codes P0158-FF and P0420-FF

2008 MERCURY MARQUIS
235,123 MILES • 4.6L • V8 • RWD • AUTOMATIC
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MB-POWER
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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
Aug 3, 2017 at 9:14 AM
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STEVE W.
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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.

Aug 3, 2017 at 12:10 PM
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MB-POWER
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What about if I clean and discharge inside of the CAT, and replace both of O2 downstream sensors?
thanks
Aug 4, 2017 at 11:42 PM
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STRAILER
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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



Aug 7, 2017 at 11:04 AM