P0420

[Billathome65]

Yep it's a bank 1 code just came up on the car I just bought off the daughter for £500.

Now I know the car has just had the timing belt replaced so am assuming that the head gasket was replaced to as the valves got bashed. Added to this it did have some oil contamination in the coolant before the belt went that is no longer present after a system flush.

With that in mind I'm going to put a possible cat failure to the back of the line at the moment and thinking it may be a 02 sensor that has become contaminated?

Which 02 sensor would be the most likely to have been affected by possible antifreeze the one at the start and easiest one to get to or the 2nd one?

Also if it has been contaminated Or is suspected can it be cleaned and replaced to retest or should it be discarded I asking as if it's the 2nd option then its a trip to the garage to find out which one is failing or if it's the cat.

Cheers Billy boy

[Billathome65]

I take it no one has any advice on this issue? I stuck my U581 scanner on the car to get some live data but strangely I am told that there is no live data stream I was under the impression that this scanner works on all European cars of this age it worked perfectly on my old Renault and an old Corsa any insight????

Bill

[Paul-R]

I can't work out what car you're talking about here. It might be help if you tell us and what engine it has.

[Mandrake]

You might find this helpful:



ScannerDanners diagnostic videos are top notch (he teaches engine diagnostics for a living) and this one specifically covers P0420.

As Paul said above, knowing what car and engine you have would help a lot too.

[Billathome65]

Sorry guys OK an update

I have the car in my cars thing with my user name so assumed incorrectly that you guys would know again I apologize It's a Citroen C3 LX 1.4i 2002.

To start, cheers for the link I do watch a lot of SD's videos he is as you say top notch I saw this video but as I don't have such sophisticated scanners I was still left wondering if it was the cat or sensor.

I popped over to Eric the car guys channel ( I know not everyone's cup of tea ) however he is a good friend of SD's I believe and they appear to have a mutual respect.

Anyway ETCG showed how to check for a bad cat using a hand held scanner with live dater and showed how using the o2S1 02S2 readings you could identify a bad cat. I used this method and sure enough the same scenario played out on my scanner I quantified my readings using a car with a good cat and sure enough it was as he described.

I have been to the scrappy and bought a cat from a 07 C3 allegedly with a sensor I checked the Ohmage with a multi-meter and I get a reading of 0.81 so that's working and saves me having to fork out for a sensor socket

I'm assuming the cat will need a new gasket at the manifold? will I also need some sort of gasket or paste where it connects to the exhaust?

I'm a little worried about the bolts snapping so will drench them with WD40 hows best to remove should I go tight then loose.

Cheers for any advice.

ETCG Video



Bill

[Hell Razor5543]

If you can get hold of it Plus Gas is far better at unseizing bolts. It has the tag "dismantling fluid" on the cans, and it does work a lot better than WD40. Ideally you would spray it on daily for a week or so, and then you should find the bolts come undone almost as if they had only just been done up.

[chinkostu]

I'm guessing it has the cat in the manifold? if so, use shedloads of plusgas and get it nice and warm, i've snapped a couple in my time before thinking this. you can easily drill the stubs out and use a bolt + nut though, likewise the first part of the manifold usually comes off easily.

gaskets should be easily available at your local parts shop i'm pretty sure (i'll have a look in a mo) that theres a firering on the fitting between the centrepipe and the cat that should be replaced just as a matter of course!

[Mandrake]

Glad the videos helped out - yes I've watched a lot of ETCG's videos too...

If you think it is indeed the cat that is faulty then its pretty important to find out why it failed, otherwise it could happen again.

Cats don't generally fail by themselves (unless they are under-spec'ed after market types) but typically fail due to either running rich for a long time or a misfire.

In the case of running rich this might happen if the upstream oxygen sensor was faulty, so double check that is working correctly first. It might also be due to a bad MAP/MAF sensor.

