1G Toyota EPS with vehicle speed sensor input?

[Drewpy Dawg]

I know some people here have done the Toyota electric power steering swap. It’s not something I’m planning to do until my car is running and driving, but I’m thinking ahead about the possibilities.

None of the installs on various cars that I have seen online use the vehicle speed input to the steering ECU, and therefore the steering is in full assist any time the ECU is powered on. From what I have found searching it appears the speed signal to the steering ECU is just a PWM signal, like our OE vehicle speed sensors produce. It seems to me that it would be very easy to add a VSS signal and get the speed sensitive steering that the factory built into the ECU. You could even manipulate the PWM signal to dial in exactly how much assist you want at low or high speeds. Full assist at parking speed but tapers off very quickly once rolling leaving you with the full feel and feedback of a manual setup. Tapping into our stock VSS would be trivial.

Has anyone done this on their EPS install? Anyone know any reasons why it wouldn’t work or why it’s “not that simple”?

 

[jdxnc]

I don't know of anyone who's done that exactly but I know there's a module you can purchase on ebay with a potentiometer that can vary the assist and I've seen one that uses GPS speed.

The pulses per given distance between the Mitsu sensor and the Toyota sensors might be quite different or very similar, I don't really know. On my car with the Fueltech ECU I found that 5 pulses of the oem 2g speed sensor is equal to one tire rotation, perhaps that data could help someone trying to figure this out.

 

[Drewpy Dawg]

If we can find out what pulse width the Toyota steering ECU is expecting at various speeds (a chart or graph would be great) then it would be pretty easy to program an Arduino to intercept the VSS from our cars and output an analogous signal that the EPS could use and get the full variable assist experience. Could even add a potentiometer to adjust the overall amount of assistance, like a global setting, rather than just a knob you adjust and get that amount of assistance at all speeds.

Anyone here know any Toyota techs that could get that kind of info?

 

[Justin DuBois]

Someone here has Toyota Prius electric power steering.

 

[Drewpy Dawg]

Yeah, I know there are at least a few here, but all the installs I’ve seen just have the steering ECU powered up to give one constant level of steering assist at all times. In the Prius the system uses vehicle speed to determine the amount of steering assist. I want to figure out how to do that in our cars so we can have full power assist at very slow speeds, like parking, but little to no assist at higher speeds when it’s not needed, thus leaving the steering with full manual feel.

 

[Bedicine]

Any updates on this?

 

[Drewpy Dawg]

Unfortunately no. I've done a lot of searching but can't find a definitive answer. It appears that nearly everyone who has done this on various cars is just using it in fail safe mode. Some sources say the EPS just needs a 5 volt square wave signal, others say it has to be a specific CAN signal.

 

[curt-s]

Any potential to tag along with somebody in Toyota with one of these sensors and, while using a portable oscilloscope, log the pulses and speed?
An uninterruptible power supply and a regular oscilloscope also works in a pinch. The better ones have canbus decoding..

Just a thought

 

[Drewpy Dawg]

Exactly the data we need. If only I knew someone who had a Toyota with EPS.

 

[Vettefan65]

I've been looking at this issue. About a year ago, I installed a Prius EPS unit under the dash of my 79 Corvette. When there is a CAN bus failure, it defaults to the speed of 43MPH. Its a little more steering assist than I'd prefer. I'd like to take the vss signal and send it to the EPS controller as you have suggested. If it helps you figure it out, here is a link to the repair manual for a 2006 Prius. It delves into the nitty gritty... https://attachments.priuschat.com/attachment-files/2019/10/175907_Power_Steering.pdf

 

[Drewpy Dawg]

I'm bringing up this old thread because I found the info I was looking for. A post on a Suzuki Samurai forum lays out how to do it using an Arduino, a CAN bus shield, and some code. I won't copy it all here, just the link to the original post. It's an older post and a bunch of the images no longer work, but the info is there in text and the text file attachments with the code are still available.

EPS202

There were brought up several questions about adjusting the sensitivity of the EPS after my EPS101 write up. We are going to correct that in this howto. At this point it is assumed that you have completed EPS101 and have a Yaris EPS functioning in limp mode when you turn the key on. Note...

bbs.zuwharrie.com

This was the second of three posts about the EPS. The first was just about physically mounting the EPS in his Samurai, and the third was how he used a GPS module connected to the Arduino for a speed signal rather than a VSS.

Finding this motivates me to get the parts to put EPS in my Talon (when I actually get it on the road). I hope it helps others.