Mercury Marquis P Codes (Powertrain) P0400 - P0499 P0420

Browse Mercury Marquis P Codes (Powertrain) P0400 - P0499 P0420 questions and answers. Choose a question that matches your symptoms.

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PO420 On 2000 Grand Marquis

2000 MERCURY MARQUIS
I Recently Had The Po 420 Code Show Up On My Grand Marquis. I've Replaced The Downstream O2 Sensor On Bank One. It Didn't Fix The Problem...
1 ANSWER
Asked by gnorton52

Diagnostic Shows P0420,how Do I Repair That.

1997 MERCURY MARQUIS
Catalyst System Efficiency Below Threshold Bank 1 Is What Shows Up. Took It In Auto Zone Did A Diagnostic And Showed Cadalack Coverter. But...
1 ANSWER
Asked by debbie taufi

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