CAT Efficiency

luckyjoe

Well-known member
Oct 10, 2004
455
118
New Jersey USA
What can contribute to a P0420 fault code (Catalyst System Efficiency Below Threshold)? Beside faulty CAT(s)...

My D1 has thrown a P0420 code twice in the past two months. New Y-pipe/dual CATs were installed ~11 months ago, to replace the original Y-pipe when the bank-1 CAT blew it's guts out - causing a loud rattle and blowing exhaust sound. This failure also resulted in a P0420 code! Present replacement exhaust sound fine, but the code returns...

So, am I unlucky with CATs, or are there other issues I should check out first?

I may swap the bank-1 O2 sensors with the bank-2 sensors to see if the fault code also jumps from bank-1 to bank-2.

Regards,

Tom P.
 
Oct 27, 2004
3,000
4
I have not on any car brand seen a P0420 code caused by anything other then cat failure.

Were these aftermarket cats you installed?
 
Oct 27, 2004
3,000
4
Aftermarket may BE the reason you go tthe code. I have seen quite a few aftermarket cats still not clean the exhsut enough to make the computer happy.

I'm curious if your engine isn't casuing the cats to die. Any word on your fuel trim?

A rich mixture will wipe out cats too.
 

luckyjoe

Well-known member
Oct 10, 2004
455
118
New Jersey USA
I thought about richness, since it is a *feature* of these engines...

So, how do I go about evaluating the fuel trim?

Regards,

Tom P.