I know just enough about my car to be slightly dangerous/useful but clearly not enough to have a confident answer to this question.
I have a 2005 Corolla CE with about 77k miles. In town mileage has dropped to about 22-23 mpg now that the colder weather is back but highway is still around 35mpg. This also happened last winter and recovered slightly during the summer months. It's not throwing any codes so I had someone take a look at it and they believe it might be an issue with the A/F ratio sensor in the neighborhood of a P0171 code.
My questions are these:
1. Where the heck is the A/F ratio sensor? I've read some stuff indicating that it might actually be the upstream(?) O2 sensor and can't find it's location in my Chilton book.
2. I originally bought the car in southern California so would I need to find a replacement part that is CA vehicle friendly?
You have an Oxygen Sensor, not an air fuel ratio Sensor and it is located right in the manifold. should be right on top and not hard to spot.
secondly, there isn't a differentiation between CA and non CA car, but if there were, I'd say yes go with the CA spec one.
hope this helps
It does help!
I'm just confused because it looks like there is such a thing as a A/F ratio sensor replacement part (by Bosch) but that is actually an o2 sensor, yes?
The upstream O2 sensor on the 2005+ corollas is actually an air fuel ratio sensor, it is a type of oxygen sensor. This sensor has a more of a direct impact on MPG than the downstream O2 sensor. You will also see that it is very expensive to replace. Also from reading, Bosch is not the way to go on Toyotas, stick with NTK or Denso direct fit, skip the universal sensors. If you do decide to get the sensor, you will have to remove the heat shield and soak the sensor with some penetrating oil as the exhaust heat tends to "weld" the threads to the bung and use a 6 pt box end wrench to remove the sensor. With 77K miles, I doubt this will fix your issue though.
Also, if you warm your car up in the winter for longer than a minute, that may explain a drop in mileage beside winter gas and the cold weather. Warming up the car hurts your mileage.
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The upstream O2 sensor on the 2005+ corollas is actually an air fuel ratio sensor, it is a type of oxygen sensor. This sensor has a more of a direct impact on MPG than the downstream O2 sensor. You will also see that it is very expensive to replace. Also from reading, Bosch is not the way to go on Toyotas, stick with NTK or Denso direct fit, skip the universal sensors. If you do decide to get the sensor, you will have to remove the heat shield and soak the sensor with some penetrating oil as the exhaust heat tends to "weld" the threads to the bung and use a 6 pt box end wrench to remove the sensor. With 77K miles, I doubt this will fix your issue though.
Ok I'm starting to catch on. So this is the sensor up top in the exhaust manifold? Also, you mention that it's expensive to replace. Is that because an upstream specific O2 sensor costs more than a universal sensor? Sorry for asking some probably obvious questions. I'd always rather go in to a shop armed with some information and not just a blank stare and a credit card.
Is there a different approach I should be taking? AT 77k miles is this something I should just accept? My '89 Corolla was getting 30-35 in town until the end but obviously the guts are different.
Ok I'm starting to catch on. So this is the sensor up top in the exhaust manifold? Also, you mention that it's expensive to replace. Is that because an upstream specific O2 sensor costs more than a universal sensor? Sorry for asking some probably obvious questions. I'd always rather go in to a shop armed with some information and not just a blank stare and a credit card.
Is there a different approach I should be taking? AT 77k miles is this something I should just accept? My '89 Corolla was getting 30-35 in town until the end but obviously the guts are different.
Yes, it is located in the exhaust manifold. It is just expensive because it is a A/F ratio sensor. Expect to pay $190 for that sensor if you go to the dealer. Not sure what else you could look at. How long do you warm it up?
Yes, it is located in the exhaust manifold. It is just expensive because it is a A/F ratio sensor. Expect to pay $190 for that sensor if you go to the dealer. Not sure what else you could look at. How long do you warm it up?
It looks like I can get a Denso for $100-$120 online. With the slotted socket adapter, is this something I could tackle myself?
In the morning, I usually only warm it up long enough to defrost/defog my windows. Maybe 1-2 minutes at most. The rest of the time I don't warm it up at all.
It looks like I can get a Denso for $100-$120 online. With the slotted socket adapter, is this something I could tackle myself?
In the morning, I usually only warm it up long enough to defrost/defog my windows. Maybe 1-2 minutes at most. The rest of the time I don't warm it up at all.
