OBD II Code P0420 1997 1.8 Mirage LS 145,00 miles
 

Been having intermittant Check Engine light problems. Found out today that it is a Catalyst System Efficiency below Threshold. From what tech said it needs a new catalytic converter. Is this something you can do yourself. Also any ideas on cost. He said universal with welding would $80 plus os oem would be upwards of $400. Any thoughts and recommendations. Runs good except on real fast acceleration...guessing that is caused by cat converter being clogged. Thanks for any and all help.

This is a very common code. I am myself experiencing the same check engine light. There are a number of alternative fixes you can try before spending the big bucks.

P0420 Mitsubishi Catalyst System Efficiency Below Threshold Bank 1 OBDII Engine Light Trouble Code | Engine-Codes.com

Changing O2 sensors is another possible cheaper alternative, and has resolved the issue from some people. I would hate to spend that much money and all it needed was a new O2 sensor.

For me the light is not permanently on and everything I've read says this is a code you ignore until you do see performance loss.

Thanks BCloud for the info. What I've done is to clear code by disconnecting battery cable. I have driven it about a week(300 miles) and have not noticed anything. Today I will check my gas mileage to see what it is now.

can you positionally weld thinwall pipe?
Yes? You can diy.
No? You cant.

Issues under heavy load can stem from any number of things.
Try the cheap options first.