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

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.​

 

In the video I force charged my HV Battery to 80% by putting my foot on both the gas and brake simultaneously while in Drive. This is when my OEM Ni-Mh HV Battery read at 60% capacity according to Dr. PRIUS.

If the HV Battery is above 104°F... the Prius will not let you charge the HV Battery to 80% as it begins to throttle maximum charge allowed in after that point.

As long as your Prius HV Battery is below 104°F... you definitely can charge it to 80٪ SOC. It doesn't matter that your Battery capacity reads 50% in Dr. Prius. Your Battery is still able to attain the 80% SOC which is measured by voltage reading not charge capacity. The only thing the capacity test does is measure how long the HV Battery takes to discharge from 70% to 40%. Not whether it can attain an 80% SOC or not.

Fundamentally your not understanding what I'm attempting to explain with the EV States... and I don't blame you... My initial Post above is very Schizoy and somewhat incoherent. The video I'm making and 2nd post will be much more coherent.

I will try to explain simply what I mean by MAX and WEAK EV State.

Let's say your Gen 2 Prius has 6 State of Charge Bars on the MFD Display:



For a MAX EV State Prius, Gas Pedal Angles allowed for EV Mode will be much higher at 6 Bars SOC... around 60%+ of full throttle... resulting in much more EV power and acceleration in EV Mode and the the ICE Spinning up much later in normal city driving... allowing the Prius to get the 48 EPA estimated City MPG's.

For a WEAK EV State Prius, Gas Pedal Angles allowed for EV Mode will be significantly reduced at the same 6 bars SOC... around 30% of full throttle... resulting in much less EV Power and acceleration and the ICE Spinning up earlier and more frequently in City Traffic reducing city mpg's from the 48 EPA Estimated Mpg's to 35-40 MPG.

This EV State Parameter is dictated by what I believe is the Hybrid Control ECU in the Prius. The Hybrid Control ECU is reverted to the WEAK EV State after every 12V disconnect or ECU reset.

To get the Prius Hybrid Control ECU to revert back to the MAX EV State... a drive cycle style parameter needs to be undergone... similar to an emissions monitor.. but for the Hybrid System instead. If all the parameters are met for say 3 drive cycles in a row, the MAX EV State will trigger permanently until another 12v disconnect.

But Toyota has not disclosed what this parameter is, why it happens, or the engineering reason behind it. And it appears to be rather stringent... I believe right now there are 100,000's of Toyota Priuses/Hybrids on the road affected by this causing chronically low city mpg's.

My Personal Gen 2 Prius use to get 45ish mpg on my 106 mile 400 mailbox mail route I did everyday.

Then after a 12v disconnect, for the exact same mail route driven the exact same way everyday... my Prius now gets 35ish mpg and never more... due to being reverted to the WEAK EV State. My Prius has now been stuck this way for 3 years and 50,000+ miles.

EV Mode is much less aggressive than it use to be... and it happend directly after the 12v disconnect... and if you read the My Low MPG Story section of the original schizo post... my Prius has reverted between the MAX and WEAK EV States multiple times.

I have found 6+ posts from others that describe this phenomenon in coherent detail... and dozens more that I believe are attempting to describe this same WEAK EV State LOW Mpg phenomenon... the posters just don't have coherent knowledge of how Priuses/vehicles work in general to describe what is happening... all of this will be gone over in my final video/post.

For now... here are some photos for the final video/post I'm working on.

The screenshots below show the Maximum Pedal Angles allowed before the ICE kicks on in relation to HV Battery SOC for my WEAK EV State Gen 2 Prius:









You can see how the Pedal Angles before ICE Activation corellate directly with HV Battery SOC.

If this were a MAX EV State Gen 2 Prius, Pedal Angles would be around DOUBLE before ICE activation occurs...

Also note, the response curve for Pedal Angle/EV Mode changes between 0-15mph... resulting in a higher EV Mode Output and Pedal Angle for slow speeds in relation to HV Battery SOC.