Ill first apologize if this has been covered before, i was just to lazy to search.

I have a 2004 Galant ES with 78000 miles.

Driving saturday night my 'SVS' light came on. Sunday morning i had it scanned and the probable cause is:

1. Exhaust leak near rear o2
2. faulty rear o2
3. Faulty catalytic converter

But today the light didnt come on. do we think its the cat, or o2?

 

I would test the 02 sensor first with a DVM or DOM.