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Discussion Starter #1
I took my car in to the dealer on Thursday, 11-19-14 to have the PCM flashed to solve the flickering headlight issue described in TSB 01-019-13. (I also had the tires rotated.) Now my dash MPG gauge is showing that I am getting 5-6 less MPG than I was before. I was averaging around 37.0 mpg combined, and now it is showing around 31 - 32 MPG combined. Has anybody else had this happen, and was Mazda able to provide a fix without the flickering headlights issue showing up again?
 

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Your computer probably just needs to relearn everything to get the most efficiency out of the car. Reset the MPG gauge after this tank of gas and see if it returns to normal. If it is still significantly lower, then I'd talk to the dealer. It's also possible your tire pressure is a bit low. They typically check and reset tire pressures when they rotate tires, but if your tires are warm when you come in and they read higher than the (IIRC) 36psi, an inept tech may lower it thinking they were overfilled. Check your tire pressures when they are cold in the morning and fill as necessary.
 

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Discussion Starter #3
Thanks for the reply Outtaluck. There was such a drastic difference in the MPG that I disconnected the battery, and then re-attached it. It seems to be hanging around 32.7 MPG right now, where it used to read 37.4 MPG.
I understand if it read a little bit lower because the TSB was also for an undercharging problem, so if they are putting more load on the alternator, then that could lower the MPG, but I thought 5 MPG +/- was a little too much.
I thought about the tires, but haven't had a chance to check them yet. Gonna take a long trip for Turkey Day, so thought I would bump up the air pressure before then to get a little bit better MPG.
Thanks for your time.
 

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Discussion Starter #4
On the plus side, they did fix the flickering headlight issue, so now my car no longer gets mistaken for an emergency vehicle! Ha!
 

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I've had a similar drop in mpg's end of last year. Dealer "reflashed pcm with the latest calibrations" while it was in to be checked out (Steering angle sensor intermittently not working).

I just figured it was due to colder weather gong into November combined with Speed3 front/ 5 rear brake upgrade with different tires/rims.
 

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I've had a similar drop in mpg's end of last year. Dealer "reflashed pcm with the latest calibrations" while it was in to be checked out (Steering angle sensor intermittently not working).

I just figured it was due to colder weather gong into November combined with Speed3 front/ 5 rear brake upgrade with different tires/rims.
Did your MPG ever go back up in the spring? I just finally had my car reflashed and my mileage went down 5 plus mpg. I just figured since it got cold here that was the cause (I normally drop 5-10 in the winter with this car) But its interesting that others are seeing the same thing.
 

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Did your MPG ever go back up in the spring? I just finally had my car reflashed and my mileage went down 5 plus mpg. I just figured since it got cold here that was the cause (I normally drop 5-10 in the winter with this car) But its interesting that others are seeing the same thing.
Nope, struggling to hit 40mpg's highway these days too.
 

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Discussion Starter #8
I checked the air pressure in my tires this morning when they were cold, and they all read right around 40 PSI, which is about where I usually keep them inflated. It is interesting that other people are getting reduced MPG after getting their PCM flashed by the dealer. Assuming they all followed the same procedure, then it has to be a problem with Mazda. It has been cold enough so far around here, and I visit gas stations that do quite a bit of business, so all the gas was winter blend both before and after the PCM flash.
 

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Discussion Starter #9
Just an update. I took a Thanksgiving trip that was about 2-1/2 hours each way of mostly highway driving. The tires were inflated to 40 PSI, and there were 3 people riding in my Mazda3, along with various other items like luggage, food, etc.
I averaged about 34.5 mpg on the way down. The mpg gauge on the car finally clicked over to 35 mpg about 15 miles from our destination.
On the way back, I got 36.5 mpg. Some of the increase was a 15 - 20 mph tailwind pushing us.
It's not the 37 to 38 mpg average I was getting before the PCM flash, but still better than I thought I would get immediately after getting the PCM flashed. (Maybe the car does indeed need to re-learn everything!) Right now I am getting right around 36 mpg in combined city/highway driving.
 

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yeah you are kicking my ass in mpg lol i average 32. i took a trip recently and averaged 32 all clear flat highway miles! terrible for this car.
 

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@Displayhawk

Are you verifying your mileage at the gas pump? It may be that the PCM flash causes the trip computer to underestimate MPG.

Also, any noticeable difference in acceleration or engine braking? I can feel it with the AC compressor cycling. Alt load should be nearly invisible to the driver. If it really were a load from the alt causing that much loss in MPG I would think that the alt would've burned up by now.
 

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i had my pcm software updated about a month and a half ago at a mazda dealer. i have noticed my fuel mileage going down about 100km a tank less than b4 . but the car feels like it has more power so i would assume thats why. i like the power but im a bit more cautious when driving in the boonies where the gas stations are few and far between.
 

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Discussion Starter #14
My mileage is staying at 35.5 MPG for combined Highway and City driving. Been stuck at that number for about 2 months now.
 
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