Sudden loss of MPG

[Penaran561]

I recently noticed that my miles per gallon have dramatically dropped. A few days ago I had a check engine light, it came up as P2201. So would a NOx sensor have anything to do with low MPGs? I have checked out some posts on how to get better mileage such as drive with the AC off, drive in 6th gear on the manual setting on the DSG. If it helps I recently put new tires on it about 1.5k miles ago didn't notice MPG drop though, and changed air and fuel filter 1k miles ago. I went from 38-42 on highway to a low 28-36. Thanks!

 

[c-wagen]

...A few days ago I had a check engine light, it came up as P2201. So would a NOx sensor have anything to do with low MPGs? ... Thanks!

Amount of fuel is related with NOx. In a gasser at some point more fuel for the same amount of air will reduce piston combustion temperature, not burning completely, but vaporizing and absorbing some of the combustion heat. Im not sure if in a diesel is the same, but the signal from the NOx sensor might be required to tune the amount of fuel, and the lack of signal can increase fuel consumption (ECU will need to assume something, and operate the engine less efficiently). Have it fixed, your mileage might go back to normal (or leave it as is and have Vw buy it back from you).

 

[Penaran561]

Looks like I'll have to fix it. I don't plan on returning my car it just seems a little over priced for that sensor... Thanks for the response!

 

[VeeDubTDI]

P2201 shouldn't be causing low fuel economy, IMO. Here is a thread discussing it a little bit more: http://forums.tdiclub.com/showthread.php?t=367393

How are you determining that your fuel economy is worse than it used to be? How many tanks have you noticed this on, are you hand calculating, etc.?

 

[Penaran561]

I'm on my second tank since I've noticed this. I'm hand calculating. I barely got 500 miles out of my last tank, usually I'm at 590-630 miles per tank. Right now I'm at 205 miles driven and one tick mark from half tank.

 

[nord]

Just some basics...

Brake(s) dragging? Bad wheel bearing? Have you changed both the fuel and air filter? Is your in-tank lift pump working?

I ask these things because none are really monitored by your ECU. I'd place filters at the top of the list as changing them is the first rule of diesel. Once your air filter has been changed, then I'd suggest checking your mileage once again. If still sub-par, then disconnect your MAF and see what happens.

Obviously you could have a mechanical problem which would remain unknown to me, but I suspect not the case. Either something is causing rolling resistance or you have a fueling or air problem. While it makes very little sense, a dirty fuel filter will actually present itself in the manner you describe.

Good luck and look for the simple things. Usually it's something small which presents itself as a serious problem and really isn't.