boyguan

I would take the cat off and take a look at the honey comb. But most likely it will be fine since it passes out of the pipe

90 percent o2 sensor. Looking is free which is why I suggest that

My cat had one of the honey combs come loose and hit the o2 sensor flattening it and rattling. Just a FYI

Reckon

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

So, more than likely, your first sensor is broken. Might as well replace both while you are at it. This is something you can do, but if you don't feel you have the tools or skills, see if you can get some local guys to help out. Otherwise, your best bet is to work with the mechanic to replace the sensors.

MR.T

I'm pretty sure you'd be throwing more O2 related dtc's if your O2's were toast... Especially if one had broken off. If It did happen to break or get damaged as reckon suggested I X2 on replacing both sensors. I've always thought of them like shocks or spark plugs, if one goes out the others are probably close behind.

There's a good chance that yoru cat is clogged or broken and in some cases a visual inspection tells you nothing, but can't hurt to take a look. New cat gaskets, if I remember correctly, will run about 20-30$.

How long did you ride around with this code? Did you by chance have other codes, like misfire or O2 codes that you kept driving on. If so, That will destroy a cat in no time.

Regardless, don't start talking about parting it out over such an easy and cheap fix. It's really not that big of a problem.

icecreamballer

The CEL had come on and off for couple of years. At first it was the fuel cap that was the problem so I replaced the fuel cap. and then last year, around thanksgiving, I had engine misfire so I had to replace ignition coil and injectors and few other things. And the CEL came on again and I always thought it was the fuel cap again. And i read somewhere that fuel neck could have been deformed since my fuel cap is new. So I drove around with CEL on for a while since the CEL turn off every once in a while. So I didn't think much of the CEL, thinking it'll be okay as long as I close the fuel cap right.

However, since this year thanksgiving, the engine is starting to feel little shaky at idle again. It feels like maybe I'm gonna have misfire again like last thanksgiving.

The plan is to go get the o2 sensors replaced tomorrow and see if it is the o2 sensors.

I'm hoping that my cat is not damaged... Could it be damaged still if my emission results were all good?

MR.T

yeah good point, didn't really think about that. i have heard of people with no cat at all passing emissions/smog in these cars. we use 93 octane, so that'll burn a lot cleaner.

you're at 200k and probably on the stock O2 sensors, so it's probably not a bad idea to put new ones in, but a used cat and gaskets would maybe be a bit cheaper than O2's. i bought my cat off of this forum for 80$..

i do my own work, so i know my scenario is a bit different, but if it were me i'd...

first inspect both O2's for visible damage and if none,

then remove cat and inspect for visible damage.

if none there, i would test the O2's with a voltage meter. looking for signs of a lazy or dead O2.

if that panned out, i would then test pressures across the cat. if your cat is partially clogged that's make your car run like crap for sure. and if you rode for awhile on a misfiring engine, there's a good chance that you've damaged/clogged the cat.

on a side note, if you do start having misfire s again, check the valve spring retainers for cracks. there's info here https://www.s2ki.com/s2000/topic/805...#entry19232395

davidc1

Couple of observations....

Get a new mechanic. He does not have your best interests in mind. The fact that he doesn't offer to replace the O2 sensors with aftermarket OE ones for $50 or less each means he doesn't give a crap about you. Find another mechanic.

Unless smog laws changed this year, I don't think the DMV has anything "stored" about your car.

Your smog guy sounds like he's trying to be helpful as well, but he's a douchebag for even hooking your car up with the CEL on in the first place. He should have told you to get whatever the problem is fixed before he went through the testing process.

You can't have an autoparts shop test for you, or lend you an OBD code reader in CA. Haven't been able to for years now.

S2k cats have a know issue with the core breaking loose and chopping off the nose of the downstream cat and causing a CEL. This will not affect drivability or smog. Usually the cat will rattle.

If it passed smog, the cat is probably functioning, even if the core is broken.

93 Octane doesn't burn any cleaner. Another common misconception about what octane is in the first place.

Burning a quart in 1000 mi is normal.

The vibration could be an engine mount gone bad. You've got 200k on the car.

You said the code is for the upstream O2 sensor. Easily could be bad at 200k.

There is only one company that makes a CA CARB legal cat for our car. They've only been doing it for a couple of years. I think it's Flowmaster. But, it's not a real high flow cat like ours, so you would probably loose power.

