I’ll double check whether voltage drops to 0 with the key in off position or not. Aux battery was dead when I got the car, so I had to put a jump box to start it. It runs and drives fine except for the no power steering. I found some instructions on how to diagnose ecu and converter. There’s no power (0V) on the white wire mentioned below. However I didn’t have time to jump yellow/black wire to verify if I can get 42V on the white wire manually which I’m willing to try sometime this weekend.

• Check for 42 volts on the White wire at the Power Steering ECU connector (P47 – 1).
  • If there is voltage, the converter is good. Suspect Power Steering ECU.
  • If there is no voltage, disconnect Power Steering ECU connector, start the car, and apply 12V to Yellow/Black wire (P41 – 11). This is 12 volts coming from the Power Steering ECU to tell the Power Steering Converter to output the 42 volts. 42V should now appear at the White wire (P47 – 1).
    • If there is no voltage, verify that between the Red wire and the Blue wire at the Power Steering Converter there is at least 288V when the ready light is on. Check fuse if there is no voltage. Fuse is replaced together with the Main Relay.
    • If there is voltage, check Power Steering ECU power and grounds. If OK, replace Power Steering ECU.

 

https://techinfo.toyota.com/techInfo...ocs/rx400h.pdf

 

Nice IMSQ!

Hybrid Battery voltage specs from IMSQ's link to document here.

 

Ok, so I bypassed the steering control module by sending 12v back directly to the converter through the black and yellow wire and voilà- white wire now reads 42V. After all dealer misdiagnosed the converter. For those of you who might be suffering from the same issue don’t forget to check mpx-b1 7.5 Amp fuse under the hood, may be as simple as that if you’re lucky. I took apart my control module and it does have a burnt smell, unfortunately I can’t see what’s wrong with it cause I would need to unsolder lotta pins to get to its heart. I just ordered a replacement control module(ecu) from eBay and about to order replacement shocks/controls arms from rock auto and hopefully RX will be back on the road by memorial weekend.

 

Are you friggin' kidding me???

If your Power Steering ECU(control module) smells burnt I can promise it's junk, no questions asked!

You Rock man for diggin in this deep.
Plz keep us posted and let us know what you find and share more pics if you like.

 

Power steering control module arrived today. It doesn’t seem to make any difference. Plugged it in, cleared all the codes and… still no power steering, c1568 is back too. I double/triple checked the eps ddc , mpx-b1 and all other fuses again - everything’s sound there. I don’t get it. There’s always a chance that this control module is also bad. Either jumping the black/yellow wire and reading white wire voltage was inconclusive or there’s an intermittent problem with the dc converter. Reading 30v instead of 42v the very first time was kinda strange too. I found some local junkyards that seem to have dc converters available, so I’ll give it another shot. Are there any other modules I could be missing?

ps: dc converter reads 0V with key on or off until you actually start the car( ready mode), only then it reads 300v

 

That sounds ok I think based on the testing steps you posted above.

I have a lot diagnostic info concerning this system, too much to put here.
Pm me if ya want and I'll get for you when I can.

Others may have ideas too.

 

Ok everyone thanks for chiming in! Car is finally fixed. I can’t believe that $100 part totaled this vehicle. My original diagnosis was right I just happened to buy defective power steering control module. Hope this helps someone to diagnose their no power steering conditions in the future:

1. Start by checking mpx-b17.5 Amp fuse first (the easiest you can do)
2. If fuse is ok - check for 42V on the white wire at the power steering ecu connector P47-1
3. If there’s voltage- dc converter is doing its job, suspect power steering ecu( car should be running/ in ready mode while testing)
4. If there’s no voltage , turn off the car, disconnect P47-1 plug, start the car and apply 12V to black/yellow wire ( ideally through the 5 amp fuse so you don’t fry your dc converter). 42 V should now appear at the white wire( proving that dc converter is good)

*Measure continuity between 2 power pins ( see pic below). If there’s a short - replace your power steering ecu( that’s how I diagnosed mine and the one that I bought from eBay) Good module should read 500-600ish Ohm, bad module - 0.0x


5. If there’s still no voltage- turn the car off, disconnect the orange dc converter plug, set you multimeter leads and start the car to see if there’s at least 288V present between red and blue wire. Be extra careful doing this step as there’s a high voltage( 300v) that can be very lethal!!!
6. Still no voltage? Check the main DDC fuse ( fuses) that’s located inside the hybrid battery. Fuse is a part of the relay module that needs to be replaced as a whole unit( however some people managed to only replace/retrofit the fuse itself)

Good power steering module

Bad power steering module

 

Hate to bring this thread back to life but It’s been a few months and I still can’t get a state inspection done on my RX. Right after I replaced power steering ecu I started driving it and noticed that steering wheel is binding at low speeds , and if you keep fighting it it’ll just turn off power steering completely and ps light will come on ( c1568 code). I then spent a few days reading forums where people suggest replacing rack and pinion assembly as they tend to go bad especially after the accident. So I went ahead and ordered a replacement rack from the local junk yard, installed it, aligned the car, calibrated sas and torque sensor - same problem. Found some play in the intermediate steering shaft right under the dash, replaced that as well with a brand new oem part - didn’t help. Today I picked up a brand new oem rack and pinion assembly from the dealer( thinking that I might actually have a defective rack that I got from the junk yard) and after replacing it and recalibrating steering wheel angle sensor and torque sensor my problem didn’t go away. At this point, $1200 and 3 months later I’m kinda desperate and don’t really know what to do next. I don’t even know if my problem is mechanical or electrical at this point. Any input is appreciated

 

Hi angineer, a couple questions for you to rule out the easy stuff.

