Inconsistent power steering feedback

[Linas.P]

It has been a while, but I have come up with interesting fault (from boredom with otherwise reliable car)... 

This "issue" has been propagating itself since I have bough a car. I would say generally IS250 steering is quite light, which I don't exactly like but it is nothing wrong with that. On my particular car I had period where steering would become heavier which I generally prefer. To some extent it sometimes reflects tyres and tyre pressure e.g. higher pressure would make steering feel "lighter", but in my car there was certainly something else - even on the same tyres/pressures it would be just heavier for a period of time e.g. like 6 weeks and then again it would be normal for couple of months... never really bothered me so never looked to fixing it. 

However, yesterday on my way to work steering become so light that for a moment I thought steering wheels has detached (scared me)! The feeling was literally like of cheap gaming wheel - just a plastic wheel on shaft - no feedback. Parked the car at work during the day and on the way home steering was nearly back to normal... and today totally normal.

No error codes, lights on dash, sounds, smells etc....

I assume that if electric power steering would be on it's way out, it would simply become stiffer and stiffer until it would die. Now it goes from light to stiffer for prolonged period of times... and as of yesterday it apparently goes "super-light" as well. I am just wondering what could be causing such issue?! Is there something like angle/speed sensor which controls power steering which could be in some way faulty to give such sporadic behaviour? Really struggling to think of anything.. 

 

[Texas]

Is there anything you can interrogate via Techstream, like a PS Ecu or view the parameters of the steering geometry?

[Linas.P]

Standard OBD2 scanner shows no errors. Currently, I don't have access to Techstream.

Looking through repair manual it seems there are all the sensors I guessed there are:

• Speed sensor
• Angle sensor
• Skid control ECU
• Power steering ECU
• Combination meter
• Torque sensor (Built into steering gear assembly)

The manual only mentions issues of heavy steering, but nothing regarding light. I guess following issue description would be closest to what I have: "While driving, steering effort does not change in accordance with vehicle speed or the steering wheel does not return properly."

Repair manual gives procedure for re-calibration, but it doesn't seems to be very straightforward:

GSIC - Global Service Information Center.pdf

I wonder if by "intelligent tester" and "DLC3" - they mean "Techstream" and "OBD2"

[johnatg]

Can't really offer any suggestions about the problem, but the Intelligent Tester is a bit of hand-held kit which is used for a whole lot of service procedures. It's not Techstream, and Techstream can;t be used for the things the Intelligent Tester can do. They come up for sale sometimes - they cost about £200. I have considered buying one, but you don't really need it for most diy service things. But Lexus do specify that you need it, for example, to bleed the brakes and change brake fluid - but I think I have done those things successfully without the tester.Maybe I haven't cleared fluid from some of the darkest recesses of the system or something. And there's a host of other procedures in the manual which start off by saying 'Connect the Intelligent Tester.....'.  I think it puts the ecu etc into some sort of service mode to override some normal operations or open up access to things like voltages within the system.

It is plugged in to DLC3 - that is the OBD11 port/connector.

[Linas.P]

Ok, thanks for replies - seems to be dealer type of service then. Perhaps I can asks them just to plug-it during next service as a freebee and see what they say. I am under impression that if any of the sensors have gone bad it would be rather expensive job requiring power steering motor and gear to come off - not exactly economical considering mileage and age. I guess this will the main the mystery and luckily it is back to normal now..