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[arthill]

Live readings from o2 sensors showed pre cat normal but post cat varying this shouldn't be so I'm told, fault code P0420 is this a faulty cat or could lambda be at fault. any ideas please.

 John

[Kevin Wood]

This code is cat efficiency as thrown ad nauseum on 3.2 engines. 2.2 has the same setup of a small pre-cat followed by a downstream Lambda sensor and the main cat AFAIK.

More likely to be the pre-cat not working properly than the lambda sensor but the chances are the main cat cleans up the emissions to MOT standard anyway, so no desperate need to do anything expensive unless it fails an MOT.

Might be worth running some cataclean through it to try and wake up the pre-cat and stop the light coming on.

Kevin

[arthill]

Thnks Kev I'll try that tomorrow, I recently had problem with MAF when this was there precat sensor was playing up I dont know if there is a connection.
  
  John

[Kevin Wood]

MAF and the pre-cat sensor are both instrumental in getting the mixture right, so if one is telling the ECU lies, it's possible that a code will identify the other as their readings won't match IYSWIM.

The post-cat lambda sensor is just there to verify that the pre-cat is cleaning up the exhaust gas, it doesn't affect engine running, so it will just throw a fault code.

Kevin

[arthill]

thank you

[arthill]

Had car in garage today, tested temperature of cat mechanic told me temp should be approx 30*  hotter post-cat than pre-cat, actual readings showed temp well below what was expected throwing suspicion on cat, I have put cat cleaner through and will test again later. On reading posts on here I thought 2.2 had two cats, only one on mine, If cat needs replaced any suggestions of best supplier and approx cost.  

  John

[arthill]

any comments please

[Marks DTM Calib]

Only one cat?

There should be two, a small pre cat and a big main cat.....unless its a cheap naff after market affair.

[arthill]

That's what I thought but could only see one, thinking about changing downpipe, where's best place to buy?

[Kevin Wood]

I would get the emissions checked. See if you really have a problem.

Kevin

[arthill]

I was thinking that way myself, waiting to see if cat cleaner has helped.