2006 Honda Civic Honda Civic Trouble

Engine Mechanical problem
2006 Honda Civic Two Wheel Drive Manual 76053 miles

Hi
I have a Honda Civic 2.2 cdti 2006 (New Shape) and for the last month every now and then I am getting a warning light come up on my dash board along with my glow plug light flashing. In the book it says it is the emmisions or oil sensor and if you turn the engine on/off in 30 second intervals it goes off, when it is happening and I stop, my fan is kicking in as if the car is over heating but my temperature gauge is normal.
When I last filled my car with oil I did overfill it a little but not by much and I just thought that it was that causing the problem but as a few weeks has passed now my oil level is now back below my car still has this problem.

I would be very gratefull if you could help
Thank You for your time
Stuart Sparkes