Prius Gen 2 EPAS - Electric Power Assist Steering

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Prius Gen 2 EPAS - Electric Power Assist Steering

Post by Gregski »

thought you would find this video interesting, not mine, but good info


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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by imwoody36 »




and this is my own version, with wires shown from 2013
the priustoric boatcar guy
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by arber333 »

I will go off the reservation here to comment on rivnuts... the circular type is rubbish. Wouldnt trust it to carry any serious load.
Now hex version is very different... when drilling out the hole you need to file that into hex shape, but when it fits you can just tighten it with one bolt. It is made for multiple dissassembly and i have seen them on various OEM cars.
https://www.rivetnutusa.com/hexnut-hex-rivet-nut/
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by Gregski »

yeah sure, but does your video even have a dirty sock in it???
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by mark »

Gregski, you inspired me to create a wiki page, with links to this thread as well as your posts from the project thread.

https://openinverter.org/wiki/Toyota_Pr ... t_Steering

I was going to upload some of your pictures of the EPAS unit from your project thread, but it asks you to verify that the pictures are your own work, which wouldn't have been true.
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by Gregski »

mark wrote: Thu Sep 22, 2022 1:12 am Gregski, you inspired me to create a wiki page, with links to this thread as well as your posts from the project thread.

https://openinverter.org/wiki/Toyota_Pr ... t_Steering

I was going to upload some of your pictures of the EPAS unit from your project thread, but it asks you to verify that the pictures are your own work, which wouldn't have been true.
wow, that's amazing, and yes I try to give credit whenever I "borrow" stuff from somebody else but I also do not let it stop me from using others material for demonstration, education, and learnization, since I do not profit from it in any way I sleep well at night
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by MattsAwesomeStuff »

Always a big supporter of content being added to the wiki.

The next hurdle is... making sure people can find it on the wiki, which right now is a challenge. Unless you specifically know to search for it, how would you ever come across it?

I keep meaning to try to rearrange the whole wiki into a more organized set, but, have been too intimidated to start. :/
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by Gregski »

so I decided to mount the control box for this thing today and thought you mind find some of this content useful, for instance we can easily remove the lid off of the module and that allows us to flatten those silly OEM brackets on the back of it




IMG_4356.JPG
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"I don't need to understand how it works, I just need to understand how to make it work!" ~ EV Greg
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by xp677 »

Did anyone ever figure out the CAN messages for these? I've got one as well, IIRC the current method has to just let them time out and go into a failsafe mode, which gives basic control, but you lose functions such as variable assist.
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by MattsAwesomeStuff »

xp677 wrote: Tue Jul 18, 2023 7:44 amthe current method has to just let them time out and go into a failsafe mode, which gives basic control, but you lose functions such as variable assist.
IIRC, the current mode defaults to the amount of power steering you'd get at 40mph. So, less than it would've given you in a parking lot, but more than it would give you at highway speed. It is variable, it's not just overpowering and slamming you without any wheel feel.

I thought I saw someone who'd partially figured out the CAN for this, but I forget where (not in this community, someone on their private build).
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by WacoKid »

Hey Matt, I have been investigating the Prius epas for a setup on my 64 C10 and have seen some people mention feedback about issues and that the EPAS is not allowing for a proper return to center(RTC) after cornering, in the context that it's not working or not working well enough. It varies from forum to forum so no real way to tell how much is exageration vs real issue. I am doing a setup on a lifted 2wd truck, not exactly a viper but hey, we all love our projects. It will have 32 inch tires so obviously the steering not returning to center would a definite driveability issue. I've got the epas box and controller but hanging on buying the manual or powered gear box based on what info I can find out about the RTC issues. I suppose my real question is since you have had your Jag running with the EPAS have you noticed it or has the issue shown itself? I'm unsure if the weight of a car would change the tendency for it to happen but it may? Some reported they thought it had to do with the module not receiving feedback from VSS or steering angle sensors. I'm also looking for answers about adjusting the strength/sensitivity but seems like answers are still lacking
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by MattsAwesomeStuff »

WacoKid wrote: Wed Jul 19, 2023 4:56 pmHey Matt
Wrong Matt.

That Matt doesn't hang out here and I don't know him. Also I'm like, 10% as cool as he is and only half as smart.

I wonder to what degree the lack of self-centering is related to vehicles that were formerly manual-steer, or had wonky steering trail.

I guess a super strong power steering would give you no feedback from the wheels (as feedback is basically the wheels not going where the steering wheel is telling them to go), and thus no self-centering. My super-super-super half-assed solution would be to wire a bunch of 20A diodes in series with the power steering motor to bleed off voltage and weaken it so that it doesn't overpower the vehicle's steering trail.
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by WacoKid »

Silly me for assumingl. I had my hopes up I had a pipeline to the man himself. Anywho I was thinking perhaps that if the default assist is around 40 % there is probably a default level of torque resistance which would cause the erratic RTC, or perhaps there is none at all. I'm no engineer at all, more of a cobbler. I can't recall where it was I saw the questions and complaints it but was across a myriad of google searches and in one result there was some discussion back and forth on lighter cars and old guys with bad shoulders saying how hard it was to turn their 1.5 wheel lock to lock high ratio rack and pinion setups and failure to RTC when trying to get it on and off the display racks and test driving. Must be terrible.

