Thread: Permanent P0420
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Old 05-08-2017, 01:45 AM   #7 (permalink)
Alexwallace23
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Quote:
Originally Posted by Wilson2608 View Post
Could you specify what exactly that code is. Sounds like your talking about a cat code. If you have high flow cats and no tune there is a good chance you will throw a cel. When I had my HFC nothing would keep the CEL off until I had the car tuned and the CEL deleted.
P0420 is Catalyst System Efficiency Below Threshold (bank 1). Just by looking at the code description you would think it's a cat converter problem but the possible problems are:

Faulty catalytic converter
Engine misfire
Fuel injector leaking
Engine mechanical damage
Oxygen sensor that has improper readings
Exhaust leak

I think it's an oxygen senor issue since the code comes and goes after a day. I do have HFCs with a tune. This code first came up after about 12,000 miles after the HFC install. I actually went a couple months after the HFC install before I got the tune and I didn't have any CELs.

I will test the O2 sensors soon and see how that goes.

Last edited by Alexwallace23; 05-08-2017 at 01:52 AM.
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