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I have a 2011 Golf current 12,200 miles.

I was getting excellent mileage (all long trips, little city driving) around 48 to 50 and getting better all the time.
Then I did a long trip of 800 plus miles. On the way back I had a check engine light, yellow not flashing, I called the dealer and they said it was OK to drive. As I was getting near my 10,000 oil change, I decided to wait until then to to fix it. The nearest dealer is 60 miles away. My mileage dropped to 40 mpg. The dealer replaced the oxygen sensor.

I have been driving the car and getting around 43 mpg driving carefully (55 to 65). I called the dealer about the low mileage and am taking it in next week for them to check.
They said on the phone that the oxygen sensor had nothing to do with the mileage, is this correct?

They also said that 43 mpg is normal for the Golf.

I have the records for my mileage (real, not the car computer) and they show a 47 mpg average and a high tank of 49.1 mpg before the check engine light.
What other things should I be looking for on this problem?

When I go in to the dealer on January 5, what else should I ask about?
 

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Post moved to mk6 section,welcometomyturbodies

The O2 sensor has nothing to do with direct fuel metering like in a gas car but since it controls EGR metering and the EGR metering affects intake air and how much fuel goes to that air, it could in theory affect fuel economy. I don't know for sure though, this is just a guess.

43 mpg is good. Fuel quality can vary the mpg, winter fuel has lower energy, and cold engines also take longer to warm up and which gives lower mpg.
 

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You're lucky, I'm only getting 32 mpg after 3 fill ups. I'm in Texas so I can't imagine the fuel having as much winterized additives down here. The computer mpg peaked at 36. something but I haven't gotten anything over 40 ever.

I know it's the break-in period and I'm just REALLY HOPING it gets better. Please someone post that the same thing happened to them and it's gotten better...!
 

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You're lucky, I'm only getting 32 mpg after 3 fill ups. I'm in Texas so I can't imagine the fuel having as much winterized additives down here. The computer mpg peaked at 36. something but I haven't gotten anything over 40 ever.

I know it's the break-in period and I'm just REALLY HOPING it gets better. Please someone post that the same thing happened to them and it's gotten better...!
I can't say that I'm experiencing the same thing, but I have experience drastic differences in mileage depending on temperature and the kind of driving I'm doing. Those factors will effect any car's mileage, but I've noticed that it makes a much bigger difference with a TDI.

Here are my mileage observations at about 1900 miles (3 months old).

- If running an errand includes only city streets (with plenty of stoplights), I'm lucky to get better than 25 MPG on a 2-5 mile trip. That figure goes up by a few MPG in warm weather, or if the engine is already warm when I start the trip.

-If running an errand includes a few miles on the highway or Lake Shore Drive (no stoplights, 50 MPH average traffic speed), I can usually get 30-35 MPG, depending on what proportion of the drive is slogging through traffic just to get to the highway or LSD. If I really try for mileage, I can get 41 MPG from my place on the north side to the south loop.

-A drive up to my parents house in the suburbs gets me 37 MPG pretty consistently and includes 3 miles on a busy city street with lots of stoplights and 15 miles on the highway.

-A recent 150 mile trip from Bloomington, IL to home yielded 44.4 MPG door to door with 130 miles on the interstate with the cruise control set at 78.

---All of this is on a car with less than 2000 miles. And I have a lead-footed driving style, especially in this car, as I'm rather addicted to that shove of torque at low RPM. Also, all of these observations are based on the car's onboard mileage computer, which I've found to be within 0.5 MPG of figures calculated the old-fashioned way.

Also, you might already be aware, but your car has 2 trip computers. Trip computer 1 resets every time the car is off for more than 2 hours, so it's the best one to use when evaluating individual trip MPG. Trip computer 2 only resets when you push the reset button on the dash (or maybe there's another way, but that's how I do it), so It's a good way to track mileage over 10,000 miles or so. Toggle between the 2 by hitting "OK" when in the MFI screen that displays average mileage.

What sort of driving do you do?
 

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I can't say that I'm experiencing the same thing, but I have experience drastic differences in mileage depending on temperature and the kind of driving I'm doing. Those factors will effect any car's mileage, but I've noticed that it makes a much bigger difference with a TDI.

Also, you might already be aware, but your car has 2 trip computers. Trip computer 1 resets every time the car is off for more than 2 hours, so it's the best one to use when evaluating individual trip MPG. Trip computer 2 only resets when you push the reset button on the dash (or maybe there's another way, but that's how I do it), so It's a good way to track mileage over 10,000 miles or so. Toggle between the 2 by hitting "OK" when in the MFI screen that displays average mileage.

