p0420 and ethanol?

[yippeekyaa]

Here is the situation. For the last 3 years in august i've taken a trip from my home in NC to the FLA keys for vacation. Every year the same thing happens. I get to SC fill up with ethanol and within 30 miles the check engine light comes on. It stays on the entire trip until i get back into my home state and fill up with a NON ethanol blend. 30 mintues after the Non ethanol fill up the light goes off. Each year when this happens i would stop at an advance auto and confirm that it was the p0420 code. I havnt replaced the cat yet, still running the original cat that came on the car.As a side note my 03 vibe gt normally gets @ 360 miles on a tank. But with the ethanol it barely gets 300 between tanks. Is that lower mpg due to the ethanol, the check engine light or both?I'm proposing a theory here that the numerous postings here about the p0420 code and bad cats are false. I think its more of an issue with the ethanol blends and not the cats. Discuss.

[kevera]

Do you know how much ethanol is in the fuel.Up hear it's 5%.Every gas station where I am has a blend and I haven't got a code for that yet.

[hskater26]

i posted this in another thread but i just go this code again i just replaced my cat about 6months ago when it came on....

[hskater26]

and i think here in RI and mass its 10% ethanol

[northvibe]

yeah MN has a 10% blend i thought and I never threw a cel in the vibe or ms3....hmmm more reseach on their gas may be needed.

[DavidPIL]

I'm interested in this topic as well...Locally, I had stayed away from Mobil because the pumps say up to 10% ethanol. I always went to the Marathon places because they didn't have the sticker and assumed they didn't. When I went to Mobil before thinking about the ethanol, I would noticeably get a reduction in MPG of 3-5 per gallon. Now it seems I'm down 2-4 per gal from where I used to be no matter where I go.I used to get my best mileage when visiting Myrtle Beach every August though twice on the trip down I fueled up at an Exxon North of Columbia which caused the engine to become very loud and also made me lose several mpg. That always cleared up after refueling (and dropping in a bottle of Techron or Redline's fuel additive.I never got the dreaded P0420 from it though but I have to wonder if I was on the verge of it. Ethanol is evil!

[yippeekyaa]

David, that is the kind of information im looking for. by Columbia did you mean columbia SC? I ask this for two reasons. First it seems odd to me that you would travel through Columbia SC to get the Myrtle Beach from Ill. Secondly, Columbia area is where i get my first tank on my trip to the keys and is where i get the cel every year for last 3 years. Its also great information in that we have the same year and make of vibe.edit: nvm on the Columbia question, just ran mapquest on your route. makes sense to me now.

[yippeekyaa]

hskater26, when you replaced the cat 6 months ago, exactly which cat did you replace it with? Factory, magnaflow, etc. Did the stealership do the install? If so did they reflash the PCM as per the bad cat TSB?

[DavidPIL]

I would say no more than 20 miles North of Columbia on I-26... Was a newer Exxon on the West side of the Highway. And yeah, Columbia is slightly out of the way but not that bad. The last time I went down, I took NC-74 through Charlotte then took back roads to Myrtle Beach. That way adds more time but is much shorter in miles.I've often wondered if there was some type of test strip to verify Octane. I really thought the place put Reg in the Premium tank so my engine adjusted which caused the engine to become more loud. I also have to wonder sometimes if it's not so much ethanol in my other cases of a lowered mpg as much as it's them selling the wrong grade of fuel as Premium. Could that actually throw the P0420 cel too?

[SkyVibe]

yippeekyaa- are you sure you didn't fill up with E85? It is sold at a number of stations around Columbia and is NOT for non-flex fuel vehicles.

[hskater26]

Quote, originally posted by yippeekyaa »hskater26, when you replaced the cat 6 months ago, exactly which cat did you replace it with? Factory, magnaflow, etc. Did the stealership do the install? If so did they reflash the PCM as per the bad cat TSB?im pretty sure its stock......the mechanic i bring my car did the install for me

[northvibe]

yippeekyaa - did you have your cat replaced under the tsb? I remember most 03 gt's had their cat's fail, maybe you just have a half failing cat that wont fully die

[breezd]

Here in southeast wisconsin, the ethanol blend is up to 10%. But when you get about an hour away from here, they do not have the ethanol in the gas. I always try to fill up when I go outta town because I feel that the non-ethanol blend gas is a lot better...

[yippeekyaa]

Skyvibe, I'm 100% certain i filled up with 10% ethanol blend. Sticker on the dispensor said "may contain yada yada" and a seperate island with E85 clearly marked. Plus i dealt with 10% ethanol for the next 3 fill ups and 1100 miles of travel with the CEl on. Returned to home state, filled up with usual non ethanol blend. 30 minutes later light goes off. 3 years straight now on nearly identical trips.northvibe, I'm out of range milage wise for the tsb replacement. But i did have the stealership flash the pcm with the new codes 3 years ago when i first got the cel. Car still has the original factory cat.

[SkyVibe]

I'm curious how you know for sure your fuel in NC has no ethanol? I just researched it and NC does NOT require stations to label that they have ethanol. SC does. An article I read claims 50% of NC stations now have ethanol in their gas. In any case it is a very strange situation you are having, the ethanol shouldn't cause a check engine light.

[yippeekyaa]

Yes it's true that labeling of 10% blend is not required here. But, it's very east to tell which stations are using it. The no-name brands that are usually 5 to 10 cents cheaper per gal use ethanol as a general rule. I use the same brand as much as posible and im 100% certain that they do not use ethanol. My brother in law drives a delivery truck for them. On a side note, the fuel shortage due to Ike forced my wife to fill up at the only station that had gas last week when she needed it. It was a station i know uses ethanol and guess what. The cel light came on, Advance auto verified the p0420 code yet again. When my regular source was restocked i took 4 5 gal gas cans and filled up before they ran out again as wife had the car at work. 2 days after putting that in the car the light went out, go figure. To add insult to injury im debating this whole ethanol thread i created. Maybe there is something wrong with my car. A borderline oxy sensor? A cat that as someone else mentioned may be partially dead so that only ethanol triggers the light? So in that light i ordered 2 new oxy sensors to replace the original ones (140k miles). After a couple of tanks ill put some ethanol in and see what happens.

[SkyVibe]

Maybe the sensors will fix it...Keep us posted as I'm very curious about it. I hate ethanol/gas and have managed to find a few stations around Columbia that don't have it and I make a point of buying gas there in cans for my non-auto equipment, ie boat motor, lawn mower, atv, motorcycle etc. Ethanol gas doesn't store well so I like the plain stuff for motors that sit sometimes for awhile. Unfortunately it is impractical for me to seek it out for the wife's car and I drive a diesel pickup when not driving a company car

[Pack52]

I could swear this just happened to me in NC as well. Filled up at a discount "may contain 10% ethanol" station, and got the P0420. Stayed on throughout the tank. Filled up again after reading this thread at a BP, light gone within 30 minutes. Will see if this happens again and repost...