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[pauldmackay]

Having exactly the same issues as you with this p0420 code!

 I've changed both pre and post lambda's to no avail, ............the pre cat lambda plugs in just behind the top left of the cam cover at the back of the engine, but I believe its the lambda after the cat that causes the emission light to go on.

[pauldmackay]

just to add, the previous owner had the downpipe replaced and there's only 1 cat on mine, so one sensor befor and after, I beginning to believe it just the cat isn't heating up quick enough, if I drive in town for a while and the cars warmed up the light won't come on if I go onto motorways etc, but if I go straight out on fast roads etc from cold, usually guaranteed the light will come in around 8-10 mins, I changed the MAF, plugs, coil pack, temp sensor, fuel filter, air filter etc to no avail! Had the emission checked as not due a mot for a while and all was fine, had the car over to H21 for updates last week and after speaking to him, I'm trying a few tanks of shell V power to see if the light stays off................the lights beginning to get annoying!

[Proz]

just to add, the previous owner had the downpipe replaced and there's only 1 cat on mine, so one sensor befor and after, I beginning to believe it just the cat isn't heating up quick enough, if I drive in town for a while and the cars warmed up the light won't come on if I go onto motorways etc, but if I go straight out on fast roads etc from cold, usually guaranteed the light will come in around 8-10 mins, I changed the MAF, plugs, coil pack, temp sensor, fuel filter, air filter etc to no avail! Had the emission checked as not due a mot for a while and all was fine, had the car over to H21 for updates last week and after speaking to him, I'm trying a few tanks of shell V power to see if the light stays off................the lights beginning to get annoying!

I understand your hatred of this light   .... your discription of when yours comes on is exactly like mine , id never really paid attention that way but now it does sound like mine aswell .... i tried the bp ultimate stuff but sure enough it came on again   ..... so is the only option a new genuine Cat at £800 odds .. i can reset my light when ever it comes on but its still a pain in the a**e  

[Merlindriver]

.. i can reset my light when ever it comes on but its still a pain in the a**e  

How do you reset it?

[pauldmackay]

At the moment I putting it down to the cat not heating up quick enough up enough, I'm no expert on this at all, but as the car orginally would have had pre cat with lambda before and after this and then then main cat with no sensor after that, I would presume that the purpose of the main cat is to clean what the pre cat doesn't.

seen this on ebay for the 2.2 - item 260257204166

From reading many posts the post cat sensor should read rich as their should be no oxygen left, this will only be the case when the cat is up to temperature, the ecu presumes the car should be up to temp after a certain period with sensor inputs etc and if it isn't the emissions light comes on if oxygen is still detected ie the post cat sensor is not reading rich.  If, like mine, there's only 1 cat which will heat up slower as it further away from the engine, it will take longer for the cat work properly.  I'm taking this to be same reason for omegas that have the light coming on but still with orginal 2 cat set up still pass emissions tests as the 2nd cat will do the rest.

Question I've always had is, if the your pre cat is okay and the emissions light is off with the post lambda running rich as there's no o2, whats the 2nd cat doing?

[Proz]

.. i can reset my light when ever it comes on but its still a pain in the a**e  

How do you reset it?

I have a code reader and reset it everytime it comes on which is almost daily  :-/

[Proz]

At the moment I putting it down to the cat not heating up quick enough up enough, I'm no expert on this at all, but as the car orginally would have had pre cat with lambda before and after this and then then main cat with no sensor after that, I would presume that the purpose of the main cat is to clean what the pre cat doesn't.

seen this on ebay for the 2.2 - item 260257204166

From reading many posts the post cat sensor should read rich as their should be no oxygen left, this will only be the case when the cat is up to temperature, the ecu presumes the car should be up to temp after a certain period with sensor inputs etc and if it isn't the emissions light comes on if oxygen is still detected ie the post cat sensor is not reading rich.  If, like mine, there's only 1 cat which will heat up slower as it further away from the engine, it will take longer for the cat work properly.  I'm taking this to be same reason for omegas that have the light coming on but still with orginal 2 cat set up still pass emissions tests as the 2nd cat will do the rest.

Question I've always had is, if the your pre cat is okay and the emissions light is off with the post lambda running rich as there's no o2, whats the 2nd cat doing?

Im actually watching the same item at the moment but cant decide wether to bother if it might or might not work or make any difference  :-/

[pauldmackay]

I know what you mean, other option I suppose could be to remove the warning bulb as a last resort, we've still got the ECU/EML light to report all other faults, not something I would normally do but it might come to that, don't see the point in changing any more parts if its passing MOt emissions test, and many cars don't have this light, I think I'll only change the downpipe/cats if it fails the test.

[Proz]

It would be my last resort ... if i was to change the cat i would get new O2 sensors as well .... if that didnt work it would get a gallon of fuel and a match  

[Proz]

I know what you mean, other option I suppose could be to remove the warning bulb as a last resort

Does it not go into some kind of default / back up fuel map mode if the light is eluminated  :-/ .

[pauldmackay]

I know what you mean, other option I suppose could be to remove the warning bulb as a last resort

Does it not go into some kind of default / back up fuel map mode if the light is eluminated  :-/ .

As far as  I can see post cat sensor that cause that light to go on has no effect on the fueling etc at all, I'm not seeing any difference to fuel economy, performance when it does come on.  It would only go into limp mode if it was running and the ECU/EML light was on if dependign on the code.

Just to let you know though if the emissions light comes on and I reset it, it will stay off for the rest of the day normally.  

[Proz]

I know what you mean, other option I suppose could be to remove the warning bulb as a last resort

Does it not go into some kind of default / back up fuel map mode if the light is eluminated  :-/ .

As far as  I can see post cat sensor that cause that light to go on has no effect on the fueling etc at all, I not seeing any difference to fuel economy, performance when it does come on.  

Just to let you know though if the emissions light comes on and I reset it, it will stay off for the rest of the day normally.  I only use the car usually at the weekend though

Yes i must admit mine isnt quite daily   ... although it does seem to becoming more and more frequent .... 3 or 4 trips to work ( 20 mile round trip ) and she lights up again  

[Entwood]

I have a 3.2 and its not a matter of IF then light comes on for a 0420/0430   .. but WHEn the light comes on ...  

Due to the info from the forum I purchased the restting tools ... but have only had the light on twice in a year .... I do however run on LPG which is somewhat cleaner ..... and might make a difference ..

[Proz]

I should probly just put up with it coming on but i find it very annoying .... i would buy the ebay item and new O2 sensors IF it would cure the problem  ... heard others who have done that and still comes on

[pauldmackay]

Sounds good, the emissions will be that low with the lpg that the cats won't even need to up to normal operating temp to working to be doing enough to keep the light off!

Had a 3.0 elite around 5 years ago with lpg, never has any problems with emission.........it didn't have the annoying emissions light though!