Code P0420 - Cat or sensors?

GuardianAngel wrote:

GuardianAngel wrote: My list of codes from the workshop manual says for this code "Catalyst system efficiency below threshold"

However, I had a similar code came on if I drove at the same revs for some time and I cleared it and turned the light off, passed an MOT, then the following year, having cleared it a few more times throughout the year it failed the MOT and needed a new CAT to get through.

So I would take MarkyP2000's advice and take it to a friendly MOT station and ask them to put it on their emmissions machine, having turned the light out. If the emmissions are ok, carry on as normal and see what happens.

I don't think putting any cleaning liquid in the fuel will help much really.

I would also advise avoiding Supermarket petrol, especially the big one beggining with T. This kept throwing the equivalent code up on my Mrs BMW 325. The lambda's were tested and are fine, the CAT's apparently never go on those cars and are extremely expensive. It also passed an MOT with very low emmissions. So i suggested to her only buying proper petrol (the Shell 1/2 a mile from the big Supermarket beginning with T price matches them) and it has not come on since!

As a consequence, none of our cars get Supermarket petrol put in them.

As has been said above - do not go to Kwik Fit - you'll find out you need a whole new exhaust, new brake discs and pads, front and rear - despite the fact you have drums on the back, new lambda sensors and windcreen wipers.

Kirkynut

Just before I went on my trip this weekend I put in fuel from T! The light came on during my motorway run, so it was during a long run at highish revs. Interesting parallel.

I will reset the code and get it tested at KwikFit and just ignore their BS about what "needs" to be replaced.

Cheers

Sent from my GT-I9100 using Tapatalk 2

Sorry missed this in my last reply as I was typing it when you posted.

It is interesting about that brand of petrol - when my light kept coming on I had been using their fuel pretty much soley but did not see the link and with the new cat the problem went away. The issue with the Beemer was causing me stress though - fortunately we have the support of an ex BMW man who really knows his stuff - hence no new cats were fitted as he refused to do so knowing they were not the issue but could not put his finger on what might be wrong. I have updated him about the fuel issue so he knows if it rears it's head again with another customer of his.

As long as you know to ignore some of the Kwik Fit advice when you know about cars, all is good.

I once got stung by another well known franchise like them who I believe used a syringe or something to squirt brake fluid under the dust seals of my rear wheel cylinders and got me for new rear cylinders and shoes. I was young and had no knowledge then put was put right by my normal mechanic who had checked them not long before and was annoyed when I told him of the work they had done.

Now I have knowlege about cars I hear the same from others and wince. Proving it when they have disposed of the parts is impossible though.

Kirkynut

markyp2000 wrote:

kirkynut wrote: Yes, a different MOT tester was telling me this recently - is this because there are no published specs for it Mark? So it has to fall back to those stats? That's what I've recently been told. A bit like the Mk1 Eunos Roadster I understand, Mazda never produced specs for that either - am I right?

With the new cat the emmisions did improve dramatically - however, I was somewhat confused by the EML not coming on and staying on, even after I cleared it, to tell me the emissions were out of range.

This could be the reason why - the range the emmissions are allowed to go to are alot higher than it was being tested to!

I have an MOT tester singing from the right song sheet now - so should be alright from now on!

Kirkynut

you dont have to tell me that as i am an mot tester

I know you are, I wasn't telling you, I was asking you if I am right in what I'm thinking, hence the questions ending with a question mark, Mark!

I guess you read it quickly eh?

Kirkynut