First of all, to TN.
IMO the drop in mpg could easily be due to the combination of warming your car up for that long & the winter gas change. Don't warm up the car, just start it & drive easy until warmed up. This will burn off any condensation quicker & give better mileage. Plus in our area it doesn't get cold enough on average to worry about warming up the car.
If you are not throwing a code than I wouldn't waste any money on the Bosch part. I just had the same thing happen with my 94 Corolla but my overall mpg's dropped to 22 mpg. I changed the O2 sensor with new plugs & overall mpg went back up to the normal 32 mpg per tank.
__________________ 89 Supercharged White MR2 5-speed / 09 Corolla S CSM 5-speed
07 Matrix XR Gray Pearl 5-speed (sold 11/23/11)/ 94 Corolla DX Red 5-speed / 95 Previa S/C White Auto/
07 Corolla CE CSM 5-speed/ 10 Prius III Blizzard Pearl
IMO the drop in mpg could easily be due to the combination of warming your car up for that long & the winter gas change. Don't warm up the car, just start it & drive easy until warmed up. This will burn off any condensation quicker & give better mileage. Plus in our area it doesn't get cold enough on average to worry about warming up the car.
If you are not throwing a code than I wouldn't waste any money on the Bosch part. I just had the same thing happen with my 94 Corolla but my overall mpg's dropped to 22 mpg. I changed the O2 sensor with new plugs & overall mpg went back up to the normal 32 mpg per tank.
LOL I know it's not like we live in the arctic but I park in a dark, tight lot and the last thing I need to do is back in 6 cars on my way out. Will try to give my windows a good wipedown and hope for the best. Plugs were done in February so it looks like changing the upstream sensor is in my future. Should I also do the downstream while I'm at it?
LOL I know it's not like we live in the arctic but I park in a dark, tight lot and the last thing I need to do is back in 6 cars on my way out. Will try to give my windows a good wipedown and hope for the best. Plugs were done in February so it looks like changing the upstream sensor is in my future. Should I also do the downstream while I'm at it?
Wiping the windows fist just to back up will work or back in at night so you can pull straight out. Just change the upstream unit if you really want to but if you aren't throwing codes I would leave it alone & see what this does for you first. I would also look at the plugs & see if things look okay. The fact that you are getting good hwy mpg that tells me that things are okay. If & when you do change the O2 sensor, get a Toyota part, not a Bosch, you will just be wasting your money.
__________________ 89 Supercharged White MR2 5-speed / 09 Corolla S CSM 5-speed
07 Matrix XR Gray Pearl 5-speed (sold 11/23/11)/ 94 Corolla DX Red 5-speed / 95 Previa S/C White Auto/
07 Corolla CE CSM 5-speed/ 10 Prius III Blizzard Pearl
You mentioned a P0171. You know it has nothing to do with AF sensors, right? It's a fuel system lean code. No it's not a fuel pump or filter. Try cleaning out the Mass Air Flow sensor, don't use carb cleaner, you can buy MAF cleaner. Simply put, if the system thinks its lean, it gives it more gas to account for it. Dirt or lint from the air filter can build up on the filiment and cause the sensor to give a false reading. Colder more dense air could effect that reading. Ive seen them do this and not trigger a dtc. Replacing the AF sensor is killing the messenger. Beyond that a vacuum leak could also cause it.
I know just enough about my car to be slightly dangerous/useful but clearly not enough to have a confident answer to this question.
I have a 2005 Corolla CE with about 77k miles. In town mileage has dropped to about 22-23 mpg now that the colder weather is back but highway is still around 35mpg. This also happened last winter and recovered slightly during the summer months. It's not throwing any codes so I had someone take a look at it and they believe it might be an issue with the A/F ratio sensor in the neighborhood of a P0171 code.
My questions are these:
1. Where the heck is the A/F ratio sensor? I've read some stuff indicating that it might actually be the upstream(?) O2 sensor and can't find it's location in my Chilton book.
2. I originally bought the car in southern California so would I need to find a replacement part that is CA vehicle friendly?
Thanks for any help you can give me!
Sorry this seemed like he was saying something about a code, this is a common error.
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Sylvia
Plus in our area it doesn't get cold enough on average to worry about warming up the car. 
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