My inlaws have a 2001 Montero limited, which when given some gas I can hear a massive exhaust leak, in addition the check engine light is on. Upon a quick inspection I could see that the Catalytic converter is literally cracked in half. I ran diagnostic check and pulled the codes P0400 and P0431. I know the Cat needs to be replaced and maybe the egr sensor. I plan on digging into it this week to try and repair it myself.
Just wanted to see if anyone had any other suggestions/recommendations to check while I'm at it. Additional note, the engine was replaced around 40k miles ago and runs strong.

 

For EGR code (P0400) check to make sure the ERG valve operates properly AND that there is no debris clogging the pipe or valve ports. If those components work as intended, you may need new ERG solenoid. If you do, make sure to get MITSUBISHI solenoid. The aftermarket ones do not work too well. Before you replace any ERG related parts, check all vacuum lines and their routing. A cracked or incorrectly routed vacuum line will cause a malfunction.