Codes P0158-FF and P0420-FF

MB-POWER

MEMBER
2008 MERCURY MARQUIS
4.6L
V8
RWD
AUTOMATIC
235,123 MILES

Hi every body,
is there any way to clear this code (P0420) without replacing catalyst system? It is too expensive!
So, can I cancel catalyst system and replace only oxygen sensors then clear the codes?
Any help please.
Thanks

3 Replies

STEVE W.

MECHANIC
13,655 POSTS

Well, you have two different banks in question. P0158 is a code for a high second O2 sensor on bank 2 while the P0420 is for a bad cat on bank 1.

I would look at the voltages being reported by all four of the sensors upstream and down. If the rear sensor on bank one tracks along with the upstream one then the catalytic converter is junk. If however it is not then I would change both downstream sensors clear the codes and test again.

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Thursday, August 3rd, 2017 AT 12:10 PM

MB-POWER

MEMBER
80 POSTS

What about if I clean and discharge inside of the CAT, and replace both of O2 downstream sensors?
Thanks

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Friday, August 4th, 2017 AT 11:42 PM

KEN L

MASTER CERTIFIED MECHANIC
48,666 POSTS

Hello,

We have had very little luck cleaning a catalytic converters it best to replace it.

Here is a guide that will help you get the job done.

https://www.2carpros.com/articles/catalytic-converter-replacement

Please let us know what happens.

Cheers, Ken

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Monday, August 7th, 2017 AT 11:04 AM