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"Reset the computer for better mileage?": I'm a believer (long post)

7K views 4 replies 4 participants last post by  TrailDust 
#1 ·
I am including more details than normal to highlight the path of discovery and diagnosis that others may be on.
VEHICLE: 2017 Highlander Hybrid Limited Platinum

I had been tracking fuel usage and mileage since very beginning (February 2017), including type of fuel used (ethanol vs. not), fuel source, and relative weather conditions (since temps here vary by more than 100 degrees F during the course of a year, with the extremes having a huge adverse impact on fuel economy).

In late 2018, after driving it for about 18 months, it seemed like I wasn't getting as good of fuel economy as initially -- mainly based on the vehicle's dash reading itself. I did some experimenting with 1) avoiding ethanol-blended gas, 2) using ECO mode vs. not, and 3) trying extra hard to improve my fuel economy. Nothing made a difference. By Thanksgiving I was at about 32000 miles, and decided to replace the factory tires with something better suited to a potentially severe winter. I sacrificed the low rolling resistance for better gription = Goodyear Assurance Weatherready. Put the same on our 2013 Ford Fusion Hybrid. No additional / noticeable drop with the more aggressive tires, and my wife said the Fusion did not drop with them either. (she averages in the low- to mid-40's, and tracks very closely)

Earlier this year I finally entered all of my fuel usage data in to a spreadsheet so I could dissect in more detail. I computed the MPG for each fill, plus a rolling 4-tank average to better account for variances. The results were telling: From a consistent 30mpg (mild temps) to 27mpg under similar conditions (25mpg if heavy A/C use, or 22mpg at its coldest). At best it was not far off the EPA ratings (29 city, 27 highway) but definitely below previous performance. Have not approached 30mpg since last August.

Before heading to the mechanic, I did a lot of internet research. I ran a couple of bottles of Chevron Techron, and bumped up the air pressure in my tires a bit. Neither made a difference.
THEN I checked more details about resetting the computer (ECU), as I had read in a few places, in case it was using some inappropriately-remembered settings. Not knowing exactly which fuse did what for this model, I pulled multiple -- from those labeled EDU to EFI to ETCS to ECU-IG. Upon startup I did not notice that any settings were missing or reset, and it ran fine, so I wasn't sure it had reset anything. A half-hour test drive was showing similar MPG readings.

I saved disconnecting the 12V battery for last. I left the NEG terminal off for an hour, then reconnected. (realized later that I didn't try to more fully drain any electrons in the system) Upon startup the engine was still warm and the big batteries well-charged, so the gas engine did not engage right away. After several seconds it finally did, ran perhaps a bit rough for a bit, then smoothed out and shutdown soon after.
I headed out for another test drive, taking it easy. Outside temp around 80, window down, A/C off. I reset the vehicle's gauge upon reaching a flat area. Going 45mph I was getting 33mpg, whereas for the last several months it would probably have been 27mpg. Did some minor hills, stop-and-go, city driving from 35-45mph. End result still around 33mpg.
The next day I headed out for a longer drive. City driving with hills and consistent 40-45mph, followed by flat highway going 50-60mph. I was averaging 35mpg and loving it -- fully convinced that it was better than ever. It did drop after more hills and more frequent stops, then return home totaling 80 miles. Final average was 31.5mpg for that trip. Undoubtedly better than the previous year, but not even a full tank therefore too early to declare victory.

Finally filled up this morning after 9 days of a typical city/highway driving. MPG was 29.5, and that includes about 50 miles (out of 423 since last fill) that took place before the computer reset. The previous 1500 miles had averaged 26.1 mpg. Easy 10-13% improvement.
I will continue to track and monitor. 1000 mile trip next week will provide another good test.
 
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#3 ·
Not overt BS, but it didn't last either -- at least not at the 29.5 level. Running average has been more like 27-27.5 over the past 2 months instead of 26 before, but I'm still trying to see if there are other variables involved.
For example, on that 1000-mile trip soon after the reset, I got 27.9 using Costco mid-grade 10% ethanol while going from 1200 to 3700 (above sea level) over the course of 390 miles.
Next I got 30.0 after filling with premium (probably no ethanol) at a no-name station that was going out of business, in the middle of nowhere and I was getting close to empty, and going from 3700 feet up to 5400 and back down to 3200, over the course of 423 miles, and using the A/C.
But then with the very next fill, using mid-grade 10% ethanol, and a gradual drop from 3200 down to 1200 feet (which should have been good for mileage), little A/C use, I only got 25.9.
So then I experimented with using premium for a couple of fills, just in case. No big difference.
I'll also try the reset again, just in case, to see if I get another bump. The 29.5 and 30.0 readings may have been outliers.
 
#4 ·
2016 Avalon Hybrid Limited, bought it 9 weeks ago, 58K miles, so still learning how to squeeze the most out of the mileage....just because... When I picked the car up, the average mpg was 33 something, so I reset it. After about 800 miles I reset it again since I learned a bit more. Then I reset it a 3rd time after mixing in a bit more eco button. Now colder weather has set in, so the average is falling a bit, from 46mpg. (I did hit 46.3 for a while before a few hills took it away) For me I don't like to see going up a hill drop my average back 1 mpg or more so fast. Everyone "falls off the wagon" now and then, getting somewhere on time or just accelerating into traffic. So it is nice to be "absolved" of a few "sins" here and there by resetting the average. Just the same, I look into the rear view mirror and say to someone following me "sorry pal, I'm not sinking my mpg average for you".

Try not using the eco button for 1 day, as maybe the battery needs a different kind of "exercise". I hadn't been using the eco button much, then it seemed miraculous how much the computer was telling me how much I was getting....yet the average was not going up enough (as far as I thought it should) to make it believable. I try to move around parking lots not pushing the gas too much so the ICE doesn't come on, will try to get it below 45mph so the ICE will cut off going down hill (in the proper places where speed limits are 45mph or less). I travel in normal, sometimes eco, never in sport....EV is a total waste of a good button...it's gonna do what it wants to do...like herding cats! I apply the brakes slightly, going downhill to recharge more, but not enough to make the brake lights come on. It is good to reset....but just as effective as cheating @ solitaire....in the end...you know. Just brag about what it did last week...and not what it did today. (y)
I'm going to try the EV button a few more times, like when I know the battery is up near the top, and see what happens. I have the power distribution screen up at all times, when the GPS is not being used.
 
#5 ·
I realize the ECU reset thing is as controversial a subject as dino oil versus synthetic, K&N versus paper filters, or top tier gas. For myself I believe it is true and makes total sense, although don't expect some massive change in mileage. My primary experience with this was when I brought my Highlander home from the dealership. My HL was special ordered, and was not delivered on a truck but rather hand-driven from the ship at port. That put 60+ miles on my HL, and we all know that every single gorilla who works at dealerships and auto shops smash the accelerator to the floor when behind the wheel. Anyway, my first mileage was atrocious and posted that to TN way back, and the suggestion was made to reset the ECU. I did that and the mileage jumped almost twenty percent.

Relearning your personal shift points and driving style makes sense that an ECU reset can improve mileage.
 
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