Car Wont Start after Pedal Dance

[jhuman]

Hello folks,

I have an 03 Sentra with about 148K miles on it. A couple months ago I got the dreaded check engine light coming on, checked the code and got p0420. So I changed both the lower O2 (which is supposed to be what p0420 corresponds to) as well as the upper O2 sensor just to be safe. After I changed them, I performed the pedal dance (turn the car on, wait 3 secs, fully depress accelerator 5x in under 5 secs, wait 7 secs, depress accelerator again for 10 secs) to get the diagnostic mode then held the pedal down for another 10 secs, turn the car off, while continuing to depress the pedal for an additional 10 secs. I restart the car, the code goes away and stays gone for about 3 weeks. Two weekends ago, the check engine light comes back on, p0420 again, I pedal dance before a two hour trip, it goes away for 45 min and comes back on. Fast forward to this afternoon when I turn the car on and everything is fine. Pedal dance again, turn the car on and it fires up and then just dies instantly. I keep turning the key and sometimes it fires up and dies, other times it just keeps cranking and doesn't turn over. I waited a few hours. Still the same. Will try to start it again in the morning but I'm completely lost. Did I terribly flood something? Should I just call a mechanic? please help

[dorcom]

1st : Stop the "pedal dance"! Take your wife or GF instead to dance....!
2nd : Don't go crazy about the check engine light! As long as the car drives...
3rd : P0420 code: Catalyst System Efficiency Below Threshold (SNAFU)

The catalyst system being referred to is your three-way catalytic converter; so the catalytic converter is not working properly (i.e. it's not efficient). Bank 1 refers to the side of the engine which contains cylinder #1. On inline engines such as 4 & 5 cylinder engines, there is only one bank. So, really simply said, the efficiency of the catalytic converter and/or exhaust pipe and/or O2 sensor is not so great.

Possible solutions:
New CAT?
Obstruction in exhaust pipe or CAT?
O2 sensor.

What else did you do aka "dance" ?

[SoundEfx]

Changing the cat is one way of fixing the issue.
Another way of getting rid of the code while you're saving up for possibly a new cat, is to implement the 'anti-fouler' method.
Google it and you should see some examples of what I'm talking about.