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Ls430 Power Steering Upgrade (Ecu)


mikelang19
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Hi. Thanks for looking at this question regarding a possible power steering ECU upgrade. Some background:

I purchased a 2003 LS430 last Oct (80k miles) with standard suspension. I have since upgraded the springs, struts and rear sway bar using OEM Euro/sport parts. It handles much better now, but the steering seems a bit over-boosted. I read that the power steering ECU for the Euro/sport susupension is different than the ECU for the standard suspension (a software remap?). That seems to be confirmed by the fact there are two different OEM part #s for the ECU (one original and one sport?). Here are the part numbers: 89650-50130 and 89650-50120.

The local, non-dealer repair shop that intalled the springs/struts/sway bar took apart the passenger side dash trying to find the power steering ECU, but no luck. Since then, I had a Lexus dealer tell me there is only one power steering ECU for all suspensions on 2003 LS430s. Can you confirm whether there were two different ECUs offered, and, if so, where the power steering ECU is located? (it's not behind the glove box, as part diagrams indicate.)

Any help/advice would be greatly appreciated.

Thanks...Mike Lang

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I recently read an article where some one had researched this on a LS400 and had fitted a potentiometer (think volume control on a radio) in series with the rack solenoid and could by adjusting this control alter the feel of the power steering but would you want to do this on a 430 is the question?

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I recently read an article where some one had researched this on a LS400 and had fitted a potentiometer (think volume control on a radio) in series with the rack solenoid and could by adjusting this control alter the feel of the power steering but would you want to do this on a 430 is the question?

Possibly but I have some doubts about this. Since the concept is speed variable steering there needs to be a speed input. This is likely a digital input from the engine ECU. Probably a pulse train proportional to the odometer. The output then would be to drive a solenoid value in the rack and pinion to vary the hydraulic power assist. Given the relatively low impedance of a solenoid valve this output is probably fairly beefy from a current drive perspective hence it rules out a potentiometer trim of the output. It is probably a pulsed to ground switch where the duty cycle of the switching determines how open the valve is (the IACV is controlled in a similar manner).

So if you desire stiffer steering and the speed sensitive nature of the design is to back off the hydraulic assist with increasing speed then you just want more of that (more backing off that is). That can be solved by modifying the solenoid drive circuit to have it assist less or "trick" the ecu to see a faster pulse train so it thinks the car is moving faster than it is.

Either of these approaches would take some work to design a black box to insert and modify the behavior. Of the course the easiest would be one or two lines of software code changes in the ECU. Unfortunately I doubt Lexus releases the source code for this so people can modify it!!

A last solution might be to modify the hydraulic assist mechanicals. If there is a solenoid valve that opens and closes to vary assist maybe by making it permanent partially open or limiting it so it never is fully open you can peg the upper limit of assist. Maybe a hydraulic person can chime in on this.

It’s an interesting concept but probably a lot more work than it is worth. Lexus never said it was trying to be like BMW. If you want that feel you bought the wrong car. This is a big lumbering comfy couch. Accept it for what it is.

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  • 1 month later...

Thanks to all who replied. I'll probably just live with the over-boosted steering, but I still wonder why there would be two power steering ECUs part #s if one wasn't for the sport/Euro factory package. I might just spring for it if it's only $100 or so.

Thanks again, Mike

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