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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 http://car-part.com . The pump looks like this:

Auto part Automotive engine part Automotive starter motor Carburetor Engine


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
Auto part Carburetor Automotive engine part Engine Vehicle


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 http://www.summitracing.com/

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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Dimitri,

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
 

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Discussion Starter · #7 ·
Ben,

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...
 

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Discussion Starter · #9 ·
Ben,

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.
 

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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.


Thanks!!!
Ben
 

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Discussion Starter · #11 ·
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.
 

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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.


Ben
 

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Discussion Starter · #15 ·
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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Do you know what adapter is needed for the high-pressure line?
This is what I'm using
Pegasus parts (www.pegasusautoracing.com) #3276-005 Male 16 x 1.5mm Metric Concave Seat to -6AN Male, Steel. Of course also a 16mm crush washer. I polished the edge of the pump provide a good seal. I've yet to turn the thing on so I can't say that it doesn't leak. Hopefully I'll know this weekend. If it works I'll add to the wiki.
 

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Dimitri,

Am converting a 1999 Toyota Tacoma. Installing late model MR-2 pump. Diagram shows Engine Control Module wired in. Is ECU necessary?

Your great work is very helpful. Thanks, loads!:)

Walt in Corvallis, Oregon
 

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The 2001-2005 MR2 PS pumps have a sensor which detects loss of hydraulic pressure, and goes into the ECU, and ultimately to a red light on the dash...

I am also converting a Toyota ('01 RAV4) so hopefully I can use the VSS signal (to de-sensitize the steering at high speeds) and also will hook up the P/S pressure sensor into the stock ECU.
 

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Thanks for the information on the role of the Engine Control Module (ECM) in warning of low power steering fluid pressure. There are two connections between the ECM and the Power Steering ECU, shown on the Toyota Spider MR-2 wiring diagram. One is labeled "EFI" and is on pin B6. The other is labeled "IDUP" and is on pin B1. Do you know which provides the low pressure warning and what is the function of the other? It would also be interesting to know the function labeled "WL" that is on pin C4.
 
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