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Discussion Starter · #1 ·
I saw people complaining about the Avg MPG gauge circa 2011 time frame but haven't seen others of recent. I assume the problem had been fixed in our generation cars, but obviously not.

Anyway, my Avg (not Instant) MPG readout
1) may or may not start out from the same reading as when I last turned the car off
2) May stay constant or frequently change when traveling on high way or suburban roads. At highway speed traveling for 20 miles, the readout stayed a constant 33.2 mph. Never saw that before. Then again, on suburban streets, travels a few blocks from one light to another, the tenths place digit was increasing and decreasing about once every 5 seconds or so.

Just FYI, always reset the mpg guage on fill ups.

In the older post one person suggested unplugging/replugging he ECU unit (I guess to reload the firmware). Don't know how to do that. Any other suggestions?
 

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2013 Ebony SXL Turbo: Original Everything @ about 189K with Drag wheels.
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Or average can be calculated the old school way, at the pump doing some simple math, haha.
 

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2012 Black SX Prem. & Tech.
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The AVG (not instant) MPG uses your past and current MPG, so it will also fluctuate depending how you drove previously and how you are driving now. It doesn't change as fast as instant, but it will change in a similar manner averaged over longer periods of time.

There is an option to have the car automatically reset the AVG MPG on fill up for you, so you should consider turning that on. The car is intelligent enough to know whether you are just adding a little bit of gas (no reset) or a fill up (reset).

You can always manually reset the AVG MPG, even if you turn on automatic reset on fill up. You can play with this by coasting down a hill and resetting the AVG MPG. After a bit the AVG will show like 99 MPG and then stay that way for a while (depending on how long the hill is).

But bottom line, the impression from your post is that the AVG MPG function is working properly in your car. Was there something you saw that you thought was not right?

1) the AVG MPG will constantly update when you are running the car, because idling uses fuel and results in zero miles. I'm guessing you turned off the car right before an update, and so when you turned on the car, it updated the AVG MPG.
2) constant vs frequent change - this depends on how recently you reset the MPG, and also how "differently" you are using the gas pedal. Constant cruising and the AVG MPG seems to not change much, but if you accelerate and decelerate you'll see more frequent updating. Or if you just change the gas pedal position without really changing your speed, like if you have an uneven or hesitant foot. perhaps try cruise control on a flat surface? (Hills will cause the cruise control to vary the throttle and change the AVG MPG)

Another option would be to disconnect the car battery and let the car sit for a while like that to reset. But I wonder if that will just be the same as manually resetting the AVG MPG using the dashboard interface. I don't think either reset will solve a problem with the sensors or the computer. However it sounds like there is no problem?
 

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Discussion Starter · #4 ·
The AVG (not instant) MPG uses your past and current MPG, so it will also fluctuate depending how you drove previously and how you are driving now. It doesn't change as fast as instant, but it will change in a similar manner averaged over longer periods of time.

There is an option to have the car automatically reset the AVG MPG on fill up for you, so you should consider turning that on. The car is intelligent enough to know whether you are just adding a little bit of gas (no reset) or a fill up (reset).

You can always manually reset the AVG MPG, even if you turn on automatic reset on fill up. You can play with this by coasting down a hill and resetting the AVG MPG. After a bit the AVG will show like 99 MPG and then stay that way for a while (depending on how long the hill is).

But bottom line, the impression from your post is that the AVG MPG function is working properly in your car. Was there something you saw that you thought was not right?

1) the AVG MPG will constantly update when you are running the car, because idling uses fuel and results in zero miles. I'm guessing you turned off the car right before an update, and so when you turned on the car, it updated the AVG MPG.
2) constant vs frequent change - this depends on how recently you reset the MPG, and also how "differently" you are using the gas pedal. Constant cruising and the AVG MPG seems to not change much, but if you accelerate and decelerate you'll see more frequent updating. Or if you just change the gas pedal position without really changing your speed, like if you have an uneven or hesitant foot. perhaps try cruise control on a flat surface? (Hills will cause the cruise control to vary the throttle and change the AVG MPG)

Another option would be to disconnect the car battery and let the car sit for a while like that to reset. But I wonder if that will just be the same as manually resetting the AVG MPG using the dashboard interface. I don't think either reset will solve a problem with the sensors or the computer. However it sounds like there is no problem?
Thank you King,
I am the original owner and know what's normal and what isn't. turning the car off when the readout reads 38.7 and the next meaning upon start up, the avg mpg read 33.4 is not normal. I have to take the car to the dealer to service a safety recall notice and will see what they have to say and post back to you. look for it in a week or so. thanks again mr Fatty and stay safe
 
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