there was actually a recall on converter issues for your vehicle in which warranty was extended, and then a pcm(powertrain control module) updating as required after converter replacement, depending upon which computer is in your vehicle. You need to take it in so that dealer can see if your car's computer is one of the ones listed in recall so that the updating can be done, which will take care of the light being back on.
Here is recall you can print and take with you:
Attachments are only available to registered users.
DATE: December, 2005
This TSB supercedes EMR-05-001REV, issued October 2005, to update the PCM reprogramming database, which eliminates TPS reinitialization, and to update the warranty labor time.
Some affected vehicles have incorrect parameters in the Powertrain Control Module (PCM) software that may cause the warm-up catalytic converter to overheat and melt when the vehicle is repeatedly driven at wide-open throttle. For certain 2002-2003 vehicles, new warranty limits will apply to the warm-up catalytic converter, which are described in the CUSTOMER NOTIFICATION and WARRANTY INFORMATION sections of this bulletin.
A letter will be sent to all owners of affected vehicles, telling them to bring their vehicle to a Mitsubishi Motors dealer to have the PCM reprogrammed at no charge, and that if their vehicle has a SES lamp on for failure of the warm-up catalytic converter (DTC P0421), they will also receive a new warm-up catalytic converter.
In addition, owners will be advised that the new warranty coverage for the warm-up catalytic converter will be extended from 8 years/80,000 miles to a limit of 8 years/100,000 miles. Until February 28, 2006, replacement of the warm-up catalytic converter will be free of charge, regardless of vehicle mileage.
After February 28, 2006, all owners (regardless of vehicle mileage) will be entitled to the PCM reflash free of charge. However, warm-up catalytic converter replacement will not be covered under the warranty if a 2002-2003 model has over 100,000 miles (over 80,000 miles for 2004-2005 models). A copy of the customer notification letter is shown in this bulletin.
Before starting this campaign procedure, CHECK ON THE WARRANTY SUPERSCREEN to verify that the vehicle is an affected VIN for this campaign and that this campaign procedure has not already been completed.
Use the Genuine Mitsubishi Parts shown.
Refer to the flowchart shown.
Sample claim screens are shown.
Replacement Parts Storage and Retention:
Retain all replaced catalytic converters for at least five (5) days after the payment of the related campaign claim. The five days begins the day after the claim appears in the "Paid" section of your warranty claim statement. If the part is requested during those five days, you must return the part as indicated on the parts return request letter
The images that didnt show up, dont worry about, it is just information that dealer uses that they alreasdy have on file as they are just screen shots of the reprogramming procedure
It is free of charge per the recall. I have copied that part again and highlighted where it states mileage doesnt affect the free update:
After February 28, 2006, all owners (regardless of vehicle mileage) will be entitled to the PCM reflash free of charge. However, warm-up catalytic converter replacement will not be covered under the warranty if a 2002-2003 model has over 100,000 miles (over 80,000 miles for 2004-2005 models). A copy of the customer notification letter is shown in this bulletin
if you can provide the 17 digit VIN code, one of our experts has said he will look it up and see if yours is under this recall as far as the computer part number on yours
the other expert will pick up from here if you have the VIN code to provide and help with it further as I have to get offline to handle a family emergency. He will be right with you
Okay, we have a winner now.
The problem unfortunately is that you have replaced the wrong converter. The pre-cat (or "Warm-Up Catalytic Converter" as it was referred to above) that is built into the exhaust manifold is the only one that is monitored by the system; this is the converter that has failed. The post cat under the car that you replaced does not even have any provisions for the computer to know it is there, as the pre-cats on the manifold are sufficient to bring the vehicle within emissions standards.
The part information from recall that was posted earlier had this information however it was in one of the pictures that was not loading. Here is a copy of that section of the recall:
Just a moment, let me check the current price.... advanced warning you are probably going to want to be sitting down for it.
Give me just a minute to look it up.
Current retail price on your cat manifold is $390.52 (not as bad as some if that helps any).
Dealer cost is $240, so there is a lot of room to work if you have a friendly dealer that negotiates. If not, I would recommend calling mentormitsubishi.com (you will need to order over the phone, not from their site most likely due to the part you need). They will be probably about $100 less.... they usually sell for cost + 20% or so, they are a very inexpensive place to get factory parts.