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Power Steering using Toyota MR2 EHPS pump

223261 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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While hooking up my pump I found a small yet important mistake in your diagram. The ground that feeds the relay from pin five on the middle plug (pump) is actually the bottom left pin instead of the bottom right. The pin that you indicate is actually pin 8.

Thanks for the great work!!

Ben in SC
You're right about the pin numbers. My mistake. But, I have ground on pin 8, 5 doesnt give me any connectivity to ground. I dunno but thats how mines working and thought I would point it out for other.

Still just awesome work, Dimitri.

Okay, I guess I really need some help. Hope your around this morning.

I hooked everything up per your drawing (assuming I understand the relay symbols) and I cant get it to work.

Heres a breakdown:

Relay pin 85 to 12V
Relay Pin 86 to pump pin 5
Relay Pin 87 to 12V
Relay Pin 30 to pump Pin1 (next to gnd)

Pump pin 5 to switched 12V
Pump pin 2 to ground

Am I anywhere close? It seems that I never get the relay to close with the relay switch side ground connected to pin 5. I'm hoping that I have something wrong. As I mentioned earlier, and I understand what I was doing wrong, I can get the relay to close by connecting to pin 8 as it is directly tied to ground.

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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 went out and confirmed that I have 12V to the relay before connecting the switched 12v to pin1. I guess I'll just have to wire it directly and bypass the controller.. At least it does work that way.

Thanks for trying to help me.

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