Hey, first post \o/

So, my 2003 1.6 petrol focus fail its MOT because of hight CO.

Bit of bac ground on the car.. Bout the car about 8 months ago and the guy was telling me it had a new exsaused (it looked new) and everything looked good about the car so I bought it for the boss.

A few days last the engine warning light came on so I took it to my local garage and he plugged it in. The guy told me it was the front (or first?) O2 censor. He had a look and said its not been changed and that I would need it changing.

Anyway I didn't get it done because the wife didn't have time with us both working and yesterday it had its MOT and failed. The same guy said changing the o2 censor would fix it?

Anyway they were fully booked and so I took it elsewhere and that garage said it would be the CAT.

So anyone any idea what it could be?

Another thing I forgot to mention is that after a few months the exsause started rattling at low revs but stopped after a few weeks. A friend and the first garage said it was some part inside the back box and I would need a new back box but the noise stopped so I never bothered.

Sorry for the wall of text on my first post but I don't want to be wasting chas when it's this close to Christmas :-)

Thanks for any advice

Try changing the O2 sensor first, as you have been advised, as that should be cheaper & quicker than replacing the cat ( if it's faulty )

Google translate is a wonderful thing . . . :)

The guy at the second garage has said the CO emissions won't be high because of a failed sencor so that's why he thinks its the CAT.

I don't know anything about cars as you can probably tell.

What sort of price will it be for a CAT?

Google translate is a wonderful thing . . . :)

Google translate is a wonderful thing . . . :)

Is my writing that bad? :-)

In a word - yep ! :)

You need the codes that the garage found on the diagnostic machine to identify the issue, or it's guesswork really

I'll try find out the codes. He just plugged in the snap-on computer and said it was the front o2 censor. He then turned it off but it came back on.

If his machine identified a code that identified it's the O2 sensor - then it probably is :)

But would that then cause high emissions? Just got me wondering with a different garage saying something else.

Yes it can, as it can cause an abnormal air / fuel ratio resulting in the engine running lean or rich - resulting in poor emissions

I'll get that changed then. Thanks for the help!

No worries :)

was it just the co high? what were the hc reading and lambda readings, you can tell alot from those readings, if the lambda passed then the hego sensor is working ok.

check the mot emmision sheet you got with the mot fail and post what readings you had .

That's the sheet. Scaned it with a app on my phone. Well impressed :-D

well done. the lambda reading on both fast idle tests shows the hego sensor to be working ok, if the sensor was faulty then the air fuel ratio would be outside the range, infact the 2nd fast idle shows a perfect 1.0 , the hc is within limits but higher than normal.

co and hc are reduced by the cat

the rattle you mentioned could be the cat breaking up and bits blowing down exhaust.the rattle can stop when the honeycomb in the cat wedges up inside, but this can then allow gasses around cat therefore increasing co/hc

im not saying this is the case with yours , its just my opinion without seeing car.

the garage should be checking the downstream hego sensor with an occiliscope for the wave form , this can see if the cat is working efficiently or not and upstream hego for rich lean switching

so basically my opinion is cat.

Now we have some hard info I agree with Ian :)

Well that's a bit annoying. Just ordered a o2 sencor. Might as well change that anyway.

The exsause is only a year old. The was a recipt with the car but I'm not sure if it was the full thing or now.

How much will a CAT set me back? Just wondering if its worth fixing because its getting old now and not worth much as it is.

The wife knows how to drive now (first car) so I don't mind getting something a bit newer anyway.

Thanks for the replys

Just a quick update.

I changed the o2 censor today. (Part was already ordered) and the warning light is still on. IF it is that that's the problem with the light go off over time or will I need the warning turning off and see if it comes back on?

Have you got something to cancel the fault code?

Incidentally, my focus has the o2 sensor problem, but I deleted the fault code myself. Will the engine have now changed it mixture, possibly causing high emissions to fail an MOT? If so I need to change the sensor, how did you do it koooowweeee?

No I've not got anything to cancel the code. But I could take it to a garage.

You just unscrew it with a spanner and unplug it at the other end. Very easy to do. The part was £19 delivered off eBay

Disconnect the battery for half an hour

Jamie

I was going to do that but I need to find the radio code first or it will do my head in haha.

Will I unplugged it for half a hour or so. It's turned the light off. Not sure if that has fixed the fault until I get the emissions tested again

No I've not got anything to cancel the code. But I could take it to a garage.

You just unscrew it with a spanner and unplug it at the other end. Very easy to do. The part was £19 delivered off eBay

Easy to access given the exhaust shield?

Yeah very easy to access. Only a few mins to do.