Driving on motorway when buzzer sounded and code 4 came up, pulled in and steam comming from under bonnet.Looked it says air conditioning, but wasn’t on anti freeze low on header tank, any one know why 

Sounds like it could be a defective header tank pressure cap.
Replace it and see if that resolves the issue

thanks, had the header tank renewed before but obviously the cap wasn’t. Ordered from Amazon waste of space wouldn’t screw down , got one from gsf no problem went straight on . Thanks for the reply, yet the Amazon one looked exactly the same weird

Yep thats about right for Amazon, they source rubbish from Asia and you get what you pay for really

Can't go wrong with quality parts that cost more but don't need constantly replacing

The part is exactly the same, you’re right it’s the first and last, friend changed the plugs on hi old Range Rover and the smoke coming out was unbelievable. Told me he got them from Amazon + other stuff every thing dumped and renews with quality parts now running sweet as a nut

Hye I bought 2012 merova 1.4, today I felt that coolant is low so I inject 1 litre coolant and when drive about 4 miles my car, code 4 appear and engine is heated on top. What to do please suggest? Even coolant also spilt on the engine when I open and see the engine room.