Honda Civic 8th Generation: P0420

[Distorted Vision]

Engine Management Light coming on intermittently with P0420.

Had same fault code 12 months ago and had the pre-catalytic lambda sensor replaced. Engine was running rich. Carbon deposits around exhaust fuel economy halved.

Currently, no symptoms and fuel economy normal at 40mpg. Think this time that the catalytic converter needs replacing. Tried 10 treatments of Cataclean and 2 treatments of BG 44k Platinum. Had exhaust checked by Kwik Fit and checked the spark plugs myself.

Apart from the catalytic converter the post cat lambda sensor could causing the fault code. But there is a different fault code.

[Belle427]

You would normally look at live data on the post cat sensor, if its mirroring what the pre cat one is doing its normally a cat problem. It should remain at a stable lower output without getting too technical.
Sounds like the cat is faulty if the car appears to be running well in all other aspects and no exhaust leaks.

[Distorted Vision]

I ordered a BM Catalyst from Arnold Clark and a local garage have quoted £105 to install.
I also ordered a Bosch post catalytic lambda sensor.

Hope they aren't going to charge extra to install it.
Hope this will resolve this P0420 issue.

I've tried 10 treatments of Cataclean and 2 treatments of BG 44K Platinum.
Didn't try the Scott Kilmer Lacquer Thinner solution. Seemed potentially hazardous to me.

Currently 10% discount on eBay: CRISP10 which I used to purchase the two parts.

Edited by Distorted Vision on Monday 4th November 23:18

Edited by Distorted Vision on Monday 4th November 23:24