Toyotas failure

I've disconnected my 12V battery twice since I have owned the car and both times I experienced the opposite from your description; the mpg went down for about two tankfuls before it returned to the "normal" mpg that I was getting before disconnecting it.

In the service manual, it does describe that you have to "reinitialize" the vehicle after disconnecting the 12V battery - you must perform the initialization of the auto up function for the drivers power window.

 

Check the first paragraph of this collection of mileage hints (for rallying) by Hobbit:

http://techno-fandom.org/~hobbit/cars/prius-rally-hints.txt

 

For as long as I can remember Toyota vehicles always can be "rebooted" to turn off the check engine lights, and other warning lights. Once it turns on, it would recheck all the electronics and engine. If the problem still persist, then the warning lights will come back on. My oxygen sensor broke on my Tacoma. I replaced it, disconnected the battery and reconnected it. It turned off the ck eng lt and erased all the codes. This was verified with OBD scantool

 

pretty much any car's ECU can be reset if you disconnect the battery long enough. But why bother, if you had an OBD scan tool you could've just cleared the code yourself. easy doin =)

 

Not all OBD-II scantool can clear codes. The one I have access to only reads the fault codes. That's why I knew the oxygen sensor was bad.

 

Perhaps some of the reduced mpg cases involve something the ECUs have 'learned' that is actually hurting fuel economy. This would account for andy's mpg recovery.

Barring such unexplained mpg reduction, rebooting cannot help.

In all cases, rebooting will require the ECUs to relearn things, some of which normally improve mpg, explaining hobbit and dogfriend's experience.

When my PC locks up or slows to a crawl, I reboot and voila! When not having trouble, a reboot just takes my time.

 

I had my 12V battery disconnected for a couple of hours earlier this year while working on the car.

I was pleasantly surprised to find that the settings for the seat belt beepers and the reverse beeper were retained. I did have to reset the audio system buttons and some of the settings in the Nav system, the destinations and addresses were retained however. The trip mileage records and fuel consumption history were gone and the clock needed to be reset. I had checked the codes before and didn't have any so I don't know for sure if they would have been reset or not but I think they would have been.

After restarting I noticed the idle speed was a bit high and the car ran a little weird for the first few miles but everything was back to normal after 20 miles or so. I think virtually all cars made within the last 10 or 15 years have "tuned themselves" as you drive and will reset the engine management system when the battery is disconnected for 15 minutes or so.

 

The computer tuneup theory is silly. Rebooting your Prius can help mileage, but only if the electronics are locked in a disallowed state. This has happened a few times, mostly with the JBL power amplifier, where the amp fails to turn off with the car. Extra power consumption equals lower mileage, plus, of course, the risk of a dead battery.

As for generally improving your Prius mileage as if you were doing a computer tuneup, it doesn't happen. There is a very real chance that you will see improved mileage on the display, but this comes from dumping lower mileage from the running average. It's not a true improvement.

Most modern cars are self tuning. Over time the engine ECU adjusts to the characteristics of the engine and fuel. Some also adjust to driver habits. Resetting the ECU causes the tuning parameters to be lost, resulting in poorer performance while the ECU relearns.

Tom

 

Just rebooted today and it does seem to help a lot!
So far, it's gained upto 46mpg from 42mpg and I believe it's still climbing rapidly after 15 miles from rebooting...

Strange that my 1st Prius G3 did not require this reboot, I was consistently returnning 45mpg real world regardless of my driving style.

Maybe this later Prius built YE is not the identical setup as earlier versions. I've been meaning to post this effect...

 

I rebooted mine 5 times in a row, inflated the tires to 100 psi and turned off the air conditioner. I had a half tank of gas and set off on a 200 mile trip. When I returned home I had a full tank. :rockon::cheer2:

 

maybe toy will design the eleven so it will reboot everytime you turn it off and on like your computer without forgetting your current average so we won't have to keep going thru all this.