I'm confused about S4 mode ????????

If your driving non stop you don't really need to be in S4. S4 is only really useful if your in city driving or your trying to pulse and glide.

And yes the only way to get into S4 is to come to a stop and let the engine run for 10 seconds.

 

It seems there isn't. I tried many times. You can drive 100 or more miles and warm up your engine to the edge of explosion, but you won't get into the S4 ops unless you stop with the engine running and wait until it stops. I don't know why it is implemented this way, and I asked here at the PC and the techs in the Toyota dealership - nobody was able to give me a valid answer.

Apparently, the gen III Prius behaves differently, if I can judge from a test drive I had - I didn't notice that behavior. Perhaps the gen III owners could tell us how their cars behave?

I would be really grateful if anybody could ever explain me why is the S3-S4 transition working the way it is, as it really annoys and puzzles me all the time I have to drive wastefully in the 3a mode, unable to stop because of the traffic...

 

You should note that S1-S4 is not Toyota terminology, it is our terminology. So Toyota people won't know what you are talking about if you say S4 to them. Toyota won't say why and no one here is figured it out why the S3-S4 transition is the way it is.

So there is no why, it just works that way in the Gen II.

If you would install an EV switch, you can force the ICE to go out below 34 MPH just like you are in S4 anyway.

 

Well, I would dare to respectfully disagree. I often find myself diving wastefully in the city in the 3a mode, unable to stop for a relatively long time because of the traffic. It is really annoying. Especially when I finally come to a stop at lights and the green shows *before* the engine stops - that really makes me mad, as I have to go because of the cars behind me before getting into the precious S4 stage...

If I feel the transition is just about to occur, I even wait for that additional second or two when the green shows up, making the drivers behind me mad, not knowing what am I waiting for .

 

I didn't tell them about the "S4", I just explained them what I meant and they knew what I am talking about, but also didn't know the reason.

There *is* why. This simply puzzles the engineer in me - I *have* to know . This car is an engineering marvel, there *has* to be a reason, however bizarre .

I have the EV switch (it is a standard feature here in the Europe), but it is not helpful when I want to P&G...

 

If you're driving below 34mph during the 100 miles trip, you're always at S3a and the ICE continues to run.
If you're driving above 34mph, you're at S3b and it's identical to S4.

If your coolant temperature is above 66C(150F), following sequence will reach you S4 instantly;

• power off
• wait for 5 seconds
• power on

However, it's hard to accomplish the sequence during non stop driving.

Ken@Japan

 

Yes . . . remember in Detroit? Otsuka-san, the chief engineer looked like we were from mars when the S3-S4 transition topic came up ... and the 'why' question was asked. I thought that would be the defining moment in understanding what that is all about ... to no avail.

 

Well, my own experience is a little different. If I was driving faster than 34mph and I slowed down, my car would maintain the S3b until the ICE has to run. So, for example, if I am in the s3a, accelerate and get into the S3b and then slow down again, I can run on electricity under 34mph as long as: a) I don't stomp on the accelerator, forcing the ICE to kick in, b) the SOC doesn't drop below a certain level. Only when the ICE kicks in for whatever reason, the car engages the S3a again - that is how my Prius behaves.

Well, as you said, this procedure does not help much, does it ?

Ken, you know the Prius forward and back and have a lot of insider info. Do you possibly know what are the technical reasons behind this? It is torturing my curiosity since the day I drove the Prius for the first time .

 

Oh, looks like we'll never learn the truth then... This is one of the PRINCIPAL questions that have been torturing the humans from the very beginning! "What is the Purpose of Life?" "Is there a God?" "Who *really* killed Kennedy?" "Why is the S3-S4 transition in the Prius implemented the way it is?"

 

The idling check is done for 5-10 seconds during slowing down on the gen III, so the gen III does not required a complete stop for the S3->S4 transition.

You're a good candidate for the following DIY hack.
http://priuschat.com/forums/gen-ii-prius-modifications/36342-another-thermistor-hack.html

In our group at the Detroit event, Otuka-san clearly explained it's idling condition learning process to calibrate sensors.

I think your experience is same as mine, but you explained more detail.

Ken@Japan

 

Arigato gozaimasu, Ken-san

I am aware of the thermistor hack, but I still have some mixed feelings about it... It's a little dirty solution. If only the Prius was sold under the GNU-GPL licence ! Then we could all play around with the firmware freely... I want an open source car !

So sensor calibration... Interesting. I'd *love* to know more details, but I guess I am asking too much . Still, thanks a lot, Ken!

 

Yes but I still to this day can't understand what impact it would have on emissions if S4 were simply achieved via temperature ... without stopping / restarting.

 

I think no one asked question about the emission impact in our group.

Ken@Japan

 

I found this trick by accident ! It even seemed to work if the interval is just 1 sec.

Another thing I noticed: S3 mode with battery SOC >60% behaves like S4, but falls back to S3 behavior once SOC falls below 60%.