P0421 mk3

[ARHarh]

Can someone help confirm my diagnosis?

I have a 2007 2.0 sport. It has started flashing up a p0421 code. So using the toque app I have investigated the lambda sensors. It appears that sensor 1 (pre cat) is not working as there is no voltage showing on the graph. Sensor 2 is responding ok. So if sensor 1 is not showing fluctuation in voltage is it broken? If it is can i replace it with a generic sensor?

Thanks for any help

[ARHarh]

No car is standard. I know where the sensors are.

[ARHarh]

Thanks

[ARHarh]

nickthecynic said:

SmilerFTM said:

The O2 sensors are both in the midpipe, have you had a new manifold without a cat built in fitted?

Smiler - if you're still on here, I'm getting P0421, have changed the sensors and fitted a new manifold without the pre-cat but still getting the EML every 50-70 miles. Is there something I need to know?

This was while ago. But It ended up being the manifold pre cat crumbling. A big lump of pre cat was blocking the airflow to the o2 sensor in the bottom of the manifold, this then blocked the main cat. New (second hand) manifold and new cat solved the problem. Been fine ever since and still in my ownership.