Check engine light 0420

[ASRACER4]

changed cat to aftermarket unit replaced o2 sensors installed
plugs and wires. any ideas to why the light comes on. after resetting
cel its fine for a couple hours,
thanks

[roadrash]

Search this site for the actual error code number, I think it should be "P0420." That should give you some info to start with. My guess is that either the cat is defective, or it just doesn't perform as well as the stock BMW cat.

Which aftermarket catalytic converter did you install??