P0420 Catalyst System Efficiency Below Threshold

[Gorbstein]

Just got an engine light, plugged her in and got this:

P0420 -- Catalyst System Efficiency Below Threshold (Bank 1)

This is a 2006 1.4 16V Sport 75PS (BKY engine)

Now, 3 weeks ago I dropped £350 on a whole new exhaust system including both new cats, so unless I received faulty parts I doubt the cat is at fault. I suspected a rear lambda, but from digging a little deeper I'm not sure my car even has one?

I can say there's a bit of a uncharacteristic petrolly smell when I start her up at first, but this could be a symptom of the suddenly cold weather up here.

Any other ideas?

 

[Chino_UK]

My first instinct would be lambda, maybe leaky exhaust gasket ?

 

[Gorbstein]

My first instinct would be lambda, maybe leaky exhaust gasket ?

Yup, the gasket crossed my mind, how best to check?

 

[Gorbstein]

Well, fingers crossed it was a glitch. Had a look at the manifold and exhaust/cat with the engine running and it looks ok. Cleared the fault and have covered about 80 miles today without incident. If it shows up again I'll start looking at the lambda. If it isn't that, it won't hurt to have a spare sensor as I assume it will go eventually.

 

[Gorbstein]

Hate leaving threads unfinished, so just for the record, I resolved this by replacing the front lambda sensor. Light has not returned in 350 miles so I claim a victory

Car also drives better too, and is using significantly less fuel. The only side effect is that the idle is much lower than ever, perhaps mine has always been off.