DumpdEJ6

1999 Civic Hatchback DX

All stock D16Y7

I drove the car from Maryland to North Carolina, no CEL. Replaced ISB, Countershaft Bearing, Clutch, Rear Main Seal, Power Steering Rack and Pinion, Timing Belt/Water Pump/Tensioner Pulley, tune up with OEM cap and rotor, NGK plugs, K&N air and oil filter, Mobil1 High Mileage Synthetic.

Then I did the Seafoam 1/3 in the tank, 1/3 in the crank, (before I changed the old oil!) and 1/3 through the brake booster line. I cut the car off after feeding the last 1/3 into the hose and let it sit for about 20 minutes to allow the Seafoam to soften the carbon deposits. Turned it back on, held the RPMs around 4K for a minute or so, then went on a "spirited drive" to clear out the rest of the Seafoam.

Now, however, the CEL is on for O2 sensor bank 1 and bank 2, which to my thinking means that it's either both sensors have gone bad all of a sudden, or I burned up my catalytic converter, which is the type that is integral to the exhaust manifold. I initially thought I perhaps switched the plugs up after having them disconnected 4-5 times due to all the other work, but after clearing the codes and switching plugs, 20 miles later they came back.

Did I mess up my catalytic converter or my O2 sensors from the Seafoam? Its the only thing I can think of that I did that could have effected them. Has this happened to anyone else? I'd rather not throw parts at it considering the cost of the O2 sensors, not to mention the cat.

HondaPartsHero

Is the car running bad? What codes specifically is it throwing?

Rusty94cx

Pull out 02 and see if it is there and or melted. Should have possibly removed the 02 prior to seafoam. To late now.

DumpdEJ6

I should add that the codes were technically not for O2 sensors, they were "catalytic converter below efficiency threshold Bank 1 and Bank 2".

HondaPartsHero

What are the Pxxxx codes?

Former User

This^

Post the specific OBD2 code. Is it P0420?

DumpdEJ6

It is P0420.

DumpdEJ6

Also the car doesn't seem to be running any appreciably worse...or really any better, for that matter. But occasionally it will idle low after warming up, like around 400 RPM low. I notice it happening maybe 20% of the times I'm sitting at a light. I can't detect any misfiring and it always runs smooth while driving.

saefifty

Clear the codes.The CEL light comes on when u decarbon it probably won't come back on

DumpdEJ6

No I did clear the codes, they came back on.

Former User

How much have you driven the car since doing the Seafoam treatment?

DumpdEJ6

Approx. 200 miles. I would say it came on maybe 50 miles in, then I cleared the codes, then it came on after another 30 or so, and then I cleared the codes and switched o2 plugs, then it came on after maybe 20-30, then I switched the plugs again and have just driven it with the CEL on for the rest of the time.

Former User

Why are you switching O2 sensor plugs?

Do you pull the code every time to ensure that it is P0420?

Have you checked for an exhaust leak? That can also throw P0420.

You also might want to try removing and cleaning the O2 sensors.

DumpdEJ6

I switched the o2 plugs because I (mistakenly) thought I could possibly have connected them to the wrong sensors after having disconnected them several times doing all the other work to the car. They DO have the same plugs on them, and I thought "well, its a long shot, but maaaybe..."

I did not pull the code the second or third time. I know I should have but it there has been nothing else wrong with the car and, while sloppy diagnosing work on my part, I still feel there is little chance of it being something else. But I will clear the codes again tonight and check the codes when they pop up again.

I DO have an exhaust leak, but it is after the cat and shouldn't effect anything. Also, the exhaust hasn't changed since the drive down from Maryland, and I would think if it was going to throw a code for a leak it would have thrown it then.

What would you recommend to clean the o2 sensors with?

Former User

Are you sure that the O2 sensors are now connected in the proper order? This is done by matching the wire colors in the connector to the sensor.

Brake cleaner should work fine to clean the O2 sensors.

DumpdEJ6

I am sure. For one thing, when I switched them, I noticed that there was very little slack in the wires on one, and lots of slack in the other. So I pretty much knew I didn't accidentally switch them before, but I still had to try, just in case. Hopefully I didn't do any damage to them by switching them on purpose.

I will try clearing the code and cleaning them in the morning, then drive to work and see how things go. Thank you very much for your help, you're such an asset to these boards.

MikesEJ1

If you have P0420 your catalytic converter is toast....Try removing the cat and looking inside to see cracks in the catalyst or if it looks sunken in
This code is not for O2 sensors

KaburaGarage

iTrader: (2)

You may have fried the cat.

Tony_SS

I have the factory manifold / cat that I just took off mine.. no cracks or codes with it.. PM me if you want it.

sleepyaccord96

i have never ever pulled seafoam thru the hose and turn it off and let it sit. You can hydro lock an engine and or bend a rod or 2 or 3 doing that. engine should have stayed running while doing that in order to burn it off quickly. Good luck with it but it sounds like you may have damaged the cat doing the seafoam which is possible but i have yet to see seafoam do that to a cat.

DumpdEJ6

Well a bit of an update: I pulled the codes this morning and got 3 codes, p0420, p0430, and dammit I forget what the other one was but it was "Catalytic system efficiency below threshold". After googling that, it seems like another p0420 code, that's a little confusing.

Anyway, I expected the codes to show up since I switched o2 sensor plugs yesterday. So this morning before work I cleared the codes, pulled the pre-cat o2 sensor and cleaned it well with brake cleaner. I didn't have time to get to the post-cat sensor or I would be late for work, so I put the cleaned sensor back in and drove to work, tripped the odometer and it was about 32 miles of mostly highway speeds. No CEL.

Once I get out of work, I pull the post-cat sensor and clean it thoroughly as well, then drive home, another 32 miles. At this point there is still no CEL, although I was expecting it to pop up any second, lol. After I get home, I head to the gym, about a 5 mile round trip, city driving, still no CEL.

Hopefully it stays that way, but I'm still not getting my hopes up, seems too easy. Knocking on wood right now, we shall see. I will update tomorrow after another round trip to work, if it's going to come on, it should by then.

Thanks for the help everyone!

DumpdEJ6

Welp, here's the update: 5 miles into my drive this morning the CEL came on. After I got off work I checked the codes, two P0420's and one P0430. I ran the data collection on the car with it running and the first o2 sensor fluctuated constantly from .0250 - .0800 and the second o2 sensor remained at a steady .015 which leads me to believe that not only are both sensors working, but it seems the catalytic converter is ALSO working, since it's knocking the fluctuating fuel levels down to a low, constant level.

Am I correct here? Why are these codes being thrown?

MikesEJ1

dude if you have these codes you need a catalytic converter....end of story

get a new cat/exhaust manifold,replace it,and then go from there

DumpdEJ6

I'm going to take the scan tool and go for a highway drive where I can modulate the throttle and take readings at something other than idle, perhaps that is where either the cat or the o2 sensors will show their true colors. I'll report back tomorrow with my findings, good or bad.

94EG8

You'll start getting catalytic converter codes once the converter drops below about 95% efficiency from what I've heard.