What does this thing under the water pump do?

[JBM770]

In the process of changing the water pump I noticed this item didnt have the wiring plugged in and I remembered seeing a plug that wasnt connected to anything near the heater pipes and it fitted.

The engine ran fine without it connected and it didnt seem to affect anything else so I am wondering what it is and what it does.

https://www.aulro.com/afvb/images/imported/2015/02/132.jpg (http://s582.photobucket.com/user/JBM5000/media/IMG_1084.jpg.html)

ps I originally had this at the bottom of my D2 Head Gasket thread without any response so I've created a new thread of its own.

[woko]

Camshaft position sensor

Sent from my GT-I9295 using AULRO mobile app

[PhilipA]

It tells the ECU on what cylinder the engine is for starting.

The Crank sensor can be just past the missing tooth so the engine will not start until the crank sensor passes the missing tooth as the ECU does not know which cylinder to fire.
The cam position sensor gives this info.
You may be lucky and it starts but without it there can be problems starting.
Regards Philip A