MPG drops then resumes

I was on vacation for all of December and logged zero miles. When I returned, my car started right up. It sounded a little rickety and the check engine light came on. After two days of driving, the light went off. However, the MPGs dropped from my lifetime average of 42 to barely 30... a 25% drop. I spent the last month scanning the forums and reading conversation threads on topics that could be related to me without starting ANOTHER redundant topic.

While many traditional solutions are frequently presented... there was a curious outcome amongst the MPG problems... the problem magically went away.

This just happened to me this week. I’m back to 40-45 with casual, non NASCAR, driving. The most immediate thing I did before this realization is that I cycled the driving modes from eco, to off, and turned eco back on. No clue if it’s the solution

I was prepared to clean my EGR system, go to 0-16 oil, question my tire change choice (non LRR), and change my aging but perfectly fine 12V. I did however buy a bluetooth OBD to check traction battery life. It’s about time to anyways.

I just wanted to contribute my observation after spending hours reading all of the contributions the helpful faithful have provided on priuschat.

2010 Prius III
185k miles
Second owner @ 96k miles
Original traction battery
Oil change every 10k with Amazon 0-20
Trans fluid changed at 150k miles.

 

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One month.

During the month of January, I was fueling up every three gallons, with worsening to static results. I ruled out Lupus too.

 

I am leaning toward a vague answer much like this. I believe there is something happening behind the scenes regarding the computer compensating for a variety of sensor inputs or lack of sensor inputs. I believe this is the answer for many of these "sudden" drops in MPG. The weather here dropped precipitously which correlated with the drop in my MPG. December through January maintained temperatures below 0*C.

 

PS. Trying to keep my footprint on the forum low so ill freeload off my thread. If anyone has any insight into buying a replacement 3rd GEN traction/HV battery in continental Europe, let me know. Double points for install services. I have not found any information in the forums on resourcing a battery in any of the recent-years threads.

 

I brought it from the states but that’s an awesome fact

 

That’s a great point too. Only when the MPG was back did I bother to hook up the multimeter: 12.6 cold / 14.7 with engine on. Many love swapping out their batteries preemptively but I’m a drive it until it dies kinda guy on the 12v.

 

Yeah my battery is approaching the same with nearly 7 years.

 

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I wanted to have my car and the shipping cost was reasonable.