Stock 2000 EM1 with 120,000 mi. "consumes" 3/4 quart 5w30 every 4000 mi. Got the P0420 Cel and understand the ECU thinks the catalytic converter is operating inefficiently. Primary O2 oscillations aren't being smoothed out as read by secondary O2 sensor. Is this typically a clear cut case of replacing the cat? Or can this CEL be caused by a leak between the A pipe and cat? Debating what parts I should throw at this problem before buying a $400+ cat.

If I do have to replace the CAT, what else should I check out...because I dont think it should be going bad after only 120,000 mi. My ignition system is in top notch condition. PCV valve is always good.

 

your motor is eating 3/4 your motor oil every 4k miles...

if it is that's a lot of oil your motor is burning...thus probably why your cat is going...

 

3/4 quart, not 3/4 of the total engine oil...no blue smoke out the rear, and my back bumper ISNT black... you really think that's a lot?

I know plenty of others burning more who dont have cat problems..yet.