Sudden mpg drop after service check

please check them yourself

First off, you've posted in the the wrong area. You have a Gen II. I've flagged it for the mods to move it to the right area. Anyhow, welcome. :welcome:

You need to go and check the oil and tire pressure yourself. Having it "handled by the dealer" doesn't tell us anything. I've and others on PC have had personal experience w/dealers overfilling oil while doing oil changes. I've had dealers more than once muck w/my air pressure when I told them not to. In the most recent case, when they lowered my pressures to 35 F/33 R, I told them to bump them back up to 40 F/38 R. Service advisor replied, ok, we'll get someone to do it. I get home. Guess what? There were still at 35/33.

Regarding checking the 12 volt battery, there's a link to the method in http://priuschat.com/forums/gen-ii-...-answer-these-questions-esp-if-youre-new.html.

As for manual calculations not necessarily matching that of the MFD and the going back and forth w/the readings. That's totally normally. I've seen that since day 1. You need to average out both, over time.

Don't use B mode at all.

From 10 Day Weather Forecast for Austin, TX - weather.com, your temps have dropped but I doubt they'd be enough to cause a 20% drop.

 

Welcome to PC. Sounds like there was a screw up at the dealership. When one can show litterly years of MPG tracking and that suddenly changes and the change happens in the middle of a tank full but coinsides with a trip to the dealer, well, is it JUST coincidental? I think not!!!
I don't know if you'll ever know the truth, but an educated guess from the evidence would suggest something fishy happened at the dealership while in for service.

 

It sounds to me like they cleared the computer.... It will take about 3-6 weeks for the computer to re-learn your driving habits and adjust accordingly... If they tested your 12V battery, this could have done it. Some dealers disconnect it to do the load test to protect the electronic systems.
Each time they cleared it on me, I got crappy MPGs for a few weeks until the system re-learned the hyper-mile strategy.

 

whoa whoa whoa, the government has recently been putting additives in gas that lowers mileage for prius/hybrids??? Is this true?

 

I'd like to know more about this. I've read the theory floated several times but haven't seen much detail. Is it really so smart as to "learn" how I drive or is it more about the computers adjusting to how the car is performing?

- D

 

Don,

I'm not sure it's really learning, more like data collection.
Anyway, smarter folks than me talk about it here:

http://priuschat.com/forums/gen-ii-...w-what-does-prius-cpu-s-learn.html#post593362

 

Check your oil, 2/3rd's up the dipstick is preferred, not at the top, cycle your emergency brake on and off a few times, they may have adjusted the shoes tighter, manually. Change out your 12 volt battery for an Optima yellow top and it's fit kit. Pump your tires up to 42 front 40 rear, check your engine and cabin air filters, clean the cabin filter in the sink with soap and water, replace the engine one or if it's a K&N clean and oil it.
Assume they unhooked your battery and wait two tankfuls before the mileage is a concern.

 

Yes, Every fall, and then every spring they put it back.
The Oil Drum | Refining 101: Winter Gasoline

 

I, too, have experienced almost identical sudden fuel mileage drop symptoms as you describe. It was following my 30K service in July, 2010 (2008 model) and I also had the recall gas petal replacement done at that time. Immediately following the service, my mileage dropped from 45-47mpg to 38mpg tops. My original tires were worn so we replaced them, and still no improvement. I've had the same issues with fuel fill up as you describe - the low fuel indicator light comes on and the fuel input clicks off at 8.9-9.0 gallons when previously it was higher. I don't have any problem with the outside air temp reading, but the computer calculating the mileage seems to fluctuate erratically though it matches my manual calculations of 38mpg. No luck with the dealer, same as responses you describe.

Have you had any further luck resolving this matter?

 

What else changed around that time? 40 mile commute became 2 miles? 300 pound guy joined your car pool? ran over a tree trunk? started using "B" instead of "D"? It's amazing sometimes what people can forget, or forget to mention.

Otherwise, check the tire pressures (42/40 PSI front/rear will help a lot), make sure that the oil isn't overfilled, and that the parking brake isn't hung up. Get a diagnosis from another dealer.

 

Cold weather and new tires can account for all of this.

What type of tires did you get? (exact size model brand please)

 

Not enough info. Please answer http://priuschat.com/forums/gen-ii-...-answer-these-questions-esp-if-youre-new.html.

Even if you replaced your tires w/identical make and model, expect to see some drop, at first. See Tire Tech Information - Tire Rolling Resistance Part 3: Changes to Expect When Switching from Worn-Out to New Tires.

 

Yep, I went to SAMS and had the rear tires replaced on my Honda hybrid and my milegae went up. So stupid me thought, " do the fronts and get even better MPG". Stuck on 38 MPG/ARGH!. Tires, thick oil, tire pressure, and what else did they do to your car. Somtimes the traction battery not properly charging and kicking in when it should will drop your MPG. Love my Prius BTW. I always get better MPG than with my Honda.

Odd, but I have noticed in the last 30 days that my tank won't fill up all the way unless I slow fill it. I wonder if they adjusted the pump pressure shutoffs.

 

I wonder how many of these threads are based on owners having their lifetime mpg trip meters reset. Unless you reset the meter yourself on a regular basis how do you know your mpg has really dropped? My 2005 resets everytime I filling the tank but the 2006+ models do not automatically reset. Is that correct?

 

Sounds right, I have to reset my 2007 manually.

 

Why would anyone allow a "Stealership" to handle their oil and tire pressure? Their numbers are not for your benefit.

 

My 2008 Prius has done the same thing. Mileage always around 50 mpg. 41,000 miles. Since 40,000 mile oil change and tire rotation mileage has dropped to 38. No change in driver/driving. New tires were bought at 35,000 and mileage the same as before with those.

 

Check the easy likely stuff first: the oil level and tire pressures.