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

It is not that your 2020 Corolla Hybrid that was serviced now Drags and has Less Power... What has happened is that the Corolla Computers have changed what Pedal Angle activates the engine... where before EV Mode would have been used instead for the same HV Battery State of Charge.

Your 2020 Hybrid Corolla is still delivering the same amount of power as before the 12v disconnect... But it is now substituting Engine Power for what was previously provided only by EV Mode via the HV Battery prior to the 12v service.

Basically, parameters in your Hybrid Corolla ECU's have been reset that tell EV Mode to be used aggressively at City Speeds (0-50KPHish). It now runs the engine in place of EV Mode for power.

You are describing the WEAK EV State nearly word for word.

The reason you get better L/100Kms while country driving because above a certain speed, the engine needs to run all the time to protect the transmission. At this point differences in drivetrain behavior cease between the MAX and WEAK EV State and L/100Kms will be the exact same as the drive trains deliver power in the exact same way. L/100Kms for city speeds are only what's effected... not highway speed L/100Kms.

To get the MAX EV STATE to reactivate permenantly... you will likely need to do multiple drive cycles in a row of highway commuting under ideal conditions for the Hybrid Battery... as the hidden drive cycle parameter that regulates the EV States is needs specific information from the Hybrid Battery to decide that your 2020 Hybrid Corrola can safely activate the MAX EV STATE and use EV Mode aggressively again at city speeds.

Also, an update for anyone interested:
I'm still working on proving this issue definitively. Hopefully by Summer's end I will be able to show everyone exactly what I'm trying to explain in this post if I'm able to gather the data I need. I just need to get my Prius to engage the MAX EV State so I can record it's data.

The WEAK EV State Data is recorded in this YouTube video for anybody interested.​

 

Update: I am still hard at work trying to expose this low mpg mechanism... but am failing on my own. In the end, I will need help from the Prius Community to prove it.
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Since my last post, I have bought a 2nd 2008 Gen 2 Prius with 127,000 miles and installed a brand new OEM Toyota Hybrid Battery in it and have attempted to get the MAX EV STATE to trigger by doing lots of highway commuting.











I have failed to get this 2nd Gen 2 Prius to trigger the MAX EV STATE despite having a brand new Hybrid Battery. I have hard pivoted to making a 2nd comprehensive post about this issue as well as a video to describe it. I wanted to be able to show exactly what I'm talking about... but I can't get the MAX EV State to trigger on either of my Gen 2 Priuses. To show what I'm talking about I will have to test a MAX EV STATE Prius first.

Once I complete the video, I will have a clearly devised way that anybody can test for the MAX and WEAK EV State with relative ease as long as they have an Android Smartphone/Tablet. The second comprehensive post I make will be much more clear, concise, and well thought out. The only way I'll be able to prove the MAX and WEAK EV States for certain is by getting the data from a MAX EV State Prius/Toyota Hybrid, which will likely have to come from the Toyota Community at this point.

For now here are links to Imgur Posts with highlighted text of every Priuschat Post I could find describing this low mpg mechanism:​

High Accuracy Priuschat Posts that describe the WEAK EV State:​

Gen 2 Prius:

Hybrid System Less Efficient After 12V Disconnect/Battery Change? ECU's? (My original post)

Beware of Dealer ECU Calibration MPG way down

2007 "poor" gas mileage

Significant reduction in MPG between 2004 and 2005 Prius'
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Gen 3 Prius:

Possible undiscovered performance and MPG issues with Prius v (lowercase v)(This post solidified that the WEAK EV State was real and potentially widespread)

Does the car remap or recalibrate the HV battery?
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Moderate Accuracy Priuschat Posts that describe the WEAK EV State:​

Gen 2 Prius:

2008 Prius MPG dropping like a rock after new 12v battery and coolant pump change

Dramatic mpg drop after service

Gen 2 with 220K miles, sudden 10 mpg loss, 12V battery?

Need Help!! 05 Prius Just replaces hybrid battery recently! MPG is terrible.

Prius Sudden Fuel Economy Decrease

Problem with electric motor or hybrid system?

REGEN COMPUTER FAIL DROPS 5 MPG

Sudden drop in fuel economy

Wheel bearing cost me 7-8mpg?

When does the electro motor kick in?​

Gen 3 Prius:

Mpg from 45 to 38 to 30 all in two weeks

Hybrid Assist Issue / Poor City MPG

Latest Software Update Safety Recall Resulting in 8mpg less...

Lost 10mpg after EGR clean, etc. Now losing mind!

