Q: Would you be able to give me an estimate range for a code P0421 Low catalyst efficiency bank on a 2002 Mitsubishi Galant?

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I got an estimate for about $3000 to fix a code that came up on my check engine light. It is code P0421 for low catalyst efficiency bank. I was hoping you could give me an honest and true estimate of a range.

My car has 139770 miles.
My car has an automatic transmission.

As you know, code P0421 relates to the catalytic converter not properly working. In some cases, this may also be related to a faulty oxygen sensor or bad wiring to the oxygen sensor, however usually these codes will also be triggered. The ECU uses data from the upstream and downstream oxygen sensors to determine whether the catalytic converter is properly doing its job. I would suggest having an expert from Yourmechanic come to your location to take a look at the vehicle to properly diagnose the problem.

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