What if I bought the car second hand at a dealer? my 08 Forenza is showing problems with the downstream O2 sensor possibly the cat converter. I doubt the emissions warranty still appliesYou can try replacing the sensor, but I almost guarantee that code will come back. The converter is no longer working properly. They are covered under emissions warranty so you might as will get it fixed for free. Under warranty the front converter and the entire pipe from the rear of the motor to the muffler gets replaced (in order to replace the other converter as well). In Canada emissions warranty is 7 years 130kilometers, so you are well under that. And yes I've seen converters fail early, and some I've seen them last 250k as well. To replace both converters is well over $1000 so I suggest booking an apppointment ASAP and DONT clear the MIL.