In the case of a misfire an ignition misfire such as a faulty coil over plug can lead to the entire quantity of fuel injected in that cylinder passing straight through into the exhaust and this will overheat the cat. On some cars it might only be necessary to drive the car moderately hard for a few hundred miles (or less!) to totally destroy the cat through overheating if there is a misfire.

Of course its possible (likely) that the car had either a rich running or misfire fault in the past that lead to the cat being damaged, and that the original faults have subsequently been fixed by the owner but the cat remains damaged.

If it were me I would check carefully that the engine is running well and there is no possibility that it is down on power due to a misfire or that it is running rich before I fitted the new cat. They have been known to fail again very quickly if the original causing fault is not rectified first.

[chinkostu]

Good point there Si, the VTR had a knackered coilpack so would misfire whenever it got damp. as you can imagine that's what killed the cat in the end!

[Billathome65]

Hi funny you should mention the Coil pack as that has just been replaced due to failure and the eml has only come on after then. Going off the ETCG video it certainly looks like the Cat was damaged so have already grabbed a reclaimed one which only cost £20 so if this dies it's not a big loss. The car has also done nearly 100K so an old Cat.

Am going to source some plus gas thanks for the heads up on that guys

will check back once Ive done the change over. What part would I need for the cat to centre pipe?

Bill

[chinkostu]

It's a simple fire ring, you usually buy the whole kit which includes new bolts and springs to clamp it with incase you have to cut the old ones off. probably less than £20 for the lot!


similar to this

[Mandrake]

If the car was driven any distance with a failed coil pack, especially if a heavy throttle was used to compensate for it being down on power it would quite likely destroy the cat through overheating, yes.

It must have been running like a dog if it was misfiring that badly though, if the owner continued to drive the car in that state then they got what was coming unfortunately.

[Billathome65]

Cheers

I will get a kit soon along with a new manifold gasket.

This car is a bit of an enigma, When my daughter bought the car originally i'd overlooked checking the coolant as the Oil filler cap was clean no gunk to suggest water contamination NOPE she had oil contamination in the coolant

I believe also before she bought it the car had traveled to Portsmouth or Plymouth from Manchester and back so think that's classed as a distance

Before she got round to having the head gasket done the timing belt went however there was no indication of any issues before that went apart from the car stalling once or twice I believe.

Obviously the head gasket was replaced at the same time due to having the valves replaced too.

Again with the coil one minute she was driving the car the next it wouldn't start. ( I had listened to the car after the belt was done and told her I could hear a misfire, but she was adamant that all was OK and the miss was a figment of my imagination and wouldn't listen so I wasn't arguing with her )

As I was in bed ( I work nights ) she got the garage out again they diagnosed the coil failure and replaced it. ( he did tell her to wait and let me do it she wanted it done there and then )

Now it's the CAT so no indications normally of issues before the coil died it was running fine. Same as the belt! I just think it's this car.

The one saving grace with this car is untill my daughter bought the car it had been serviced every year.

Bill

[Mandrake]

You didn't mention that it had had a failed head gasket as well!

Catalytic converters are also extremely sensitive to even small quantities of silicone, to the point that you're not allowed to use silicone based greases or sealants on sumps, fuel lines or air intake ducting, or anywhere else that might cause the silicone to be burnt in the combustion chamber and exhausted into the cat.

Guess what most modern coolants have in them ? Yep, silicone... So its actually very common for a head gasket failure which allows coolant into the combustion chamber to destroy a catalytic converter if the car continues to be driven with the failed head gasket...

Unlike a misfire which causes overheating (and potential meltdown) of the cat's ceramic honeycomb due to having excess fuel available for the cat to catalyse, silicone (and some other materials such as lead) causes "poisoning" of the metallic surfaces (palladium etc) which reduces their catalysing efficiency, potentially right down to the point where they don't work at all.

So between a failed coil pack and a head gasket failure this cat didn't stand a chance!

[Billathome65]

I'm sure I mentioned a blown head gasket in another post LOL come on I can't keep saying It had a blown head gasket LOL