Help! P0420 CODE

[danforth45]

My Fiance has a 99 civic w/ 93k.

About three months ago it started running wierd and to make a long story short it needed a tune up, new plugs and wires and she ran like new.

Less than a day later the CEL came on but it still ran good. FYE the car has NEVER had the CEL come on.

I had the code pulled and it is the P0420-" catalyst efficiency below threshold bank 1" code.

Her dad took it to his mechanic, (not the one I took it to) and they said it need a new Cat.

This didn't sound right to me since the car has low miles (93K) and the CEL just came on after my mechanic started probing around. Her dad is ready and willing to buy a new cat but I think it's something else like a sensor.

Any Ideas woud be greatly appreciated
Matt,

[tomsindahizouse]

I also had this same problem with my car when I first bought it. The kid that had it before me gutted out the catalytic converter and the 02 sensors were totally gone. I would visually inspect the 02 sensors first and if they look fine it could be a wiring issue. The wiring for the 02 sensor is pretty simple. If its not the 02 sensor it probably is the Catalytic converter...which you want to shop around for because they are like $700-$800 OEM. You should have taken the car back to the shop that worked on it when the CEL went on if it went on the day after they worked on it, but that seems like its in the past.

Good luck.

[GreenGeckoUSA]

I have the exact same thing wrong with my 98 civic (although i have 185k miles on it). I got a second and third opinion and was told that I could try replacing the o2 sensor(s) first and if that doesn't work, i'll have to get the cat replaced. The guy at Meineke said that since my car doesn't have any symptoms, I could probably drive it until I have to get the emissions tested (it won't pass with the code). The light went off after 120 miles and my gas mileage has stayed the same (contrary to what I was told would happen if the cat was bad). I am taking it back to Autozone to see if it's still giving the code even though the CEL is off. FYI: The three quotes I got to replace the cat and one o2 sensor were: 1) Honda: $1300-$1400 2)Meineke: $600-$700 and 3)local mechanic: $840. Good luck and keep me posted!

[siege911]

there was just a thread on this down below... but anyways, bank one means the first o2 sensor is gone, and it's giving making your catalyst system operate poorly (someone correct me if I'm wrong). same code came on my 98 ex, after 93k miles, and we replaced the 02 sensor and it was good. That's what I'd recommend doing. You'll need a special o2 sensor wrench to get it out, and it's kinda tough to get out, but it's better than payint 800 bucks for a new cat.

[danforth45]

thx ,for the help
FYI
the car doesn't have any mods whatsoever! no exaust, no headers, nothing! not even an intake.

She drives it easy and burns good fuel so i'm pretty stumped here.

I'm of your idea siege that it may be a o2 sensor.
but why would it go out right after a tune up?

[siege911]

they go out after so often... nothing on a car lasts forever... 93k miles is a long time for 1 o2 sensor

[danforth45]

i'm sorry, i meant the cat,
don't they last alot longer than that?
like 150k+ ?

[siege911]

they're supposed to, but things happen... bad o2 sensors can damage it, and gscivic just said that his went out on his brand new car after 15k miles... so things happen