so that it can inject the fuel at the correct time.

If this Sensor fails or the signal from it gets corrupted then the engine won't run and won't start until replaced or problem sorted.

Easiest way to tell if crank sensor is o.k. is to watch rev counter , if it works or twitches when cranked over (should the engine not start) then it's usually fine

Russ

[JohnDotCom]

Thanks for your replies Guys.
Very Informative and useful information for the future.,

[Jontie]

Excellent answers guys, well done, but no info on the cam sensor then?

[Greeners]

Originally Posted by Jontie

Excellent answers guys, well done, but no info on the cam sensor then?

Camshaft Position (CMP) sensor
The CMP sensor is located on top of the engine on the camshaft cover. This sensor is a Hall effect sensor producing
one pulse for every camshaft revolution. The CMP sensor is only used on start up to synchronise the ECM programme
with the CKP signal. This is to identify number one cylinder for correct injection timing. Once this has been achieved
the input from the CMP sensor is no longer used in any of the ECM strategies.
Electrical input to the CMP sensor is supplied via the main relay located in engine compartment fuse box. One output
is sensor earth, the other is the signal output to the ECM.
In the event of a CMP sensor signal failure the engine will crank but will not start.

[JohnDotCom]

Originally Posted by Jontie

Excellent answers guys, well done, but no info on the cam sensor then?

Thats more because I didn't ask for that Info in OP.
But Greeners to the Rescue. Thanks.

[Jontie]

Brilliant !!! Most impressed !! We're all up late tonight then???

Good night, I'm off to bed!

[Greeners]

Originally Posted by Jontie

Brilliant !!! Most impressed !! We're all up late tonight then???

Good night, I'm off to bed!

Some of us are stuck at work...