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Power Steering using Toyota MR2 EHPS pump

223270 Views 72 Replies 39 Participants Last post by  remy_martian
Many EV conversions have to deal with Power Steering decision. If you decided to keep PS and looking how to drive PS pump, consider this all-in-one solution brought to you by Toyota engineers. Toyota MR2 has EHPS ( Electric Hydraulic Power Steering ) in which pump is driven by its own electric motor instead of pulley hanging off the main engine like most ICE cars do. First generation of MR2 had separate fluid tank, motor/pump assembly and controller, some EVers took motor/pump and wired it directly to 12V or via various switching circuits designed to keep the pump off while driving straight or at high speed to save power.

However, 3rd generation of MR2 also called Spyder has a single pump assembly combining motor, pump, fluid tank and controller, making it very attractive option for EV community.

To the best of my knowledge you are looking for 2000-2005 ( maybe some other years, I'm not sure ) EHPS pump from Toyota MR2 Spyder, call your local junk yards or check this one online . The pump looks like this:

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To wire it use schematics below. If you don't have proper harnesses you can either solder directly or create your own connectors for each pin. I personally created connectors and then filled harnesses with caulk to keep wires in place. It can be removed later if needed.

Passive circuit component Circuit component Diagram Plan Technical drawing
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Although 50 Amp relay is stated, I couldn't find one so I used typical 40 Amp automotive relay, my testing shows that it doesn't actually reach 50 Amp current anyway.

You can wire VSS signal from your car to make the pump turn itself off at higher speeds, but I couldn't manage that because my Miata has unusual VSS signal. Even without VSS, the pump runs idle at 4 Amps until you actually turn the steering wheel, so the power wasted is very minimal.

You'd have to find a way to connect PS Pressure line from the pump to your car's rack and return line from the rack back to the pump. Return line is easy, just use 3/8 hose and clamps. As for pressure line, if you are lucky you can fit one from other Toyota models, if not, you can make custom one from separately purchased fittings and the pressure hose, I have seen those on Ebay and online shops like this one

Hope this helps, feel free to update this Wiki with more details, my main goal was to publish schematics and wiring, I am not very good with hydraulics, maybe someone can add details on making custom pressure hose.

Here are the Toyota part#'s for the electrical Connectors: These part#'s get the Plastic part only, The metal pin wiring parts are sold separately. Maybe someone can add the part#'s for those.
Part#'s Large connector 90980-12068
Middle connector 90980-10897
Small end connector 90980-10942

There are two part numbers for the wiring. They come with the plugs, rubber seals, & about 6 inches of wire. At $6.55/ea they aren't cheap for what you get, but they are made to fit.

Three pigtails for the small & middle connectors P/N: 82998-12440
Two pigtails for the large connector P/N: 82998-12500


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look at original pinout from Toyota on the other picture, pin 5 is under pin 1, and pin 8 is diagonal from 1. My wiring diagram is a mirror image because I am showing harness on the pump, not the connector, but still 5 is under 1.

And I don't think my pump would be working if I had it wrong...

you missed the point of this connection, its not supposed to be ground, its a control line from controller to relay. If it was ground then relay would be always on, then you don't even need the relay, just apply power constantly.

Using this line controller has ability to shut off power to the motor completely by raising this line, for whatever reason ( protection, overheat, speed signal, etc. ). Under normal condition and during the start this line is low, which allows relay to trip. If you are checking continuity by ohmmeter, do not expect this line to be ground, its not supposed to be.

Just try and connect everything as it states on diagram, I promise that relay will trip and pump will spin.
Are all connections solid when you apply power? For example I wanted to measure relay current and I applied controller power first, then hooked ammeter to relay afterwards. This failed because controller didn't sense relay circuit and didn't close it. Make sure whole schema is connected prior to applying power.

Otherwise I don't know what to say, I didn't come up with this schematics, it came from Toyota, you can clearly see it on attached diagram.
I don't think original Toyota design uses steering sensors, there is no need for it if you use speed signal, which is marked VSS on the schematics. If you get VSS from your car connected to the pump, then it should stop running after your car reaches certain speed where PS is not needed. All this is theory for me because my car doesn't have compatible VSS signal, so my pump is running at all times.

Also, consider the power it takes to run idle is less than 100 Watts, which is miniscule compared to what main motor uses, does it really matter if your pump never stops running? PS pump would use 0.1% of your total battery power, is it worth complicating things with a dashboard switch? In case of emergency road condition where you will need to steer quickly, will you have time or even remember to flip the switch? I don't think so. I have been running PS pump for 4 months now, I see no impact on batteries or range, pump is idling when you drive straight, so why bother switching it?

Hope this helps.
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