DIAGNOSTIC SHOWS P0420,HOW DO I REPAIR THAT.

  • Tiny
  • debbie taufi
  • 1997 Mercury Marquis
  • 90,000 miles

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

Friday, June 8th, 2012 AT 4:36 PM

1 Answer

  • Tiny
  • hmac300
  • Expert
  • 42,126 posts

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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Friday, June 8th, 2012 AT 4:48 PM

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