What sort of driving do you do?
Wow, you're in Chicago and you're getting numbers like that in the past month? Impressive.

I do like to accelerate and speed on the highways. However I always try to keep my "cruising" RPMs around 2,000. Every now and then the RPMs will peak at 4,000, but that's rare and only when someone annoying in front of me is driving slow and I want to "roar" (more like meow) past them. I usually drive about the speed limit, and my morning drive to work is about 12 miles one way, with at least a third in rural/highway driving (meaning not as many lights or stop signs as city driving with speed limits around 45-55). I don't think I'm driving it so hard that it would affect my mileage by more than 2 mpg. This morning I did get consumption 1 to read 33 mpgs though, so that's not too bad for mixed city and hwy driving, higher than the EPA estimate.

It boggles my mind that some people are getting 40-50+, but they're probably driving 200 miles a day on the highway.

Yeah, I know about the consumption 1 and consumption 2 screens. It did take me awhile to figure out to click OK to toggle between the two. I kept thinking, "Why the hell does it say 1 up there? How do you get to 2??"
 

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So today my TPMS light went off. I went to the auto parts store to get a tire pressure gauge (have no clue where the old one is) and of course I walk out with a bunch of other stuff.

The door says the tires should be around 38 psi. Well the two on the left side were at 40 and the front right tire was around 36. The rear right tire was 28. 28!!! So I inflated the two on the right to around 39-40ish.

Anyone think that's overinflated?

I wonder why I lost so much air pressure. And I also wonder why the light didn't automatically shut off (I had to reset it via the glovebox). Hopefully this will help my mileage - maybe it dropped awhile ago but something recently dropped it out of the +/-5 psi threshold.
 

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Obviously your sticker is on the door well in the UK its on the fuel filler flap. I would stick to the recommended pressures. With TMPS it will be activated with a 3psi drop in any tyre so they are quite sensitive. After you have readjusted the tyre pressures you need to press the Set button which is in the glovebox on mine so it will recalibrate. ;)
 

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40 is perfectly fine, esp in the winter. Although that might not be a factor in TX.
Yeah, I thought the same (about being in Texas that is) but late tonight I'm going to depart for New Mexico. Now it's not snowing or anything like that up there right now, but the low will be around 22, at least 10-15 degrees cooler than our low, if not 20 degrees. The weather here lately has been highs of 74 and lows ranging from 35-55, so it's basically switching between warm, short-sleeve weather to bundle up weather.

Obviously your sticker is on the door well in the UK its on the fuel filler flap. I would stick to the recommended pressures. With TMPS it will be activated with a 3psi drop in any tyre so they are quite sensitive. After you have readjusted the tyre pressures you need to press the Set button which is in the glovebox on mine so it will recalibrate. ;)
I thought I was told that whenever you hit the reset button in the glove box it recalibrates your +/- setting. Is it at +/-3 psi? I thought it was at 5, but a smaller number would make sense.

For instance, if it was calibrated at 38 then it would go off at 35 (or lower) or 41 (or higher). If you readjusted your tires to, say 39 psi, then it would activate at 42+ psi or 36 (and lower) psi. Or does it always just reset to 38??

Also, is it normal for the TPMS to automatically shut off if you fill up the right tire? Because mine didn't do that yesterday.
 

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Also, is it normal for the TPMS to automatically shut off if you fill up the right tire? Because mine didn't do that yesterday.
Right tires yes, left tires no :p

I'm not sure but I think it should. I know it does take a while for the system to start working again after you reset it so maybe that was why. Not sure.
 

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Now there are different TPMS systems, Indirect and Direct, mine is the Indirect.

With mine the TPMS doesn't automatically shut off thats why you have to press the Set button in the glovebox after you have changed pressures just to calibrate it again.

Fitting a direct Tyre Pressure Management System (TPMS) ;)
So after a 1500 mile round trip, I averaged between 35-41 mpg. Now it was in the mid teens to mid 30s during the drive there and back, and the increase in elevation (from East Texas to Albuquerque, NM) probably had an effect, not to mention the 75 mph speed limit in NM. My MFI showed 42.2 mpg as the best for the trip on the way back. I was also using Diesel Kleen in the white bottle.

Of course the TPMS came back on today and all the tires were fine... except the back rear tire. It was again, at 28 psi. Should I just take it to a dealership and have them look at it? I could understand if all of the tires were a little under pressure since they might need to get "broken into" or whatever, but it's just one tire.
 
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