1) Where is the power steering ecu located? if under the dash make sure the ecu chassis is bolted down tight as I'm sure it is using a frame ground and this also applies to the DC/DC converter so make sure that is bolted tight too, clean connection.

2) Will the PS light and codes stay away if you gently steer without making it grunt at slow speeds? Another words will it function properly as long as you don't demand too much from the steering?

Some simple things that are very important, a good ground will be necessary if the servo in the steering rack is using high amps so someone can try to add an extra frame ground somewhere to beef up the frame ground and see if it helps or not. A jumper cable or something can maybe work to clamp onto the frame and negetave battery terminal and while not driving turn the wheel and see if improvement. This will rule out a frame ground issue and have somewhere to start.

 

ECU module is under the hood by the driver side wiper. Problem is somewhat intermittent and is mostly occurred when parking/turning in the tight spot while going really slow or stationary. If I don’t fight it and turn the wheel in the opposite direction for a sec and try again it gets smooth again. PS light goes off after turning the car off and back on and everything goes back to normal until it starts binding again. Obviously there’s more resistance when car is stationary when going really slow so either electronics detect some spike in current/voltage and everything cuts off or there’s a mechanical problem that prevents steering wheel from turning smoothly (but then why c1568 again?)

 

Here is what we know so far.
Your old one was shorted out and because of this was pulling high current and throwing a code.
Now you only get the code when turning while driving slow and as you said it requires much more power(V x I) to turn the wheels when car is idle or going slow.

If it was my car I would make sure the grounds are good and then montior the input voltage going into the power steering ecu from the DC/DC converter and see if the voltage drops significantly when under strain turning the wheels at idle and not moving. If the voltage drops the current will increase in direct proportion. so I would rule this out first(power delivery issue to the PS Ecu when under strain).

PS- if you do see a voltage drop at the PS Ecu when turning the wheel under strain(car not moving) I would do the same test at the DC to DC converter on both the hybrid battery input voltage wires and the output wires going to the PS Ecu. The dealer said they replaced the fuse that feeds the DC/DC converter(expensive part) but what if they put the customer's old bad fuse back in if the repair quote wasn't approved and the fuse is burnt or cracked and only works when there is a low power requirement such as when not straining it. hmmm

 

Ok so I went ahead and ran some tests on both ends of the dc converter and power steering ecu. Voltage on Power steering ecu ( coming from dc converter) and dc converter output drops to 12-20V when I start turning the wheel(only when binding, which I believe is caused by motor shutting off) . Voltage coming from hybrid battery to dc converter remains the same and doesn’t drop regardless of anything. I checked both dc converter and power steering ecu grounds and they’re tight and clean. Now, do you think dc converter is at at fault at this point or there’s a possibility that power steering module may have an internal short (increasing internal resistance makes the voltage to drop under certain conditions) ?

 

I think you just diagnosed it so good job on that!
No voltage drop on the hybrid battery high voltage into the DC/DC converter means the special fuse was probably replaced and seems legit aka no voltage drop there.

*note- for anyone following in the future the DC/DC converter is also known as the "Power Steering Converter" as seen in the drawing below, yeah it's confusing but same part so maybe they couldn't agree on what to call it cuz it's the same item with 2 different names depending on the schematic or drawing or info in the manual. lol

>> Ok this is huge- When the voltage drops from 48V to 12V, this means the current demanded by the PS Ecu will be quadrupled aka 4x current draw.
Hopefully the Hybrid Ecu saved your new rack by cutting the PS Ecu from straining so hard.

Inside the rack is what looks like to me an asynchronous servo motor.
It appears the voltage drop when under strain is sending the PS Ecu into current overload.

At this point it can be iether the PS Ecu or the DC/DC converter and hopefully that narrows it down and not something else but my guess it's one of those 2 things or something in the wiring between point A and B.
If it was a false alarm due to a damaged Hybrid Ecu we wouldn't see a voltage drop but we are seeing exactly what we expect- steering under strain and Hybrid Ecu cuts the PS Ecu to save it hopefully.

I grabbed this from my post above to put it in the context here, notice the U,V, W power wires going to the steering rack's motor from the PS Converter(DC/DC converter)
Power Steering Ecu(PS Ecu).

Add- and you can see where the Power Steering Ecu gets it 48V voltage power supply from the Power Steering Converter(DC/DC converter), for anyone following along.

 

Margate330, as always thanks for assisting and guiding me. I was impatient to wait until replacement modules come( ordered them 2 hours ago from eBay again) and then I remembered that I have Ebike with a 48V battery pack in it so I decided to jump my power steering ecu straight from the Ebike battery leaving dc converter unplugged and voila , no more binding steering wheel is smooth as butter.