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Hello everyone: A firmware update was done about the time a recall was completed addressing the rusting brake distribution valve issue ! After the firmware was updated my fuel mileage dropped from 24mpg to 19mpg. I complained to my dealer who basically shrugged it off. I told the dealer I wanted to address the issue with Suburu's dealer support representative but I never hear back from anyone! Have others had a similar firmware result?
 

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2008 Subaru Outback PZEV,2010 Impreza 2.5i
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541 Posts
Hi!

When was the firmware update performed?

I assume that you have the model 2.5i with EJ253 engine. I also have the same car with the same engine and my firmware updates were performed years ago. I never observed any drop in fuel mileage at any time.
 

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(formerly) 03 H6 OBW , (presently) 06 WRX Sportwagon & 2021 Honda CR-V
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maybe a coincidence with a change in driving habits ?

how many tanks of fuel have been tested to yield the 19mpg number?

is the car new to you? is performance normal? does it start cold normally?
 

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2005 Legacy GT wagon 5MT Limited
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320 Posts
Any number of things could have happened at the same time. Vacuum leak, big chunk of garbage in the air filter, bad injector, blah blah. First step is use a scanner with live data to look at your fuel trims.
 

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2008 Outback 2.5
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999 Posts
Just a substantiated suspicion but the same thing happened to me with my 08 2.5i. I put off getting the reflash until Subaru forced the issue and mandated it so that I could not get my vehicle registration renewed unless the service was done. I was driving the exact same route to/from work everyday and the mileage went down from 25 mpg to 21 mpg.

Now that VW was caught and Subaru is "investigating" mileage cheating, I have the suspicion that the better mileage was how the car was sold to us, but the reflash of the computer was done to reduce emissions to where they should have been.

So much for a PZEV that "in some areas leaves the exhaust cleaner then the surrounding air"
 

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2008 OB Limited 2.5i, Portland OR USA
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8,508 Posts
We're talking about recall WVU31 - Reprogram ECM - which involves the following, in Subaru's words:

"This software update is intended to improve vehicle emissions when the vehicle is operated in cold weather and the engine is turned off and restarted within short periods of time such as in several minute intervals. This software change will not adversely affect fuel economy or performance."

So it likely isn't directly related to the mileage issue you are seeing, but it probably is related to a reset of of the learned parameters that the ECM had memorized. Give it some time; it should figure things out again.

BTW that SW update happened years ago, so your car was long overdue for this. Mine was done in July 2011, per my records.
 

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2000 Outback 2.5l 4EAT
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24 Posts
Does your car feel like it is breaking when you let off the gas? Or do you notice that you need more throttle to maintain your speed? Do you notice a hot/burning break smell from any corner of your car?
 

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'17 3.6R Touring Brillant Brown Pearl
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So, I hope your not depending on the dahsboard fuel economy display?

Another thought. Temps have been pretty cold all over the US lately. Winter blended fuel, and the ECM enriching the mixture can effectively drop fuel mileage 5-7 mpg.
 

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'17 3.6R Touring Brillant Brown Pearl
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Does your car feel like it is breaking when you let off the gas? Or do you notice that you need more throttle to maintain your speed? Do you notice a hot/burning break smell from any corner of your car?
How do you smell a break?

Im curious. It would really improve my diagnosis skills!
 

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2000 Outback 2.5l 4EAT
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24 Posts
After you've been driving a car a while you can get out and walk around to the corners and you'll smell a burning clutch type smell, only if you ride the breaks to get them to the point of break fade.

My break booster was rusted all up, and causing my breaks to have enough pressure so when you have the car up on a lift you could not manually turn the wheels. And talking to a couple friends back East where they have heavy salt on the roads they rust on the brake booster has been known to cause other brake issues. And when my brakes are seizing up like that it caused me to lose almost 6 points to the gallon to 18 ish mpg.

But this is just my experience, with a noticable drop in fuel mileage.
 

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2016 Outback 3.6R, 2007 Outback Sedan 2.5i
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9 Posts
Hello everyone: A firmware update was done about the time a recall was completed addressing the rusting brake distribution valve issue ! After the firmware was updated my fuel mileage dropped from 24mpg to 19mpg. I complained to my dealer who basically shrugged it off. I told the dealer I wanted to address the issue with Suburu's dealer support representative but I never hear back from anyone! Have others had a similar firmware result?
I have a 2007 2.5i Outback Sedan. The ECU was reflashed on the Recall notice years ago.
The MPG dropped off immediately after the reflash.
I changed wires, plugs air filter and transmission fluid but the MPG is never came back to 28 MPG.
I believe the reflash changed emissions to meet requirements.
Played games like VW did. :mad:
 

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I have a 2007 2.5i Outback Sedan. The ECU was reflashed on the Recall notice years ago.
The MPG dropped off immediately after the reflash.
I changed wires, plugs air filter and transmission fluid but the MPG is never came back to 28 MPG.
I believe the reflash changed emissions to meet requirements.
Played games like VW did. :mad:
You were getting 28 MPG? Wow. I stare at 20 MPG all the time.
 
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