Mysterious Drop in Gas Mileage

For the last two months there’s been a significant drop in my 2012 v’s gas mileage that I can’t explain. Since the weather warmed up at the end of June and for several thousand miles I’ve been averaging 46-48 mpg per tank in highway driving over the same route. I use eco mode and try to drive at speeds between 60-65 mph, modulating the peddle pressure to keep the HSI from exceeding two bars past the center mark.

At my recent dealer service (done in August at 13K miles) I had the dealer turn off the reverse beep. Other than that only routine inspection and servicing was done. Immediately after the dealer service my mileage started dropping and for the last five tankfuls it has been on a downward slope. My last tank over the same highway route averaged 42 mpg.

The obvious explanations for a drop in gas mileage don’t seem to apply. Ambient temperatures haven’t changed significantly. Tire pressures are checked often and kept at 2 psi above recommended values (37 front, 35 rear). There is no sign of a wheel alignment problem. The only thing I can think of is that something was inadvertently changed in the engine control module when the reverse beep was shut off. Is that possible? Or can other changes be made to the hybrid system that could account for the drop in mileage?

 

I check tire pressures every two weeks and always after a dealer service. 37/35 is what I've been using since new.

 

Oil level is fine. There was no oil change at this service.

 

Parking brake seems properly adjusted. When each rear wheel is raised it can be turned easily with one hand when the brake is released, spinning several revolutions although not free-wheeling. When stepped on firmly the brake engages fully at seven clicks.

So I'm back where I started, looking for reasons why my mileage has dropped. Again, maybe someone who understands how the ECU works could tell me if an accidental change in some ECU parameter, made while changing the reverse beep to a single beep could affect the hybrid tuning in some way.

Thanks to those who posted and tried to help.

 

No noticeable changes in the way it drives, in acceleration . But the instantaneous mpg readout tends to be lower than it used to be for a given driving condition -e.g when driving at 60-63 mph on a level stretch of road.

Also at low speed the ICE seems to run more than it used to but I'm not sure. It seems to want to charge the battery more often, keeping the charge level at 7 bars (used to be 6 bars). I could be wrong on this though...

 

Right. But what if the tech accidently changed some other setting in the ECU while attempting to turn off the reverse beep. Is there anything that could be altered in the ECU that might affect gas mileage?

 

If you read my opening post I am looking for a reason behind the recent falloff in mileage which started immediately after my last service in late August. I am very satisfied with gas mileage up to that point...and yes it did follow expected seasonal trends...up to that point.

Appreciate the comments though.

 

The service was on August 28, the day before that peak fillup. From that point on gas mileage just kept dropping for four straight fill ups. The latest fillup shows some recovery because I took special care to drive slower (< 60 mph) over this same route.

I agree that the 50.7 mpg peak is probably an outlier, but there is still an obvious downward trend even when measured from recent averages.

I am still hoping for an answer to my original question. Is there a setting in the motor ECU that, if altered, could impact mpg? Perhaps I should be asking this in the Technical Discussion forum?