Looking back I found a more relevant search in the ls1tech forums regarding what they were calling a Yaris module but judging by info and pinouts this is also the Prius model from what I can see on the outside. Looks like they have a little relevant data about canbus info but also some comments about return to center issues because there is no reset of the zero point of the steering angle sensor.

https://ls1tech.com/forums/suspension-b ... ues-5.html
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by Gregski »

WacoKid wrote: Thu Jul 20, 2023 1:39 pm Silly me for assumingl. I had my hopes up I had a pipeline to the man himself.
Guilty of the same crime myself!
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by WacoKid »

I was laying in bed last night and the EPAS question has been lingering in the back of my brain so I was cruising through Ytube and found a rather recent video where a fellow engineered his setup for a F100 pickup and he shows a GPS oriented device that fills in the variable speed portion for the Prius setup. It seems viable and I was pretty excited to see this info initially but after looking through his comments he stated that the GPS speed caused some erratic behavior and he ended up unplugging it and was fine with it as is. Here is a link to the video:

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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by MattsAwesomeStuff »

Add that to the wiki. And the note about how if you remove that bracket you'll bottom the bolt out against the gearing, and need to use a washer to avoid that.
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by muehlpower »

i have no idea about the prius steering, but on mine, from an opel corsa, the steering assistance is given by two square-wave signals. One corresponds to the engine speed, taken from the ignition coil. It must be at least 800RPM, 4 cyl. so that a steering support occurs. The other is the wheel speed from the ABS sensor. The higher the frequency, the lower the support.
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by Tuff »

Hey, just joined to give you guys some help. I figured the can thing about a year ago. It's not as hard as you guys think it is. Here's a link to my build tread which has the code you can copy paste and get your EPAS working. It seems like you guys are archiving this info so I hope it helps anyone else in the future.


https://www.toyotanation.com/threads/88 ... t-14730373

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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by mane2 »

I'm struggling with lack of return to center with my Citroen C2 EPAS. I have it working (in non-failsafe mode) with RPM and Speed info sent via can bus. Speed info is coming from another bus and sending it forward to EPAS ecu, and it works well, except return to center. Car has a lot of caster, so that's not the issue and alignment has been done multiple times with different settings, trying to find the culprit.

I know the format of Citroen C2 steering angle sensor ecu message. I tried to emulate that by code, and check if it does something with steering but it did not. No matter what position the wheel is emulated to be. I also tested actual Citroen C2 with dual-can arduino, by blocking SAS (Steering Angle Sensor) information, and I did not notice any difference in steering.. It always returns back to center nicely. Though it's FWD car, so they tend to return better anyway because of the front wheels pulling.

I think C2 does not do any assist on returning to center.. So I need to find another that would. I found Mini R56 EPAS, and trying that out next. Not sure if it will do either.. Maybe Miata/MX5 could work, as it's RWD and narrow enough to fit my 70s car frame.

I've been trying to search for information about EPAS and SAS combination, but haven't found anyone that has actually achieved return to center with SAS signal. Would be grateful if somebody would have info related to this EPAS & SAS -combo with RTC (return to center) issue.

EDIT: Just found documentation which states "This steering system does not require input from a steering wheel angle sensor." for Citroen C2 EPAS. So I guess swap to something that uses angle sensor info is needed, to help return to center. Not sure if Mini R56 EPAS uses that,
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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by Gregski »

mane2 wrote: Thu Oct 05, 2023 5:56 pm I'm struggling with lack of return to center with my Citroen C2 EPAS. I have it working (in non-failsafe mode) with RPM and Speed info sent via can bus. Speed info is coming from another bus and sending it forward to EPAS ecu, and it works well, except return to center. Car has a lot of caster, so that's not the issue and alignment has been done multiple times with different settings, trying to find the culprit...
I just recently decided to tighten the steering box as it is called on my old Chevy truck, this removes the side to side play in the steering wheel so that you don't look like you are driving a car in an old 1950s movie. Anyway we were tightening it a bit at a time, maybe 1/4 turn of the adjustment screw and after we went a bit too far and the steering got too stiff, the truck no longer would return to center. Of course we backed it out about an 1/8th of a turn and it started returning to center again.

I don't know what sorta adjustments you can make to your steering column \ steering rack or box, but maybe look into that.


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Re: Prius Gen 2 EPAS - Electric Power Assist Steering

Post by mane2 »

In rack & pinion systems, there is only preload screw - which I hear, should usually not be played with, as they might start to rattle or bind. But worth of try if nothing else helps.
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