I have a 99 Octavia Turbo Diesel 110, that has an annoying issue at cold start, below 5 degrees the glow plugs are supposed to come on for a period of time and they do not trigger, the light comes on but goes straight off again, the car will start but it struggles.

I had the issue when I bought the car last year, the dealer kept telling me there was no issue with the glow plugs, and eventually changed the temperature sensor witch seemed to fix the issue, it is out of warrantee now and happening again, I know to have a look at the 109 relay to make sure it is not an old one, but is there anything else I should look at, I am not sure which temperature sensor it uses does anyone know? A picture would be great so I can have a look at this.

I guess that would be the coolant sensor on the right hand side of the engine? Should now be a 4 pin green thing, rather than the older ones which were black.

I am at home today so I could take a picture, but it is raining!!

The sensor was about £25 to replace iirc. If you do replace, remember to get a new o-ring seal as well....