Change in behavior on Instant MPG Meter

[colaboy]

First of all, hello everyone!

I am wondering if anyone has ever had this happen to them. I tried searching the forum and internet but could not find anything.

From last Saturday my instant mpg meter/gauge changed behavior. I think there is something wrong with it but the dealership says everything is fine. What is happening is, when I am barely going at a low speed, the battery kicks in and I get the max mpg, but the moment the gas engine kicks in, the level goes WAY DOWN, maybe in the 10-15mpg range. When I floor the gas pedal, its level is higher than when I barely press it. When I barely press it, it would go very low and slowly go up. When I take my foot off the gas pedal at any speed the mpg is supposed to shoot up to the max but sometimes it will get stuck on 75 and then max out. This is really weird. I've driven this car for over 6000 miles now and this is the first time it has acted like this. When you stop it's supposed to go to 0, but now there seems to be a little more lag than usual. I'm sure I'm still getting good mpg based on my driving habits, but something really is wrong with this meter...and since there is no error code it makes it that much harder to diagnose. Any help or recommendations would be much appreciated, the only thing the dealership told me to do was to keep an eye on it. Duh, I can't help but keep my eye on it.

p.s. if there is a thread about this, please let me know!

[efusco]

Sounds like normal behavior.
When you take your foot off the gas and it doesn't drop to zero it's b/c the ICE is still running and using fuel...it will do that unless you're in S4 of the hybrid stages of operation....and that won't happen until the ICE is warmed up and you come to a complete stop for about 5-7 seconds.

I suspect that the difference in behavior you're seeing has to do with the fact that it's hotter out and you're probably running the AC more, but nothing you describe sounds at all abnormal.

[Sufferin' Prius Envy]

With only six thousand miles under your belt, you should still be looking out the window at the road and not trying to do advanced diagnosis of what the Prius HSD is doing.

Everything you have said 'could' be normal . . . depending on the situation.

. . . could be normal if . . . the car isn't yet warmed up.
. . . could be normal if . . . the car is traveling at low speed.
. . . could be normal . . . often.

Don't worry about it.

IT sounds normal.

Just drive it.

[colaboy]

The car seems to drive normally so I'll just see how it goes then.

[JamesWyatt]

Try filling up with Shell gas next time. When I get a lower-energy tank of gas and/or a high level of ethanol, I will see this behavior. When I fill up at a Shell station, my mpg bar always as a rule shoots up to 100 mpg faster when I let off the gas. It also seems to stay there longer and not come down as fast when I lightly apply the gas pedal again. If I ever have to fill up at an Exxon or Chevron, the mpg bar struggles to get to 100 as fast. It seems to lag and take almost a second or two longer.

FWIW, once I filled up at a Kroger that had E85. Their normal E10 gas pumps didn't say, "may contain UP TO 10% ethanol" like other Krogers. Instead they said, "CONTAINS 10% ethanol". I got the worst mileage, acceleration power, and mpg bar response times ever in the 34K miles I've driven so far.

[colaboy]

I did fill up on Friday at a Chevron that I have not been to before. Maybe the next fill-up I can take it to my usual place. I am not inexperienced in terms of hybrids, my first one was the Honda Insight which I really liked until I needed a car with more than 2 seats.

I'll keep my eye on things, but still after driving 6000 miles, 7 months, in killer heat, rain, cold (insofar as CA gets cold), AC on, AC OFF, it's weird that the gauge would start doing this as of last Saturday.

[JamesWyatt]

It's not like the gauge is analog and will go out of adjustment. In a year and a half reading posts here, I have not yet heard of someone's mpg sensor giving false readings... maybe you could search for that, though.

I think your gauge is just reporting what the car is doing. Since no error codes show up, all fingers point to an external factor. I mentioned fuel because it is always your biggest variable to mileage and performance all_other_things_being_equal. (That is, same routes driven, same external temperature, same driver, same driving techniques, etc.)

Another possibility, you could have put in mid-grade or super by accident. The guage will really show a struggle for readings above 75 mpg with 92 octane gas.

[Patrick1928]

My prius has 125K on it and I am second owner having put on 30k of those miles. Just recently I unplugged the standard care battery in the back to do some work on the headlamps. Now the Instant MPG has this strange lag. It was very responsive until now. Now it jumps to a number and holds there for much longer then jumps either way up or way down depending on my driving.
The fuel is the same. The only thing that could have affected it is the diconnecting of the battery. I think this might be a calibration thing. There Could be a fuzzy logic circut here that has to relearn the curve. I am betting that this behavoir will smooth out as I keep driving, but that is just a guess. If It stays like this I will be very disapointed.
Regards,
Patrick

[Sufferin' Prius Envy]

Originally Posted by Patrick1928

Now the Instant MPG has this strange lag. It was very responsive until now. Now it jumps to a number and holds there for much longer then jumps either way up or way down depending on my driving.

Welcome to PriusChat. A Prius driving Northern Californian named Patrick. You must be one cool dude! And if you are driving a Salsa Red, it's confirmed!

After having driven your Prius for 30,000 miles, I'm hoping you noticed that the instantaneous MPGs aren't really instantaneous, AND instantaneous MPGs will jump wildly up and down for the first few miles after a gas fill-up.

If this somehow erased some fuzzy logic, I'm fuzzy on that one.

[jps000]

I had a Honda Insight for 7 years before that. Can't beat that comeback.