P0420 won't go away!

[EddThatch]

Make - Vauxhall
Model - Crossland X
Engine size/Type - 1.2
Year - 2018
Mileage - 66k

Help!
Have had a P0420 code come up for ages now. We have replaced the Catalytic converter, that didn't work. Replaced the Post Cat oxygen sensor (twice), that didn 't work. Sparks plugs have now all been changed as well. We have also had the exhaust checked for leaks but nothing there either.
We seem to be just throwing money at the problem and don't seem to be getting any answers.

Any advice would be greatly appreciated

 

[carmanmemoranda]

Impossible to say without more info

But it's usually the pre cat sensor that affects the most

 

[RandomGrinch]

We seem to be just throwing money at the problem and don't seem to be getting any answers.

Separately, it's also getting to the age where the wet timing belt deteriorates - if it hasn't yet had a belt change, this might be another upcoming expense.

 

[Burnerman]

In my experience, for what it's worth......
Use a quality catalytic converter - not the cheapest;
Use an OE sensor (the pre cat one - the post cat sensor is just checking the performance of the pre cat one );
Get the system bloody hot, then cancel the codes and see what happens.
Try a can full of Forte injector cleaner.
John

 

[EddThatch]

Separately, it's also getting to the age where the wet timing belt deteriorates - if it hasn't yet had a belt change, this might be another upcoming expense.

Just had that changed with the spark plugs. It was in a bad way. Code cleared after but came back 2 days later

 

[carmanmemoranda]

What symptoms have you got ?

Code info on its own means nothing

 

[Belle427]

As said only use genuine sensors or your ****ing in the wind, some introduce more problems.
Aftermarket cats are generally rubbish too.