DIAGNOSTIC SHOWS P0420,HOW DO I REPAIR THAT.

1997 Mercury Marquis

Tiny

debbie taufi

June, 8, 2012 AT 4:36 PM

Catalyst system Efficiency Below Threshold Bank 1 is what shows up. Took it in auto zone did a diagnostic and showed cadalack coverter. But today showed the P0420

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P0420 Cat Converter

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1 Answer

Tiny

hmac300

June, 8, 2012 AT 4:48 PM

Best to have a pro look at it. It can be a converter bad, a coolant leak cooling off the converter, a bad O2 sensor, many things.

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