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Discussion Starter #1
2019 sedan premium

Based on the instrument panel, my "avg mpg" started out around 31 mpg. Over 1500 miles it has dropped to 25.4. I get about 370 miles per fill up, 11.4 gallons - that's over 32 mpg (a lot of highway). So I don't believe the 25.4.

I made a 30 mile trip today on the highway. The car said my "avg mpg" was 25.5 when I started the trip. Then the fuel efficiency monitor (center display) said I averaged 39 mpg on the current trip. When finished, my "avg mpg" was 25.4. The software is messed up.

Anyone else see this?
 

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Mileage monitors are often inaccurate. The most accurate method is what you did, take note of how many miles you drove and divide that by the number of gallons you have to refill.
 

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I am also having this issue. My trip mpg is high from the "fuel efficiency monitor", but the avg in the instrument cluster keeps dropping lower and lower.
 

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Discussion Starter #4
xmcacx - I hope you will call Mazda and tell them. I have done this (no response yet) but I think it helps if more than one person has the problem.
 

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I am also having this issue. My trip mpg is high from the "fuel efficiency monitor", but the avg in the instrument cluster keeps dropping lower and lower.
Mine has done the same twice now. I drive about 100 miles round trip to work and back each day and average 39 to 40 MPG and even though the fuel efficiency reads low 40s my average will drop constantly to 25 - 30 MPG. After I reset it it will stay true for a few weeks until it happens again. I mentioned it to my dealer service tech and asked if it was a software bug but there were no updates out yet and I was the first to mention it to them.
 

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my 2019 mpg display says 11.5 mpg. that is worse then my 2003 7.3 liter diesel F-250 4X4. most of my driving is highway with about 9,500 miles so far.
 

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This is a know issue, Mazda issued a TSB few weeks ago here in europe for this issue Ref. No. R045/19

Basically displayed averge fuel economy will get worse after 2000 Km or 1200 miles without reset, this is in display only not actual increase in fuel consumption, the BCM needs to be updated with new software, affected VIN in europe are JMZBP******1000001 - 123730
 

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This is a know issue, Mazda issued a TSB few weeks ago here in europe for this issue Ref. No. R045/19

Basically displayed averge fuel economy will get worse after 2000 Km or 1200 miles without reset, this is in display only not actual increase in fuel consumption, the BCM needs to be updated with new software, affected VIN in europe are JMZBP******1000001 - 123730
Thanks for the info. I will check with my dealer.
 

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Has anyone with a North America Mazda 3 had this problem fixed? Our Mazda 3 has this problem and the dealer could not find a problem. Is there a related TSB for North American models? Thanks.
 

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Discussion Starter #10
Not fixed, but I set the menu to reset the gas mileage whenever Trip A is reset, and I reset at each gas refill. It is accurate for one tank.
 

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This is a know issue, Mazda issued a TSB few weeks ago here in europe for this issue Ref. No. R045/19

Basically displayed averge fuel economy will get worse after 2000 Km or 1200 miles without reset, this is in display only not actual increase in fuel consumption, the BCM needs to be updated with new software, affected VIN in europe are JMZBP******1000001 - 123730
Man, do you have access to this TSB pdf? 🙌
Can't find it anywhere on the web.
 
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