Rep Power: 0

Hi there, I have a 2005 EX 1.7L coupe with 215K miles. I'll do some of the work on my car and recently I changed out the stock intake to a cold air intake. Since the switch a P0420 will come on for a period of time and then drop and come back on again a couple of days later. I don't know if it has something to do with the intake switch or maybe with the oil. There are two scenarios that, with time the code will drop: one, if I drive under 50mph for a couple of days and the other is adding oil when it's low. Keep in mind that the engine temp has never, yet, raised above standard. The engine light is not blinking.

Could a sensor be going bad and the intake exaggerated the symptoms? Maybe the same could be said for the engine leaking/burning oil. It does have a boatload of miles on it and there have been a couple of occasions where I ran the oil low. Also I use Pennzoil full synthetic oil in the car if that makes a difference.

Is there a way to test these theories? Any help is appreciated, thanks.

 
Rep Power: 242

That code is a catalyst efficiency code. Catalytic converter worn out or the sensor. You can pull the secondary O2 sensor out and clean it. Or leave it out of the exhaust stream and see if the code stays gone.

 
Rep Power: 221

Cat is probably on the way out. With the code being intermittent you can try using one of those cat cleaner products that you pour in the gas tank. I had it work on one of my 05s

 
Rep Power: 0

Thank you, I'll give that a shot!

 
Rep Power: 0

Hi quick question for anybody who may know, I have been getting this code off and on since I have installed my catless headers on my 01 LX. Would this be from the headers having no cats or could it be one of the O2 sensors

 
Rep Power: 221

Take a wild guess...

You gain nothing from removing the cat(s), put them back.