Nothing?

 

Check your spark plugs and wires. I had a bad distrubutor (Mercury Cougar) with this code. But we have a coil-on-plug system. I'm sure you can google how to check that. You could also have a leak in your exhuast. Have you upgraded your exhaust system (other than just a cat or axle back)?

Also, give us some info on your car please

EDIT:
Here's what I found from Google.
•Leaded fuel was used where unleaded was called for
•An oxygen sensor is not reading (functioning) properly
•The engine coolant temperature sensor is not working properly
•Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
•Retarded spark timing
•The oxygen sensors in front and behind the converter are reporting too similar of readings

And solutions:
•Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
•Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
•Inspect the downstream heated oxygen sensor (HO2), replace if necessary
•Replace the catalytic converter

 

Can be an o2 sensor issue but don't quote me on it.

 

I just noticed the second code is a pending code. Try clearing the codes to see if it comes back. I'm willing to guess one of your ignition coils is on it's way out and it skipped it's ignition cycle at the higher rpms.

 

TAKE it to the dealer 8Years 80,000 Miles....and Honda might goodwill it if ur over 80k

 

When that code P0420 comes up for me for any car in the past, it means the cat is shot and needs to be replaced. On RSX, i've resolved 3-4 cars from this issue after replacing a rusted out / has a hole in cat.

 

exactly what this guy said. Its extremely unlikely that a sensor is bad. 99% of the time the sensors are working properly and the cat is just bad. Depending on what state you live in it could be covered under emissions warranty. In ca on certain cars they have upto 10 years 150k mile warranty on certain emissions items!

 

I don't have warranty on my car. Not an option for me.
Should I start with replacing the O2 sensor?
Or should I go ahead and look for a cat? If so, which cat system is CARB Legal?

 

It doesn't matter if you have a warranty on your car or not, the Cat Converter is FEDERALLY MANDATED to an 8 year 80,000 mile warranty.

So unless you're over 80k, then it should be covered.

It's almost certainly your cat converter, that code means the secondary O2 that monitors emissions past the cat is reading too many emissions so either you don't have a cat, or the cat isn't doing it's job anymore.

 

its not the cat. it means the o2 is reading the air running thru the cat is not as clean as it should be. if you have fp disable the secondary o2 and your good to go. it happened to me a while back.

 

I don't have a Flash Pro. By the way, my car is a 2006 Honda Civic LX Sedan Automatic..

 

P0420: Intake Manifold THC content below threshold.

w00t692 is almost certainly right; I used to get this code with a race header (it replaces the catalytic converter.) Diagnostic codes/descriptions are all very specific, even if they're mostly written in techie jargon. Something is probably up with your catalytic converter. For this code to throw, it has to detect an imbalance for something like 30 consecutive miles -- it wouldn't be a result of an isolated incident, like flooring it to overtake on the highway.

 

as I mentioned before, its the cat, If i recall by memory, primary is P1166 and P0134 is the code for the secondary sensor. Get it replaced at the dealer or have a buddy who is willing to swap with you and have your friend who is still under warranty to get the cat replaced if warranty is an issue for you.

 

Don't know anyone that drives an 8th gen civic. My car is a Salvage Title in California, pretty sure dealers won't honor the warranty on the cat. It has only 65k miles on it. I'm guessing I'll have to pay the money to replace it? Does aftermarket ones work or do I have to go to dealer and let them take care of it?

 

I'd buy an oem cat, the aftermarket ones are usually cheapos and never last long. I'd check out the dealer, you never know might get it replaced for free, try it out

 

I'll probably have to wait for the engine light to come back on then? I deleted the engine light and drove for about 25 miles already, no engine light yet.

 

Don't just go buying random parts and start slapping them on!

It is most likely the cat, my car had the same code, new cat=no codes.

aftermarket is fine, go to an exhaust shop they will cut out and weld in a new one for a decent price! Got mine for 250 after taxes(in Canada) comes with a 3 year 60 000km warranty. An OEM cat will run you 1000+

edit: Your light will come back

 

Don't go after market trust me, it's not worth it. I just found an oem cat for like 320 bucks from college hills honda

 

and oem cat is pretty much your only legal option in Ca...

Does not necessarily need to be new either

 

Everyone who has said CAT is correct, if it was the O2 sensor, it would throw a code specific to the o2 sensor (like PO138).

 

Dealer said they won't replace it. :[

 

is that's because it's salvaged?

 

You can buy an aftermarket cat for your car for $220 shipped on ebay. It will be direct bolt on and it comes with a donut gasket too. Where in California are you? If you are in So Cal Los Angeles area and need help, let me know. Also, I don't know if I missed it somewhere but do you really need to get the code clear for whatever reason? ie, smog, inspection? If not, you can wait until you do to get it resolve.

 

Too late now.. I already paid the dealer $725 for installation + new catalytic converter

I feel like I made a bad decision.. =/ The cat was $500, installation was $200.. CA tax ~ $725 total. I'm in Northern California. Oh well.. I guess I don't have to worry about my emission anymore after this.. hopefully..

 

That's total bull****, man. I had a catalytic converter installed on my Chevy years back for no more than 260$, parts and labor. I understand it's a honda, but 500$ difference? You gotta be shittin me.

 

I know :[.. the catalytic converter was $500.. The installation is $200.. So expensive!! Stupid California legal things..!

 

could of bought an used one for $300 at most and it takes 20 minutes for installation or somone to install it for $50 dollars. A friend of mine who used to work for me is located in SF and he sure could of installed it for you for $50 dollars.

 

wow talk about a mark up. At least it's fixed, that should be good for 100k

 

^^^Hopefully it'll last.

Man.. this really sucks though =/ $725 out of the pocket. I checked for a new part, College Hill Honda was selling it for $310. My dealer from Honda estore price was $489..

 

You are so dumb lol. Sorry, I just had to say it. Next time, before you start pissing away your money look at your alternatives.