Good job, sounds like the DC/DC converter is dying and dropping ot when it's under strain from your description.
Bypassing it by voltage injection is a legit way to bypass it for testing as you just proved.

How is the parts availability and price on the replacement units?

*note for anyone following along, plz use angineer's steps above to check for a short circuit in the Power Steering Ecu FIRST- before applying voltage injection with a battery pack or unregulated power supply because battery fire or damage to the car or self can occur.

 

Wow, that's an impressive stream guys (if you are still reading this). My 2006 RX400H had curb-clash trauma and resulting PS loss. Dealer couldn't solve it, and the local auto electric shop (a couple of honest old-timers) got as far as 'no 12V coming out of the ECU. I'll check the easy to check fuses, and am awaiting my salvage yard ecu for replacement installation. I'll have it checked by the old timers before installation.....
My 400 is just so ideal: still handsome and running smooth (until this) and doubling as the hauler for my carpentry tools, lumber on top and general dirty work on one hand, and then cleaned up and ready to go out on date night. Hope we can save him!

 

Hi friend, as seen above there are three suspect components, plus some other fuses.

1) DCC fuse: this is a special fuse located at the Hybrid battery. It's only job is a fuse for the DC/DC converter

2: DC/DC converter aka power steering converter. This is a step down power supply as seen above. It takes the high volts from the hybrid battery and steps it down to 48 volts to run the power steering ECU

3: Power steering ECU: this piece takes the 48 volts supplied from DC/DC converter and turns the wheels. Wheels are turned electrically by an electric motor.

Check out Angineers post above, he gives a check list of what he found and some simple tests. Beware of high volts.

Wiring is also above.
​​​​​​
PS- on Lexus schematics a wire marked with "L" is always a blue wire.

PS- orange plug means beware, high voltage

 

Thank you Margate for the quick and efficient response. Yes I'd seen and admired Angineer's list and work. Even thought the result of all that seemed to be a less than perfect fix, it is an excellent education on the components and how they work (and possibly fail).

In my case, the dealership DID change out the PS ECU, and when the code didn't clear they moved on to replacing the DC/DC converter. When that too didn't work, they metaphorically threw up their hands and said " it must be in the wire harness somewhere and we don't recommend throwing THAT kind of money at it..." In the end (with them) they took back their parts and reinstalled the original ECU and converter and charged me pennies on the dollar for the labor, with the problem remaining. Meanwhile, I've driven the car for more than a month like this.

My last efforts before I throw in the towel are to get a 'new' salvage PS ECU (on it's way now), pretest it before swapping it out. But the other thing I want to do is check the two fuses on the underside of the relay boxes that sit between the center hybrid battery pack and the passenger side one. A You Tube clip showed a fellow who found those bad and replaced them, AFTER a new ECU and converter didn't work. And the fuses solved the problem, even before the ECU was recalibrated by the dealer later. So that's my target for now.

 

Hi guys wonder if you could help have been on this car for week now with this thread. Got exactly the same issue and have followed the steps on here exactly the same happening checked the main ddc fuse (ok) also checked the 42v from white wire no voltage until I bypass it with the 12v battery In the p41-11 and then bang get 42v on white wire so converter ok have also changed that as well. Have changed the ecu twice and still getting the p1568 code. I have plugged in my computer and got real time data and the DRDD data shows only 0.2 v when it should be reading 12v to get the converter started. The question I have is why is the car not sending the 12v down the DRDD lead to signal the converter to kick in is it the ECU that signals this??? Any help would be greatly appreciated as am at a cross roads

 

Hi,

Just so we don't take away from this thread, I made a new thread just for the DC/DC converter troubleshooting, link: https://www.clublexus.com/forums/hyb...converter.html

 

Red and yellow wires and red and white wires are the power steering converter malfunction signal wires

 

Hi - did you have any luck in figuring out the PS? I have a 2006 400h and having the same issues and narrowing down potential issues.