Its an 04 Corolla 5-spd, it has 144K miles on it, and it has had ZERO issues since new. Just tire replacement and routine maintenance. In 09, I was driving a mix of city and hwy miles and was getting about 38-39 MPG. Early this year, the gas station I use, Valero, switched to ethanol blend....up to 10%, the sticker on pumps said. I believe this was an EPA mandate? Well, I moved at about the same time the ethanol was introduced, and so I must commute 100 mi. round trip a day on week-days. So for 2010 I am now only getting 34 mpg! That is about a 13% drop! 400.00/month gas bills are killing me! Well, about 3000 miles ago the check engine light came on. I put my own OBII scanner on it, and it is giving me the code for "catalyst efficiency below minimum threshold". Its gone to being a hard/constant fault now, so after being reset, the fault dcode comes right back. I am pretty sure that with such low miles I should still have a healthy catalytic converter. I did a search on cars using ethanol blends, and found that there are quite a few cases of premature failure of cat converters after switching to E-90 or 85, and particularly in pre-2007 models.
Locally, one oil co. (forgot name) has paid off to some vehicle owners who alleged their fuel pumps were damaged by ethanol blended gas. But I have not heard of any lawsuits concerning cat converter damage.
I heard that one should have the o2 sensors checked before concluding that the cat converter has been damaged. But if I have a bad o2 sensor shouldn't the OBDII system also set a code for bad O2 sensor? I'd like to check them myself but don't have a scope, I have only a FLuke DMM that I could monitor the output signal with. I understand the one upstream is supposed to vary a lot, but the one downstream should be much steadier. SHould I forget trying to evaluate the O2 sensors myself, bite the bullet and have a pro check them out? I don't see any leaks in the exhaust system, and the exhaust itself is still like from a new car...nothing visible.
I know the other thing that will ruin a cat. converter is leaded gas. Well, no gas stations in my town have been selling leaded gas for years, it isn't even a possibility.
If indeed the o2 sensors check out and the cat converter is in fact bad, is there any way to establish that the ethanol mix caused the failure? And then is there any class-action lawsuit in the works? You can't hardly sue the EPA! I mean I am sure that to have a new cat converter installed would cost $1000 or more.
So far, the county where I live does not require any emission testing as part of inspection...but this could change. THen I would be making payments on an undriveable car, if the emissions have gone up! Advice?
First, I think the code you are pulling is for the second/downstream o2 sensor- can you post the actual code you pulled? I just had to replace mine on my 04 corolla with similar milage and I kept getting a code that I think translated to what you posted above (but was just longhand for the o2 sensor)- I just know the number that I have written down at home. Anyway, if its the code I am thinking of, it refers to the downstream o2 sensor which doesnt do a lot in our cars. Have you ever replaced that sensor, cause I think it is probably just its time- like mine. Also, the milage drop you mentioned is very similar to what I get when I use gas with ethanol- main reason I really try to avoid it and still can in CO. Thats all I know for now-
E10 did not kill your cat, E10 has been in gas for many years in most of the country. It is very difficult to find E0 now. An 11% drop in mileage is not due to E10 alone, there must be something else that caused the drop in combination with your CEL (P0420 I assume, and only one code)? Clearing that code was a good more to see if it comes back.
Do you burn any oil or have any exhaust leaks, esp around the bung? Stock exhaust? Do you use a lot of fuel injector cleaner or any oil additives? It is likely an oxygen sensor that went bad and that combined with the ethanol decreased your mileage. 144K miles is not bad for a cat or sensor to go bad, they do not last for ever and get lazy. The only way to test the sensors is back probe them and look at the waveforms, which sounds like you can.
If the cat is working the way it should, the downstream sensor will read a voltage amplitude less than the upstream one. If the sensor outputs are similar the cat is fried. http://www.aa1car.com/library/p0420_dtc.htm
I suggest getting an downstream NGK or Denso oxygen sensor and stay very far away from Bosch and any universal sensor. Clear the CEL and see if it comes back.
Really? YOu can have a bad O2 sensor , the downstream one, without getting a code for bad o2 sensor? I don't remember what the code # was, but what I said is verbatim what the OBDII scanner is translating it to, and there are no other codes. I have reset the code twice, the first time the chk eng light stayed off for a day or so, but the second time it came back on immediately. There appears to be nothing wrong with the STOCK exhaust system. All the gas stations in the area are selling E10 gas....so I don't have any choice about it. When the switch was made to E10, the price did not go down one penny, I pay more for LESS....but the corn farmers and their lobbyists in D.C. are making out like bandits.
I will replace the downstream o2 sensor and see what happens....thanks!
Really? YOu can have a bad O2 sensor , the downstream one, without getting a code for bad o2 sensor? I don't remember what the code # was, but what I said is verbatim what the OBDII scanner is translating it to, and there are no other codes. I have reset the code twice, the first time the chk eng light stayed off for a day or so, but the second time it came back on immediately. There appears to be nothing wrong with the STOCK exhaust system. All the gas stations in the area are selling E10 gas....so I don't have any choice about it. When the switch was made to E10, the price did not go down one penny, I pay more for LESS....but the corn farmers and their lobbyists in D.C. are making out like bandits.
I will replace the downstream o2 sensor and see what happens....thanks!
Yes a downstream oxygen sensor can set off a cat code and so can an exhaust leak. Hopefully you check for those before you get the sensor. I guess you dont burn oil or use gas additives or have any missfires?
If you have an IR thermometer, it should show about a 10% increase in temperature of the cat from the front to back when working correctly. If the back of the cat is cooler than the front, the cat is bad. That is about the only way to test the cat on the car. Hopefully it is just a bad sensor(s). Will you get to test them before you replace them? If the code is p0420, usually the downstream sensor is bad, but if it is another catalyst efficiency below minimum threshold code, it could be the front sensor. But it is probably best to change them one at a time.
OK, that is a great tip on checking the cat converter temp. I have an IR gun to check it. Yea, I know , I will have to run car a while so it is up to full operating temp before checking. Will see if its the P0420 code or what being set before ordering an O2 sensor. Rockauto .com has a denso brand for $55.00 but maybe autozone can beat that price. I don't have a scope to do a proper evaluation, just a Fluke DMM. As for any engine issues....it runs PERFECT, always has since I got it at 80 K miles. It doesn't burn oil, and have always used only Mobil 1 5W-30. The last oil change I added a half-qt of Lucas oil additive.
There is one issue with changing the sensors. The Haynes manual shows that the conn. for the upstream sensor is right there a short ways back from the sensor, but it says something like you have to get to the conn for the downstream one by following the cable along the 'center hump' inside the car. THis sounds like a major problem locating it, might spend hours tearing up the inside of the car to find it? Or can you just follow the cable along the hump from below and easily locate it? Thanks, Jim
My 03 Corolla has 295,000 on it and i just installed my third Catty. first one went around 180,000 and then the ( aftermarket ) replacement went around 275,000. Gas mileage went to crap and more when the light came on again, replacing the catty got me way back up there, no longer am i just feeding my car gas,
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