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Tim Mohr
Tim Mohr, ase master
Category: Mitsubishi
Satisfied Customers: 15708
Experience:  30 yrs foriegn and domestic, gas and diesel
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2003 Mitsubishi: Lancer..a trouble code P0421, What is the fix

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2003 Mitsubishi (Lancer) has a trouble code P0421, What is the fix for this problem and how do you reset the engine light ? Thanks, Joe
Hi, my name is XXXXX XXXXX code os for the cat converter inefficiency, it is caused by either a bad cat converter, or a bad downstream o2 sensor, after the cat, the first thing to do is replace the downstream o2 sensor, if the code returns, then you will need a new cat converter,Tim
Customer: replied 5 years ago.
You didn't tell me how to reset the lite
Customer: replied 5 years ago.
You didn't tell me how to reset the lite, and is there a way to test the O2 sensors?
the light wont reset, until the problem is fixed, then you will need a scanner or a code reader to clear the codes, disconnecting the battery wont clear the codes on this, they must be cleared with a scanner or code reader, most parts houses, like Autozone will do this for free, to check the o2 sensor, you will need a scanner with data capabilties, to monitor the signal and seeing if it switches, or stays low, how many miles do you have on this?
Customer: replied 5 years ago.
120 plus
then it most likely is a bad cat converter, we usually replace these at about 130k,Tim
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