Lost 10mpg After Replacing 12V Battery

MPG 4MPG lower after Software upgrade/Recall

Poor Fuel Economy After Brake Change

Prius less aggresive after battery relative campaign?
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LA Times Article about a 3rd Gen Prius Owner experiencing the WEAK EV State:​

Toyota Prius software fix may reduce fuel efficiency, experts say

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Also for the video I am making about this... I've made a meme from The Matrix scene where Neo becomes the one. It is going to go in the final video somewhere but not sure where exactly yet. This is the rough draft and subject to change:

Featuring:

@kirill626
@bisco
@Mendel Leisk
@mikefocke
@TheLastMojojomo ​

 

Just a quick update, I am still working on my final post and have made a few graphics to better explain the EV States:







My Final post will hopefully be done soon. I am waiting to receive the correct electrical connectors to install the EV Mode button in my American Gen 2 Prius to see if that increases EV Mode Output similar to the MAX EV State when the button is pushed.

All Images Below measure the WEAK EV State Only:

Below is the behavior of the WEAK EV State when the HV Battery is charged above 75%















Below is the behavior of the WEAK EV State when the HV Battery is charged to 74% but not above:












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A Small update:
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I have since installed the EV Mode button mod in my American Gen 2 Prius and it has allowed my Prius to use EV Mode aggressively like the MAX EV State and finally has given me a coherent way to show exactly what the MAX and WEAK EV States are.

Below is with the EV Mode Button pressed simulating a "Pseudo MAX EV State":


Below is the WEAK EV State:


You can see in the WEAK EV State the Combustion Engine turns on and completely takes over power output while EV Output is virtually non-exist.

The MAX EV State essentially makes the Prius behave like the EV Mode button is pressed in all the time when under the right condition... SOC, Battery Temp, Speed, etc. There are still nuances and such but I will have the well fleshed out in my final post.

I will be posting a tutorial on the EV Mode Button Install and likely some preliminary videos regarding the EV Mode Button and comparing it to the WEAK State while I'm working on my final post.

I have also made a quick tutorial on how to download chart files and test your Gen 2/Gen 3 Prius with charted data exactly as I have done above in the screenshots using the Android app Torque, and an Add-on app called Realtime Charts for Torque:​

This YouTube Tutorial was addressed at PriusChat user @Darklandscape as he has shown great interest in the EV States and has been privately messaging me about the WEAK EV State for over a year now... but the tutorial will work for anyone.

Here is the link for the files in the Tutorial to test your Prius for the WEAK or MAX EV State.​

 

No it has nothing to do with the stage 3a/3b to stage 4 of engine warm-up. It is the EV Output allowed that changes when comparing a WEAK EV State Prius to a MAX EV State Prius.

At 60% SOC... a WEAK EV State Prius will only use 13hp EV Output before kicking the engine on despite being in stage 4 of Hybrid Operation.

At 60% SOC... a MAX EV State Prius will use 28+hp EV Output before the Combustion Engine kicks while also being in stage 4 of Hybrid Operation.

Below is the graphic attempting to explain this:
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In the YouTube videos I've posted above.. my Prius is in stage 4 of Hybrid Operation... you can tell this because the engine immediately kicks off as soon as my foot leaves the gas pedal. This is the tell tale indicator for a successful transistion from stage 3a/3b to stage 4... which requires a Calibration shutdown at a full stop once the ICE Coolant reaches its optimal temp.

After the stage 4 Calibration shutdown... the ICE will shut off immediately as your foot leaves the gas pedal... as you can see in the 1st 30 seconds of the YouTube video below. You can also hear my radiator fans running to cool the engine proving it's at least at 200°F:

So for example... what you see at timestamp marker 22:58 in the video... which is a recording of the WEAK EV State... EV hp Output is only allowed to be 19hp at 70% SOC.... before the Combustion Engine turns on.

In this exact same scenario for the MAX EV State... EV hp Output would have been allowed to be 28hp+ at 70% SOC... before the Combustion Engine turns on.

So if you watch from 22:25-23:00 in the YouTube Video I created above and I were in the MAX EV State instead... the yellow line(Instant EV hp Output) would travel at least to the orange line(28hp - Max Ev Hp Output allowed according to the WOUT parameter in the Hybrid Control ECU) before kicking on.

And both of them would have been in stage 4 of Hybrid Operation. This extra EV Output also applies backwards to the other stages... like stage 2 where the Prius coolant is not optimal temp yet... but the ICE can still shut off if standing still long enough. The initial burst of acceleration even in stage 2 will provide more EV Output in a MAX EV State Prius compared to the WEAK EV State.

What pressing the EV Mode button does is... it shows how much more EV hp Pwr the Prius is capable of producing and is a "Pseudo representation" of the the MAX EV State with some stipulations. It allows a similar level of EV Output and makes my Prius use the same level of EV pwr that it used to when it was in the MAX EV State.