You smog mechanic will not know if replacing the 02 sensor solves the CEL until after all the systems reset themselves (can't remember the name for it, duh...). This could take 40-120miles of driving. Usually the 02 sensor one is the last to reset.

It is illegal to sell a used cat in CA. But, you can find used ones on the various boards for about $60-120.

If you want to work on your car a little you can save some money. Replacing the 02 sensors is probably one of the simplest things to do after changing your fluids. Both 02 sensor are easily visible. Occassionally one will sieze and be hard to remove. An guy who's changed them before could probably jack up the car and change both in less than a half hr. If you've never done it before, count on a couple hrs if one siezes. There are several DIY threads on the forum.

You're smog guy is ripping you off on the pricing as well. I'm not sure what Mitchell says is the book rate on it, but I wouldn't think its rated at more than 1hr each. So, $500 for both is a lot of money.

Buy the replacement sensors at oxygensensors.com like the other guy suggested. I've boought many from these guys. They are local to me so I go there and pick them up. But it's usually free shipping I think. These are OEM sensors. The OE sensors Honda sells are just one of those things were the dealer part costs a princely sum for no apparent reason. You mechanic should have realzed this. Find another mechanic. Seriously. Where in CA are you?

MR.T

Davidc1, I agree totally with what you are saying. Although I'm almost sure that's if his O2's were bad or broken he would have thrown an O2 related dtc such as a P0141 circuit malfunction or low voltage, or something. Usually if an O2 is bad it'll trigger a code, then if you run on it for too long the P0420 will eventually follow.


I was told my whole life that 93 burns cleaner and was better for the environment, so if that's not true I stand corrected. Personally I've never done any research into that area beyond what I was told.

icecreamballer

I am located in Los Angeles area and my smog shop is in Pasadena. My mechanic is in Glendale. And I work in Orange County.

This morning I took my car to the smog shop and he will charge me $80 for swapping out o2 sensors and figuring out if o2 sensor is the problem. If it turns out that o2 sensor is not the problem I don't need to pay him $80.

So basically he will change the o2 sensor and drive it around. I'll pick up the car tomorrow morning and drive it some more and see if CEL comes back on. If it doesn't, then the conclusion would be that o2 sensors need to be replaced. If that is the case he will charge me around $200 for new sensors and $80 for labor. But I have the option of buying the sensors myself and give to him to install and just pay $80 labor. since it looks like it's possible to buy the sensors for less than $200 based on the info you guys have provided.

Does this sound like a good plan? I wish I had the time and tool and garage to change the sensor myself but unfortunately don't have any of that.

davidc1

that sounds like a really good plan. Your mechanic sounds like he's being fair. Buy your own o2 sensors as well. Or just have him order them from the same place. Since you work in Orange County there's a good s2000 specialist there. His name is Alex, and he owns a place called Ballade Sports. You can google him for his website.

davidc1

I agree with your regarding the codes. I didn't really pay attention to exactly what code he mentioned his car showed.

Regarding octane...in my 52 years on this planet, I've seen many, many misconceptions and misinformation out there on many subjects regarding cars. Perhaps the two most common ever are what octane ratings really mean, and various things regarding motor oil. So, your idea of what octane is and means is not uncommon.

All other factors being equal, all octane ratings really mean is the gasolines ability to resist detonation. Absolutely nothing else. Doesn't burn cleaner, doesn't give more power, doesn't improve gas mileage, etc.

Having said that, modern engines can be designed to give better mileage and give more power by using higher octane gas, but the octane rating itself doesn't do this.

From Exxon's website:

Why should I use your premium gasoline (91-93 octane) instead of regular (87) or midgrade (89)?To find out what octane your engine needs, first check your owner's manual. The recommended level is often 87 octane. Some models have high compression engines which are designed to utilize the octane levels of 89, 91 or higher.Ordinarily, your vehicle will not benefit from using a higher octane than is recommended in the owner's manualMost vehicles do not benefit from a higher octane level than what is recommended but using a lower octane than recommended can cause engine knocking or pinging in some cars.

From wiki:

Octane rating or octane number is a standard measure of the performance of a motor or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating. In broad terms, fuels with a higher octane rating are used in high-compression engines that generally have higher performance. In contrast, fuels with lower octane numbers (but higher cetane numbers) are ideal for diesel engines. Use of gasoline with lower octane numbers may lead to the problem of engine knocking.[sup][1][/sup]