1999 Mitsubishi Galant 99 Mitsu Galant-P0421 Failed NYS Ins

117,100 MILES • 4 CYL • 2WD • AUTOMATIC
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KENDU90
  • MEMBER
  • 20 POSTS
Hello,

I've had this P0421 code for the last couple of years and have passed at least 2 emissions inspections. The light has been on for about a month before I turned it off. I just started experiencing the dreaded sulfur smell from time to time. I failed my inspection yesterday because I thought I could fool the computer by clearing the codes. Now, I have to wait for a drive cycle to complete. Since I am now getting the sulfur smell do I definitely need a new Catalytic converter? Or will a new O2 sensor do the trick. I have been quoted $255 for replacing the downstream O2. What should I expect from having to replace the Cat?
Aug 27, 2008 at 4:00 PM
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RASMATAZ
  • ✓Experienced Mechanic
  • 75,988 POSTS
OBD2 P0421 may mean that one or more of the following has happened:

The catalytic converter is no longer functioning properly

An oxygen sensor is not reading (functioning) properly

A sparkplug is fouled up

New downstream O2 sensor might do the trick-The Cat can cost up to 2K USD.
Aug 27, 2008 at 7:56 PM
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