Mine has 120,000 miles. Fortunately I live in a rural county without emission tests. The problem is when I have another problem I won't know it because the light is already on.
Papaw
Papaw
This is a note from the blowhard Texan as Cyclonerules91 calls me. I have a 02 Lancer as you do. Mine has the same problem. code PO421 is for a warmup cat. converter. They had a recall that was for 8 yrs or 100,000 miles. You can disconnect the battery cable and the light will go out temporarily. If you get it replaced be sure and have the computer reflashed or reprogrammed or it will melt your new cat.
Remember, this is coming from an Okie that lives in Texas and is now a blow hard Texan.
Papaw
Being an old man that has been through these kinds of problems, I have a good electrician, roofer, plumber, and AC guy to turn to.
Papaw