Toyota MR2 Power Steering System

Everyone has wondered how to control the MR2 Power steering pump so that it is not a noisy power hog because it’s always on full throttle.  Designing some sort of motor controller or using a small off-the-shelf controller would not work for me.  One, I’m not that great of a designer of controllers (I’ll leave this up to Otmar). Second, a small off-the-shelf controller would not work on high voltage systems.  Plus, I would have to program some type of Micro or Basic Stamp to get all the functions I want.
So I decided to get the original motor controller from a MR2 at the junk yard and try to wire it up.  Well, it works better than I anticipated.  One of the modes of the MR2 controller is to slow the hydraulic pump to a stop when there is no movement of the steering wheel or vehicle road speed: saves power!  I have also wired it to enable itself when the Zilla Contactor is engaged.  I'm using the original steering wheel sensor from the MR2, so it senses how much steering I'm applying.  It is also getting road speed info from the cruise control speed sensor to limit over-steer at high road speeds.  It uses the sensors in the pump to tell you when the brushes are worn or overheated.

What you need:
The P.S. schematics provided are from a ’94 and ‘95 MR2, so try and get all the parts from a Toyota close as possible to these years.  There are a couple different versions of the schematics here, so use the one that best suits your needs.

1. Hydraulic Pump from an MR2
2. P.S. ECU (not the main engine ECU)
3. P.S. Driver (Main Relay is externally attached)
4. P.S. Sensor (inside the switch cluster from the steering column)
5. Wiring harnesses for all above
6. Micro-sized relay with N.C. contacts
7. 1K Ohm resister
8. Various multicolored automotive wire and loom to rebuild the Harness.
9. 80 Amp Fuse

The Hook up:
With the schematics provided you have to build a new wiring harness from the OEM harness cut out of the MR2.   It’s a lot of work so get busy…

1. I used the original cruise control speed sensor for my ’85 S10 to drive the ECU and it has worked with good results.  Your results or pulse rates may vary.
2. The ICT (PSCT) is a control wire for the main engine ECU to enable the P.S. when the engine is running.  The P.S. ECU is disabled when this wire is brought low (grounded).  So I used a micro-sized relay and a 1K Ohm resister to keep this wire low until the main contactor is engaged.  I hooked the small relay in parallel with main contactor.  My Zilla has no problem with this...
3. My Hydraulic pump was from a slightly different year so it had only 3 sensor wires.  After some testing I realized that it was missing the V-L or Violet/Light Stripe wire.  Look at the schematic and you will see how easy this was fixed.
4. The TC (CHK) and IDUP wires I did not hook up; apparently they are not needed.

1. Put a switch in your dash to disable the P.S. ECU via the ICT (PSCT) control wire.  I call this Stealth Mode…
2. I used a self-resetting 80 amp breaker instead of a fuse.  Your preference…

Circuit Diagram 1

Circuit Diagram 2

Connector Layout

System Outline

Operation Diagram 1

Operation Diagram 2

Courtesy of John Grigg