Attention Prius Owners, I believe I have discovered a previously unknown Mechanism of Low MPG.

Mendel Leisk · Jul 15, 2024

Trivia: to convert km/100km to mpg (US gallons), or vice versa, divide either into 235.2. I forget how I arrived at that, but it's just a distillation of the conversion process.

Troy1994 · Jul 17, 2024

Mendel Leisk said: ↑

Trivia: to convert km/100km to mpg (US gallons), or vice versa, divide either into 235.2. I forget how I arrived at that, but it's just a distillation of the conversion process.
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That’s handy, thanks!

Frankusa94 · Aug 24, 2024 at 8:22 AM

wr69 said: ↑

I've had the 12V battery unplugged on several occasions on my 2010/2013. At times, it was unplugged for a week - due to my negligence in not having the correct assortment of parts. I never really noticed the MPG's drop after such events. Anytime you futz with a circuit, which has computers in it, you risk static discharge potentially frying the motherboard of the computer. It would not surprise me if its possible to fry the a Prius ECU with a static shock during such exercise. From experience, I had a bad Main ECU and the car ran fine and didn't throw any codes, but failed to beep when locked/unlocked. Very annoying problem, which I eventually had to solve by process of elimination and trial and error - not much info on the Prius computers floating around on the Internet. The other thing I could envision is maybe 12v battery might be going bad and disconnecting it triggers final failure; and MPG doesn't recover due to bad 12V, but I have no logic to back that up ATM.
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Your post made me realize my 07 Prius no longer chirps when doors are locked…and I am also experiencing 40mpg in city and 50+mpg on drives above 40 mph. I did disconnect my 12v a few months… and ICE immediately kicks on with the very little pedal press. Must be an easy way to restore max ev … has anyone spoke to Toyota about this?

Frankusa94 · Aug 24, 2024 at 8:41 AM

TheLastMojojomo said: ↑

I know the post is alot to take in and very schizoy... you do not want to disconnect the 12v Battery. Disconnecting the 12v Battery is what causes the WEAK EV State... you want to avoid disconnecting the 12v at all costs.

The commuting however may activate the MAX EV State. But it is more complicated than just driving. To trigger the parameter that activates the MAX EV State likely requires multiple other factors besides highway driving... like the HV Batt needs to be between 77-104°F for multiple drive cycles in a row and potentially measuring a certain level of Internal Resistance from the Hybrid Battery as well.

I believe the parameter that triggers the MAX EV State is similar to a Drive Cycle Parameter. The Prius needs to meet certain parameters for multiple drive cycles in a row for the Hybrid Control ECU to engage the MAX EV State. Once the parameters are verified it engages the MAX EV State and stays this way until another 12v disconnect or ECU reset.

I'm making a video on this presently after trying everything over the summer to get my Prius to re-engage the MAX EV State including installing a Project Lithium Battery... I've been stuck in the WEAK EV State for 3 years and 50,000 miles now.

I will explain the MAX and WEAK EV States as best as I can in short concise video form and it will all become much more clear. I technically can't prove them yet as I can't directly show the different behaviors between the MAX and WEAK EV States... but there is plenty of evidence from other posters that point to their existence.

Here is a preliminary test video I made earlier this year to showcase the WEAK EV State:

This video shows the WEAK EV State only. It shows the relationship between Pedal Angle, HV BATTERY SOC, and when the engine kicks on.

For the MAX EV State Pedal Angles would be much higher before the engine kicks on at the same SOC's as the WEAK EV State video above. But I can't show that for comparison because I haven't been able to record data for the MAX EV State.

This was just an initial test video. I will have much more info in the final version and have a well written narrative that makes a good argument for the existence of the MAX and WEAK EV States. This may be laying the ground work for a massive lawsuit against Toyota but that is not my intent.

I am working on the final video now as we speak:

Also user @Darklandscape just to keep you updated.
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You may have not proved it all out yet… but you are onto something that is really happening in my 07 Prius… since 12v battery disconnect a few moths ago. My city mpg is around 38 and above 40 mph… mpg is in low 50s… complete opposite of advertised performance. Gas pedal above 10-15% … kicks ice on… even with a nearly full charge battery…
Love to hear the finds of this theory….
Frank

Attention Prius Owners, I believe I have discovered a previously unknown Mechanism of Low MPG.

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Attention Prius Owners, I believe I have discovered a previously unknown Mechanism of Low MPG.

Mendel Leisk Senior Member

Troy1994 New Member

Frankusa94 New Member

Frankusa94 New Member