Yaris Mileage Has Suddenly "Tanked"



My Yaris is now a year old. It has been getting a very consistent 36 mpg–up until about a month ago. All of a sudden, I had a 32 mpg tank, and since then it’s been 33-35 mpg. What could have caused my mileage to go down all of a sudden? I just took it in for its 15,000-mile service (forgot to ask them, but I’ll call them if necessary). I’ve been doing exactly the same kind of driving I always do, and the gas has come from the same stations (I fill up at Wal-Mart and Texaco).


Is it a manual or automatic? Has the CEL come on? How long have the spark plugs and wires been on the car? Have you noticed any derivability changes or unusual noises?

I would suggest checking tyre pressure (inflate to the pressure indicated on the sticker (glove box or fuel cover) or the owner’s manual and checking to see of there are any stored error codes (you may have some even if you have not noticed the CEL (Check Engine Light).


It’s a manual; I’m the original owner. I’ve had it serviced regularly since I’ve owned it.

The first occurrence of this was right before the 15,000-mile service. It did not improve (or not by much) after the service, at which time they would have inflated the tires, checked for any problems, error codes, etc.


I would check the mileage over a few fillups before becoming concerned. +/- 4 MPG is pretty much within reason especially with the inaccuracies of fillup(when pump stops) and the trip odometer etc.


Check your front end alignment in the year that you put the 15k on it? How about tire pressure? The 4 mpg is about 10%, which is not pointing to engine (to me anyway) problems. I’d check the alignment and pressure, maybe change the air filter, and pay attention to my driving style. Stop lights, excessive idle time, warm-up, a/c use . . . all can contribute to less mpg. Good luck! Rocketman


I understand that, and I have accounted for it. It’s just that until now, EVERY SINGLE TIME it’s been right at 36.X; then it was 32, 34, 36, 35, 32, 33–like that. Since I’ve owned it for a year and I fill up once a week, it was very noticeable.


The just did the alignment, tire pressure, etc. at the 15,000-mile service (and, I assume, the filter, although I need to check that to be sure–service was done at the dealership). My driving has not changed; where I fill up has not changed. I’m usually pretty good at spotting cause-and-effect, but this has me flummoxed.


Hmmmmmm . . . . OK, let’s think about it then. Oil change at the 15k checkup? Did they mistakenly use a really heavy weight? This is probably required to use 5W20, right?


Also . . . maybe the gas station pump has to be checked, maybe you’re not getting that extra quart or two of gas. Read the post on the premium gas and what’s left in the hose from the previous fill-up.


Happened before the service, and has not improved since.


Three different gas stations involved–no correlation with which place I filled up at.

Thanks, all! I think I’ll talk to the dealership.


Yes, but what did they do during your 15k service? It’s likely that they checked things which might not have any impact on the mileage.


I don’t know for sure off the top of my head–I’ll need to check the invoice tonight to see what exactly was done. I’m sure of oil change, tire rotation and alignment, but I need to see what else was done.


So the drop is NOT related to the service then . . . the drop started before the service was done and was unaffected by a tune up, air pressure check, alignment, oil change, etc? Gotta be driving habit/conditions/idling or miscalculation in the way the tank fills at the gas station . . . filled to “click”? Filled to overflowing? Filled to a few clicks over when the pump stopped?


I don’t know about where you live, but my Saturn has done the exact same thing, but I know why. Air Conditioning.


You said the word when you said front end alignment. Sometimes you get better mileage when the front end has straighter angles instead of what is specified. Especially the thrust angle.


I don’t know how many ways to say that NOTHING HAS CHANGED–not my driving habits, where and how I fill the tank, my route, the distance I drive each week, nothing. There is absolutely nothing I’m doing differently that could account for this.

Anyway, I thank you all for your suggestions. If it doesn’t “heal” itself soon, I’ll pursue it with the dealership. Thanks!


Is it possible that the gasoline in your area has been reformulated for seasonal changes? Or have they started adding ethanol to the gasoline? Either of these could explain the difference, especially the ethanol.


How about . . . extra weight in the car? An extra passenger? Weight in the trunk? Just trying to help you figure it out.