If you'd like to review the high accuracy posts that describe this WEAK EV State phenomenon to a T by the few Prius owners who were trying to wrap their head around this problem.. those are below:

Hybrid System Less Efficient After 12V Disconnect/Battery Change? ECU's? (My original post)

Beware of Dealer ECU Calibration MPG way down

2007 "poor" gas mileage

Significant reduction in MPG between 2004 and 2005 Prius'
Gen 3 Prius:
Possible undiscovered performance and MPG issues with Prius v (lowercase v)(This post solidified that the WEAK EV State was real and potentially widespread)

Lost 10mpg after EGR clean, etc. Now losing mind!

Does the car remap or recalibrate the HV battery?

Also here is a better post describing the stages of Hybrid Operation.​

 

It can be two different Prii or the same Prius in the MAX or WEAK EV State.



The MAX and WEAK EV States are "Phantom Software States" in the Hybrid Control ECU that dictate EV Output. Since they're software... any Gen 2 or Gen 3 Prius can be effected by them. (And possibly Gen 4/5 but I have no strong evidence for that yet).

Most people who notice the WEAK EV State have driven two different Prius side by side... one in the MAX EV State and the other in the WEAK EV State. They notice significantly less City Mpg and the engine revving more... or what they describe as "loss of power".

You can also notice it if you have a very analytical mind analyzing your own Prius behavior or if you drive your Prius hyper specifically like me. (106 mile mail route, 400 mailboxes, stopping at the same place and driving in the same way and speed every day. Used to get 45mpg on mail routes now get 35 due to the WEAK EV State and have lost $3,000+ in gas over the past 7 years.)

The "WEAK EV Software State" is triggered by a 12v disconnect... which defaults the Prius to the WEAK EV State automatically as a result of the Prius ECU's losing their memory... Likely as some sort of protection mechanism for the Hybrid System but im not really sure.

And the "MAX EV Software State" appears to engage after multiple drive cycles in a row of highway commuting... which was my experience in the past... But sometimes this seems to never happen and the Prius becomes permanently stuck in the WEAK EV State... like my Prius has been for 3+ years after a 12v disconnect.

The multiple drive cycles in a row of highway commuting likely allow some sort of Calibration or Hybrid System self check to be undergone... and when that self check/Calibration recieves a pass condition... the Prius permanently persists in the MAX Ev State until another 12v disconnect. The behavior is similar to passing emissions monitors and may actually be directly related to emissions monitors.

My whole reasoning for the WEAK EV State existing as some sort of protection mechanism makes less sense now that the EV Mode button makes my Prius behave like the MAX EV State. It may actually be a glitch of some kind that causes the WEAK EV State to chronically persist and never engage the MAX EV State... but I'm fairly sure the WEAK EV State exists for a reason still... it's supposed to be a normal part of the Software Programming.

Think of the EV Mode button as a "Forced Software State" that causes the Prius to use EV Mode very aggressively by pushing a button... while the MAX EV State is a "Master Phantom Software State" that is supposed to trigger from reading other prius computer parameters and verifying certain conditions. It exists omnipresently in the software and during all driving conditions once triggered. Once it triggers... EV Mode has very aggressive useage between 3-8 bars of charge and up to 40mph for the Gen 2 Prius.

The reason no one has ever identified this as a serious widespread issue... is because it's completely phantom. You could even be in the WEAK EV State right now @dolj and you'd have no idea.

No error code or way to view this parameter/software state makes itself known in Toyota Techstream... so when you take your Prius to the Dealer complaining about sudden low mpg or loss of EV Power... they'll hook up Techstream and everything will seem perfect. They'll say you need to hypermile or it's bad gas or something to that affect.

I believe Toyota has already been sued for the WEAK EV Software State... but the cause of the Low mpg/engine running more was misplaced.

In the LA TIMES article screenshots below... multiple Prius owners complain of having low mpg, the Combustion Engine running more, less EV Power after the Hybrid Control ECU update to protect the Inverter.​

The Prius owners complained of low mpg and differences in drivetrain behavior after the update... leading to lawsuits against Toyota





Toyota then issued A statement that we don't believe the software update should significantly reduce mpg... and they were technically right.

The loss of mpg and EV Output as a result of the Hybrid Control ECU update... was not a direct result of the ECU update... but an indirect result of the computer reset that occured during the process... resetting the Prius to the WEAK Ev Software State.





So this WEAK EV State Software that was already latent in the Hybrid Control ECU... and exists outside of the Hybrid Control ECU update that was issued... was activated during the update.

Toyota and the Prius Owners that were effected by this... were looking in the wrong place in the software for the cause of the Low mpg. The Prius Owners were not wrong that they were experiencing lower mpg and different Hybrid Drivetrain behavior after the software update. It's just that as a byproduct of the software update... the WEAK EV State was triggered.