What would be some sure tell symptoms of my cat going bad? I have had it on for like 6 months and the past 2 months I have been getting really bad gas mileage. Also I'm throwing a few codes on the ECU.

12 Exhaust Gas Recirculation System
54 Crankshaft Speed Fluctuation Sensor
61 Primary O-2 Sensor Circuit

Well those are the numbers my car flashes at me. Not sure if they are correct tho.
I'm going to be removing the cat this weekend and installing the stock one so I will know for sure if its the aftermarket cat. Just curious why I would get such bad gasmileage and less performance.


[Modified by Fooser, 8:48 PM 5/29/2002]

 

If it was a bad cat, you will get check code for the second 02 sensor, not the primary sensor. Something else might be wrong.

 

I will look into those sensors then and let you guys know if replacing them works.