Rep Power: 150

Seemed to me my 01 LX 5sp (177k miles) has been running normally. I hadn't driven it for a couple of days.
Monday: we had a lot of rain when I drove again to work. After about 10 miles of driving the CEL appeared... but the car seemed to be running fine to me, no hiccups.

Tuesday: I stopped by the Danger Zone and used the code reader. Cleared the code and when I got home I took a look at the down stream o2 sensor. All seemed normal. On the way home I ran the engine up to 4500 rpm in 2nd and it pulled strong and smooth.

Wed: Driving home and sitting in a long line of traffic at idle the engine started to struggle and seemed very slow to respond to throttle input. The CEL came back on 30 seconds later. I was worried it was going to cut off on me, but the idle smoothed out!
The engine sounded better and the car seemed to have more pep than its had lately!

Thurs: The CEL is still on but it's still running great. More fun to drive.

I hope the CAT isn't bad and this was a moisture issue with a o2 sensor connector. If the CEL doesn't clear itself I'll go back to the DZ and see what the code is and clear it again.
I've no interest in replacing parts or spending money when it is running smooth and has power. I don't normally rev it past 3k and I'm still getting 33-34 mpg on the winter blend.

If the only code is p0420, it indicates what? I'm not getting a code for an o2 sensor or anything else. No strange smells...

 
Rep Power: 519

The basic meaning is the cat has lost efficiency. It's substrate has lost a significant portion of its ability to store and release Oxygen.

It does not automatically mean it has clogged or become a restriction.
Assuming it's not a false positive.

Does this happen with any frequency? If it did not set a code for sensors or fuel trims---only reset the cat code, I'd be interested in using a good scanner to graph out the o2 sensors and fuel trims while this event occurs.

 
Rep Power: 150

The only time its ever stumbled or had non responsive throttle was yesterday. By the time the CEL came on it was running normal again. Actually better than normal, seemed like it had more power. Enjoyed the drive home today more than usual because its seems to have more power.

I've had the car almost 2 years. No temp issues, only CELs have been CPS sensor (Feb 2015) & primary o2 sensor (Oct 2014).

 
Rep Power: 230

Ya bro that means your cat needs some weed/catnip.

troll'lolol

 
Rep Power: 519

My cat stole all my lighters and zigzags. I think I need to sign her up for one of those 12 step programs.

 
Rep Power: 150

On my way home from work the CEL cleared!
Its still running great, no engine hiccups.

I'll wait and see when it comes back, but I'm in no hurry to spend money, especially when its running good.

 
Rep Power: 0

When the cat become less efficient it does not affect the driving in any way.
Pull away the O2 sensor using Modified non fouler or build a circuit
Google p0420 fix

 
Rep Power: 211

Sounds like Toonces likes to get after it... driving cars and huffing ganj:

 
Rep Power: 150

Thanks a lot for showing me this, I wasn't aware of these options. That's my next move when the code comes back!

 
Rep Power: 0

You are welcome

 
Rep Power: 150

UPDATE:
The P0420 has tripped the CEL 1 more times since my original post.
So I bought the resistor and capacitor to add a low pass filter to my secondary o2 sensor.
I will take some pictures when I get it wired up.
The components cost me $2.83.

 
Rep Power: 150

Installed a new Denso sensor with a low pass filter today. I forgot to take pictues before I heat shrinked over the soldered components. I was doing it on lunch break at work & was in a rush.
Hopefully no more CEL!

 
Rep Power: 150

UPDATE: My CEL has been off. No return of the p0420 code. But I can't say what has solved it. Likely its the new Denso o2 sensor.
Please note the low pass filter will not work if you do not have a catalytic converter that is functioning.