P0421 Mitsi code in a 2006 Gallant GTS - indicates that O2 sensors have picked up a problem with the operation/performance of the #1 bank catalytic converter (about $800) What is the chance that cleaning the sensors or adding a gasoline additive that says it will gaurentee a passing emision test will make the code reset long enough to pass emisions test - anyone?
there is a small chance it might work.
You can try to use non-fouler, it works for some people
http://www.club3g.com/forum/performance/55284-how-fix-ses-error-code-p0421-about-5-bucks.html
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