2005 EP3 threw a CEL (P0420, catalyst system efficiency below threshold bank 1)

[DRP967]

Hello, i have a 2005 EP3 with 149,042 miles. My car recently threw a check engine light (P0420, catalyst system efficiency below threshold bank 1) and my mechanic says my catalytic converter is going out. Im told there are no aftermarket cat applications for the 02-05 Civic Si and i need to use a OEM cat which will cost about $1,057 part # 18160-PNF-AO1. He told me not to worry about it until smog time. Here are my questions:

1. Are there aftermarket cats for the EP3 and are they legal/will pass smog in California?

2. My check engine light has been deleted but it came back obviously due to the cat converter efficiency, now since ill be rolling around with this light on, how will i know if something else is wrong with the car since its already showing a CEL?

3. Anyone else had to replace a cat yet? And how long does a cat usually last?

4. My friend who owns a shop tells me that he doesnt think its the cat, he thinks its possibly the 02 sensor(s). He says if the cat is bad then i should hear a tinny/metal sound down there, anyone can confirm truth to this?

*Thank you for any help, much appreciation.

[rice4u]

hey man i have had this problem for the past 6 months haha. here are the steps i have taken.
research, found out possible it could be the sensors, all mechanics will tell you its the cat 100%.
Bought a used oem cat from a member on here (yes takes chance on used cat. he claims it was good but who knows)
replaced my cat, p0420 went away, a new code came up, p1167, and i cannot even reset the code, it comes back as soon as i start the car
replaced the primary o2 sensor.
p0420 came up a few days later lol i can reset the code and it comes back after a few days
i been driving around with this code since then.

what im planning...
put my old cat back on and see what it gives me... if code stays
replace seccondary o2 sensor.
if fail, then replace with o2 defouler final solution

now i have a question for everyone:
what the hell is the difference between these 2 parts:
denso 234-4122
denso 234-4124

they are both for the same thing except... 4124 is way more expensive lol. u can google it...

[DRP967]

rice4u, thanks a bunch for the speedy and informative reply. Seems like it could be the sensors...might be trial and error here. Although 3K miles ago we changed out the 1st 02 sensor. Bump for more replies and rice4u's inquiry regarding the denso parts.

[rice4u]

no problem man, im trying to figure mine out as well. my smog is comming soon, so i need to get rid of the CEL. oh by the way my MPG is still around 28/30 so whatever it is, its not affecting my gas. i dont kontice anything at all as far as drivability or strange noise either.

all i can assume from what ive done is, my cat was good, my sensors were bad, i changed my good cat with a bad cat, and now i get other codes, i fix the original problem and now the initial code is back... at least that's what im hoping for haha. one way or another we will find out when i replace the seccondary sensor, and replace my original again...

[DRP967]

no problem man, im trying to figure mine out as well. my smog is comming soon, so i need to get rid of the CEL. oh by the way my MPG is still around 28/30 so whatever it is, its not affecting my gas. i dont kontice anything at all as far as drivability or strange noise either.

all i can assume from what ive done is, my cat was good, my sensors were bad, i changed my good cat with a bad cat, and now i get other codes, i fix the original problem and now the initial code is back... at least that's what im hoping for haha. one way or another we will find out when i replace the seccondary sensor, and replace my original again...

Same here, my car seems to be running fine and MPGs hasnt suffered. Good luck man, godspeed for a fix. I think its either the secondary sensor or the cat in my case, heck ill worry about it when smog time comes around. :mredface:

[rice4u]

i'll keep you updated with whatever i did to fix mine. im going to change my old cat back first since its free lol. then following that i will buy a new seccondary. very worst case, the defouler. my smog is in june :(

[DRP967]

i'll keep you updated with whatever i did to fix mine. im going to change my old cat back first since its free lol. then following that i will buy a new seccondary. very worst case, the defouler. my smog is in june :(

Awesome man, let me know what happens and good luck!

[civicSIracer]

same issue with me. buy a cat. there are NO carb aftermarket cats for the ep

[DRP967]

same issue with me. buy a cat. there are NO carb aftermarket cats for the ep

Thanks for the input, ill purchase a cat later down the road.

[dirtyduck17]

With the right OBD2 scan tool you can read the sensor outputs and determine if the sensor is bad or the cat. Or both. It's the second o2 sensor the determines if the cat is operating correctly. You could try a cat from another K-series car (accord, crv, element), used perferably to save money. Also. just FYI, the junk guys that visit dealerships and buy junk parts (starters, block, heads, trannys pay really well for used cats), you could recoup some of the cost of a replacement cat.

