RX 450h Power Steering Failure

[WXL]

I have an RX 450h SE-L from 2010.  It's in good condition.  But when I (occasionally) exceed 72mph (whether or not the cruise control is on) the power steering often (but not always) fails.  As soon as I stop, turn the power off then on again, the power steering is fine.  It works perfectly at lower speeds.  I can't see this being a Lexus safety feature (!).  Lexus say they can't detect the fault unless it's a "live" fault.  But I can't keep it as a "live" fault unless I drive with no power steering (which is like driving an old BL Land Crab...).  Any similar experiences / suggestions / thoughts from the Hive Mind?

[Herbie]

12 minutes ago, WXL said:

Lexus say they can't detect the fault unless it's a "live" fault. 

Is that what they told you on the phone or have you actually had it in the workshop for diagnostics?

What I'm getting at is, are there any fault codes stored that would give us a clue?

I've been in the electrical/electronic maintenance field all my working life and I do know what they mean - you can't find a fault if it isn't there at the time of testing.

You really need Techstream to diagnose something like this because so much can be gleaned from it without having to remove any parts as you'll see below:

[WXL]

Thanks for the reply, Herbie.  I've never had such an electronic car before (previous cars have been pretty mechanical...!).  So are you saying this:  if the power steering failed several times a couple of days ago, but it's OK now (because I turned the power off and on again and have only driven slowly since then) will there be a fault history (from a few days ago) that can be diagnosed when I take it back to the garage?  Or does the fault history disappear once the fault is no longer there?

[Herbie]

3 minutes ago, WXL said:

Or does the fault history disappear once the fault is no longer there?

No, there will (should) be a fault history. Any OBD2 scanner will show some diagnostic trouble codes but Techstream is the diagnostic software used by Lexus techs in the dealer workshops and can provide infinitely more info.

[WXL]

Thank you. I'll mention this.  I guess that may also reveal another message that reads: "Check Active Stabiliser Suspension System".  Have a good weekend.

[Herbie]

If you have a laptop and want to do some diagnostics yourself You'll need a miniVCI cable like this one.

These cables invariably come with a pirate copy of Techstream but, of course, I can't condone using it; that would be a matter for your own conscience. The correct way would be to legally and freely download Techstream from here https://www.lexus-tech.eu/ and then pay for a block of time to use it, but you'll need that VCI cable anyway, whichever you choose to use.

Here's just some of the Diagnostic Trouble Codes associated with power steering:

[Martin1977]

Hi,

Is yor problem solved whit steering and active stabilizers? I have exact same problem whit my 2010rx450h. Always it happens 103km/h or higher. I visited 2-3 times Lexus dealer for service, but nothing: evrithing is working fine untill next time. Trouble codes showing always shows that DC/DC converter fail, but they tested whit used DC/DC converter and still same...