P0421 comes and goes

[faral]

my car has been throwing the P0421 code...and then turning it off on its own for the past 4 months. It'll stay on for 2 weeks. Go away for 2 weeks. Repeat. I haven't done squat to it.

I've read for this code, it's either 1) bad o2 sensor, 2) bad cat, 3) exhaust leak. But with any of those...why would the code clear it self repeatedly? it's weird!!!

 

[Hazardous PR5]

Code 0421 denotes the cat isn't heating up fast enough. I'm going through troubleshooting for this code right now and it seams I'll need to replace my cat. As for your codes deleting themselves? Are you sure the OBD2 reader isn't deleting the codes when you check them?