How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Tim Mohr Your Own Question
Tim Mohr
Tim Mohr, ase master
Category: Mitsubishi
Satisfied Customers: 14997
Experience:  30 yrs foriegn and domestic, gas and diesel
Type Your Mitsubishi Question Here...
Tim Mohr is online now
A new question is answered every 9 seconds

2003 Mitsubishi: Lancer..a trouble code P0421, What is the fix

This answer was rated:

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 4 years ago.
You didn't tell me how to reset the lite
Customer: replied 4 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 4 years ago.
120 plus
then it most likely is a bad cat converter, we usually replace these at about 130k,Tim
Tim Mohr and 4 other Mitsubishi Specialists are ready to help you

Related Mitsubishi Questions