I got a P0420 code and took my car to have a service and an investigate. I was told my car failed an emissions test and that is likely because the O2 sensors have failed causing a rich mix and higher CO from the exhaust.

But, I have a bit of blue smoke coming out the exhaust when I accelerate hard. I'm planning on doing a compression test to figure out whether it is the valve stems or the piston rings but just wondered, how quickly a new O2 sensor will last in an engine that is burning oil?

I'm planning on getting rid of the car early next year and it's only worth £500-600 so I don't want to spend a load of money fixing it. It just needs to pass an MOT.

It's a 2007 Citroen C1 1.0 Petrol 97k miles.

Also, is there any half decent oil additives to help alleviate oil burning through valve seals or piston rings for just a few months.

Thanks in advance.

  • I don't know about the MOT, but here, visible smoke is an automatic failure during inspection. There are a few products which are supposed to help, but I've not had great luck with them. Your symptoms point to the oil control rings. Unfortunately a compression test won't show you you anything for this. Generally: smoke on acceleration=rings; smoke on deceleration=valve seals. – Pᴀᴜʟsᴛᴇʀ2 Oct 21 '16 at 21:41

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