[DRP967]

With the right OBD2 scan tool you can read the sensor outputs and determine if the sensor is bad or the cat. Or both. It's the second o2 sensor the determines if the cat is operating correctly. You could try a cat from another K-series car (accord, crv, element), used perferably to save money. Also. just FYI, the junk guys that visit dealerships and buy junk parts (starters, block, heads, trannys pay really well for used cats), you could recoup some of the cost of a replacement cat.

Great info, thanks ill look into that.

[DRP967]

*Update*

My check engine light went off by itself 2 days ago has yet to come back on...is my car good now? lol

[superchargedk20]

look into magnaflow if u need a cat. They have tons of high flow cat options that are universal. I used it on my ep3 and I neve threw a code and it was only 50 bucks

[dirtyduck17]

*Update*

My check engine light went off by itself 2 days ago has yet to come back on...is my car good now? lol

My EP started throwing a 2nd O2 sensor malfunction code a while back. The CEL would come on and stay on then randomly turn off. I ran some stuff called terraclean through my fuel system and engine and haven't had a code since. I hope your CEL stays off. Good Luck!

[DRP967]

My EP started throwing a 2nd O2 sensor malfunction code a while back. The CEL would come on and stay on then randomly turn off. I ran some stuff called terraclean through my fuel system and engine and haven't had a code since. I hope your CEL stays off. Good Luck!

*Crosses fingers*
Thanks dirtyduck17, hope the same for you as well!

[Ep3 ked]

where ur ep's running in a "limp" mode when these codes where poping up?

[DRP967]

where ur ep's running in a "limp" mode when these codes where poping up?

Not for the P0420 catalyst inefficient thingy but when there was a code for "low oil level" or something like that my car was in limp mode...it would at times stop me from driving past like 70 mph or something like that.

[DA9_GSR]

I've had this issue for a few months now. As a mechanic I can assure you it's the catalytic converter and the converter only. Think like a PCM. It wants numbers. The O2 sensors feed the PCM numbers. The primary feeds the PCM a 0.9 - 0.1V fluctuation (looks like a wiggly line). The secondary O2 should give the PC a 0.45 V steady signal (it actually fluctuates a little above and a little below the 0.45 V). What's happening to you and me is the secondary is feeding the PCM the same, or close to the same numbers as the primary. Which means the catalytic isn't doing it's job. Therefore the PCM turns on the yellow "check engine" to have you get the car fixed.

Here's the fucked up part. If you bring it to Honda, they will do a run test. They will drive the car in a certain condition which should turn the light on. I duplicated this test on my car and the light never came on. Everything worked properly. Therefore, the would tell you it's a fluke that the light is coming on. They'll erase it and send you on your way only to have that bright yellow pain the ass turn right back on.

Trust me, you need a cat. You're in California and the smog laws are apparently a rear bitch over there. Up here in Canada we have smog testing, but the acceptable readings are way more forgiving than what you guys have. Replace the cat with a Honda catalytic, or buy a used on off of a wrecked EP3 with low mileage and pray to god it works out for ya.

I'm gonna be doing a K20A swap. I'm gonna buy a DC5 Type S header and cat for my smog testing and afterwards use a testpipe.

[eastsiderider]

There is a company called Random Technology that produces direct bolt-on, high flow cats for the EP. I looked into them a few years ago...and I want to say the price was around $350(back then). I just typed in a search on yahoo......and came across this place. They sell it for 399

http://yhst-43541471360993.stores.yahoo.net/02cisierateh.html

I hope this helps.

[AzNCrAzYcOoLeR]

I had this problem over the past YEAR .....replaced the CAT with a magnaflow, 02 Sensors ...still came back
last thing I did was the defouler trick. Worked like a charm. CEL never came back. omg. Should have done that from the beginning....

passed my smog check here in Ontario ..

[Ep3 ked]

I had this problem over the past YEAR .....replaced the CAT with a magnaflow, 02 Sensors ...still came back
last thing I did was the defouler trick. Worked like a charm. CEL never came back. omg. Should have done that from the beginning....

passed my smog check here in Ontario ..

I just did this trick still have CEL on after trying to clear it , no codes are showing up as well... I wish I had a clue on whats goin on :mconfused: