Mot fail co reading .700

321p123

Hu guys just back from failed mot on my zafira 1.8 petrol, as above massive fail on the co emissions.
Mechanic jumped straight to the cat, as I'd cleared the emissions fault code before mot, this usually works....
Car driving fine for its age 16, and no smell etc, not many miles done per year, could it be a lambda sensor? 
Please any help appreciated, the mechanics didn't seem the friendliest of people and didn't want to know etc.

321p123

Used redex 2 weeks ago also, don't know if this could affect the co readings 

born_again

Perhaps find out exactly what the fault code related to?

Arunmor

Try a bit of Italian tuning.

321p123

Thanks, so The p0420 fault code, my car failed the last 2 mot with same issue but got through usually after additives or re test

Baldytyke88

Is the engine well looked after?

What state are the spark plugs in?

321p123

Oil and filter and air filter done 2k miles ago, the spark plugs seem OK as in car seems to drive fine etc, they also failed a caliper which was changed at the same time as oil change etc so I'm a bit like hmmmm, saying that they reckon they are too busy to look at it for 2 weeks at least .....

Mildly_Miffed

One of the jobs of the cat is to oxidise CO (Carbon Monoxide) into CO2 (Carbon Dioxide).

So if your CO is high - and it is, pass limit is 0.2%, so 0.7% is 3.5x that - then cat is definitely the first suspect.

What fault code are you clearing? Post-cat lambda? That's telling you that the cat's not working, too. Pre-cat lambda is used to adjust fuelling, post-cat lambda is used to monitor the cat.

If you were getting the post-cat lambda fault, but the emissions were correct, then the post-cat lambda would be suspect.

321p123

Is it normal to be double the co2 emissions if the car is just not run enough ? Or would this be lower level fail 

321p123

Mildly_Miffed said:

One of the jobs of the cat is to oxidise CO (Carbon Monoxide) into CO2 (Carbon Dioxide).

So if your CO is high - and it is, pass limit is 0.2%, so 0.7% is 3.5x that - then cat is definitely the first suspect.

What fault code are you clearing? Post-cat lambda? That's telling you that the cat's not working, too. Pre-cat lambda is used to adjust fuelling, post-cat lambda is used to monitor the cat.

If you were getting the post-cat lambda fault, but the emissions were correct, then the post-cat lambda would be suspect.

The fault code is po420, how much do one of these buggers cost to replace in labour lol. I think I should probably do it myself if I can and hope the corrosion not too bad 

400ixl

Baldytyke88 said:

Is the engine well looked after?

Given the history of previous failed tests and the fixes being clearing codes and throwing some Redex at it, the answer to that is no.

The code is for an under efficient catalytic converter. You need to fix the cause of the problem, not try to bodge it. It could be a lamda sensor, but given how long it may have been faulty I wouldn't be surprised if it hasn't now killed the catalytic convertor and that will need replacing as well.

A competent garage can test the lamda sensor, but the cat will need to be inspected as well.