Sudden drop in MPG

Normally for conventional cars, the 12V battery (which is the Prius aux battery) voltage should read about 13.8 volts when new and about 13 volts when in good condition and about 12.5 volts when it needs to be replaced. If the Prius Aux battery works like a conventional car 12 vdc battery - then your Prius aux battery reading of 12.39v signals the need to replace it with a new battery. I've read in this forum that a bad/dying Prius Aux battery in the 1st and 2nd gen Prius will cause random and strange problems...

 

Very untrue!
Please edit the post and remove the glaring mistakes.

 

Well, you didn't explain how you evaluated the 12V battery, but the voltage you provided is well below the fully charged battery.

Second, you didn't answer what gasoline you use and if you ever did injector cleaning.

 

Ah -- If only things were that simple....

A mobile radio transmitter drawing from an automotive 12VDC line will need up to 13.8 VDC to output at its highest power level.

I've read multiple times where the gen2 Prius onboard computer and sensors will exhibit erratic readings/behavior when the aux battery needs to be replaced. While a battery's state of charge (and ability to hold a power) is estimated by measureing the battery's voltage level - the amount of power/current level that a battery can sustain/provide will vary widely from the voltage level. However, usually as the voltage drops - so does the battery's ability to sustain a current level high enough to run its expected load. A battery may look find alone when tested with a voltimeter but still not be able to handle a circuit's load requirements.

 

Which part of Alabama? I'm in Huntville.

Full, defrost mode hits mileage and is easy to forget. Just to the left is 'heat' based, defrost and it is much more efficient. I use the right-most defrost only to get rid of the initial fog and then back to 'head' mode.

Bob Wilson

 

I have a 2011 Prius 4. My mpg has dropped significantly. On trips that I would get 52-54mpg (Prius) I know get 36 - 42. I can really tell the difference in the transmission when I get better or poorer mpg. Also, I can be going down a grade and the mpg bar does not reach 50 on the bar with a full battery and sometimes I can be going up a grade and get 50 on the bar. I am really confused. Two other things: my Prius initially had a short sound (like a clutch on a drill), then once I started the Prius and it sounded like all sorts of things were flying around under the hood (I actually thought the transmission was coming apart). I started it again and it ran okay. They found nothing at my next oil change. Then one day I put it into gear and the cluth(?) sounded clunky, then okay. Now that drill clutch sound is back to almost every time I put the gear into D and just recently started to occasionally make the drill cluch noise just when I start the Prius. By the way. I have had significant variations in mpg since I got my Prius. A couple of months ago, I was getting 53 to 57 mpg without effort. The mpg now, varies from 36 mpg to 55 mpg. not much over 44 for the past several weeks. Am I concerned. Yup! This Prius will go in for a check up. :>{