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No return to center in steering

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Frontporch, Jul 17, 2022.

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  1. Frontporch

    Frontporch Member

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    No significant improvement with regreasing. I think I am going to live with less than perfect steering and wait to see if it gets tighter and then dig in with a replacement.

    Its definitely not perfect, but something I can live with. The biggest issue is that it does not return to straight on the highway in either direction (left or right turn). My brain has been trained to let go of the steering to compensate, but for the prius I need to bring it back to center.

    My options at this point are
    1. ignore it because its really not that bad and its winter time and I have limited ability and may make things worse
    2. investigate how to set a prius steering center point
    3. replace the rack
    4. get an alignment

    #4 won't help this issue.. that's just my gut feel
    #1 will let me see if I can live with what I have
    #3 is something for the springtime

    #2. I briefly glanced at that and it appears I need techstream or something similar. That would be a good task for me to work on during the colder weather.

    One final thought. I did have the car on jackstands, motor off, and turning the steering wheel lock to lock was NOT effortless with tires off. I wonder if this should be easy (fingertip) or am I working against the electric motor that assists. I didn't want to dig deep enough to start disconnecting the steering column from the rack, but just wondered if there is a pretty high chance that most of the resistance is from the rack.
     
    #21 Frontporch, Nov 21, 2022
  2. ChapmanF

    ChapmanF Senior Member

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    Steering gears don't really have "center points" to set in that sense. I mean, obviously, there's a point equidistant from both ends of the rack, and you kind of want that to be when the car goes straight (tie rod adjustments dial that in).

    But it's not as if there's any kind of spring in there trying to return things to a "center" point, and it's not as if the electric steering assist tries to return it back there for you. The return to center force just comes from the weight of the car and road forces acting on the alignment of the front wheels.

    There is a steering angle sensor behind the steering wheel, which the skid ECU can use to notice when you're skidding (if the steering angle doesn't agree with the way the car is going). It calibrates itself on each drive (when you're driving normally and going straight, the ECU looks at whatever number is coming from the angle sensor and says "we'll call that zero").

    In cars with parking assist, the angle sensor can also be used for that, and the parking ECU does have a "reset zero" function. If it is off, the parking assist and the guidelines shown in the backup camera may be off.
     
    #22 ChapmanF, Nov 21, 2022
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  3. Frontporch

    Frontporch Member

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    Right... no mechanical center point in the rack, just a "software" setting in (the steering column or a sensor thereabout) to what should be dead straight ahead. Looks like most common issue with that being "off" is that the vehicle assists differently when turning slightly left or right from center. If the amount of effort is different, the vehicle probably doesn't agree with where the "center" really is. not my issue.

    That makes sense. The vehicle itself should want to right itself if the alignment is good and there is no other factor like brakes dragging or uneven terrain or wind. Even under acceleration that probably should be a constant that everything goes back to straight ahead motion.

    If there is no drag from a sluggish or confused motor and the several bearings an u-joints on the column, then probably it is that rack. The struts are new...ball joints and steering linkages I assume aren't giving much resistance.

    I like to repair things based on some diagnosis but I have the best results with replacing well known failures. Seems these racks can fail, but it doesn't appear to be that common. A guy on youtube had 10 2-3 minute videos on taking the rack out. His had play by the pinion shaft on the top of the rack and it caused all kinds of sensor issues with alarms going off... I am nowhere near that. LOL.
     
    #23 Frontporch, Nov 21, 2022
  4. ChapmanF

    ChapmanF Senior Member

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    I don't think that's the case. While there is a steering angle sensor (it lives right where the spiral cable is), the ECUs in the car that care about it are the skid ECU and (if you have it) the parking assist ECU.

    Surprising as it may seem, the power steering ECU doesn't give a hoot about the steering wheel angle sensor. That isn't even an item in the power steering data list.

    The steering ECU gets all it needs from the steering column torque sensor (which lives right near the electric assist motor). That only measures how hard you are turning the wheel, not which way the wheel is pointing. When it senses you giving torque to the left, the ECU gives more torque to the left. When you give torque to the right, it gives more torque to the right. When you're not giving torque, it doesn't either.

    The steering ECU also gets the vehicle speed signal; it dials back the amount of assist it gives you, as the car goes faster.

    There is a procedure for setting the zero point of the torque sensor. And if that is off, then yes, you'll have unbalanced assist to the left and the right.

    There are a couple places in problem-symptoms tables where the repair manual says "steering center point (zero point)" as a possible suspect for "steering effort differs between right and left", but that confusion might have crept in during translation. It's talking about the torque sensor. The reading should be zero whenever the torque is zero, and the torque is zero any time the wheel isn't turning, whether centered or not, as long as the reason it's not turning isn't because you're holding it there.

    In the torque zero point setting procedure, they have you point the wheel straight ahead and keep your hands off it, because straight ahead is an easy standard situation. But you could still learn the zero torque value with the wheel pointed another way, as long as there was no torque on it.
     
    #24 ChapmanF, Nov 21, 2022
    Last edited: Nov 21, 2022
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  5. Frontporch

    Frontporch Member

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    Oh no... which wheel are you referring to? there are five... not including the spare tire.

    Boy these cars are necessarily complex and there is a reason why I didn't become an electrical engineer... actually lots of them.

    I will need to ponder this for a while...
     
    #25 Frontporch, Nov 21, 2022
  6. jdenenberg

    jdenenberg EE Professor

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    I believe that it is the camber of the front wheels that provides the "return to center" torque for the steering.

    JeffD
     
    #26 jdenenberg, Nov 21, 2022
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  7. ChapmanF

    ChapmanF Senior Member

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    The steering torque is zero whenever the steering wheel isn't turning, as long as the reason it isn't turning does not involve being held in position.
     
    #27 ChapmanF, Nov 21, 2022
  8. Frontporch

    Frontporch Member

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    I greased the steering rack several times now and it seems to be marginally better but still not right. I came across an EBay listing for a used rack and am going to jump on that this week and install it when I can.
     
    #28 Frontporch, Dec 12, 2022
  9. Frontporch

    Frontporch Member

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    quick update. the new (used) rack is installed. It was smoother and easier to turn than the one that was in the car. I could turn the input shaft with my fingers on the new rack to make it move before it was installed... the existing rack was not the same.

    Sadly after installing and getting a 4 wheel alignment, the centering issue is still there. Since I was learning to live with it before I replaced the rack, I am going to stop trying to fix that.
     
    #29 Frontporch, Jan 3, 2023
  10. dolj

    dolj Senior Member

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    So, did the alignment shop mention anything about the tie-rods being at the max point, so no further adjustment can be made? If not, it sounds like maybe something is bent up elsewhere and some dimension is out of the spec.
     
    #30 dolj, Jan 3, 2023
  11. ChapmanF

    ChapmanF Senior Member

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    "My steering wheel isn't exactly centered when the car is going straight" and "after turning, the steering doesn't tend to return by itself toward going straight" are different issues. The first one can be amenable to tie-rod adjustments.
     
    #31 ChapmanF, Jan 3, 2023
  12. Frontporch

    Frontporch Member

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    The shop had the Prius for about 40 minutes. It was on the rack with some calibration devices on all four rims. It was taken down and driven. On return it was back on the rack. At this point I think the front wheels were suspended freely and adjustments were made to then tie rods. The car was put down and driven again. I paid and got a printout. Nothing was said about it being out of spec
    The way the car drives I can go freeway speeds and turn the wheel either to the left or right and it can hold a gradual curve by itself. No shaking. No pulling. I am guessing maybe 3-5 degrees
     
    #32 Frontporch, Jan 3, 2023
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