1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Headlight leveling sensor DIY repairs - have they held up?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by ejensen, Jun 21, 2012.

  1. ejensen

    ejensen Junior Member

    Joined:
    Jan 31, 2004
    8
    4
    0
    Location:
    Philadelphia area
    I've seen several threads where people posted about repairing their own headlight leveling sensors - cleaning out the corrosion, reassembling, and reinstalling.

    I just got the warning symbol that mine has failed, so I'm thinking of trying the repair myself, too. But I thought I'd ask here: how have people's repairs held up? Have you had to go back and eventually replace it? Is there anything you wish you had done differently when you repaired it?

    On a related note, I see that the Toyota Service Bulletin for this problem instructs the mechanic to "Perform the Headlight Leveling ECU Initialization procedure using the SST" and then to "Perform the Headlight Aim Only procedure." This doesn't seem like something an individual can do without specialized equipment / knowledge. Is there a way to do it? Is it unnecessary?

    Thanks in advance,

    Eric

    P.S. Here's the TSB: http://ww2.justanswer.com/uploads/PENTICO/2009-05-01_195955_prius.pdf
     
  2. jadziasman

    jadziasman Prius owner emeritus

    Joined:
    Jan 17, 2011
    1,355
    486
    0
    Location:
    District 6
    Vehicle:
    Other Non-Hybrid
    Model:
    N/A
    Life is like a box of choc-o-lates. You never know what you're gonna get.

    And it's the same for that dreadful headlight leveling sensor!

    I was able to repair it on my 05 and it has been functioning without any issues for the past month.

    I did not need to do any initialization procedures or any other aiming. Once the sensor was functioning again, it leveled the headlights properly.

    Taking the sensor off is easy. Make sure the car is off with the smart key system disabled and you can take the connector off without disconnecting the 12V battery, which they seem to want you to for every repair except changing wiper blades. Remove four fasteners and it's off the car.

    The sensor repair can be easy, difficult, or impossible.

    Sometimes the guts inside the sensor housing are completely FUBAR, which forces you to find a used one or shell out $$$$$$$$$$ for a $$ part.

    In addition to failure within the sensor itself, one of the three blades in the sensor connector snapped off when I removed the harness and the blade got stuck in the harness side. I was not able to extract it so I had to make a work around so that the connector would still function.

    My latest brillant idea was to completely surround the sensor with duct tape to prevent water/dirt/salt getting into the sensor itself and to surround most of the connector as well. I hope this will work. I purchased the thickest duct tape I could find and created a nice enclosure. So far so good.
     
  3. 8AA

    8AA Active Member

    Joined:
    Feb 29, 2004
    550
    62
    0
    Location:
    Maryland
    Vehicle:
    2004 Prius
    I repaired mine and it lasted for about a year before failing again.
     
  4. derekc

    derekc Junior Member

    Joined:
    Jun 5, 2007
    40
    10
    0
    Question guys, Do the headlights go up and down for few sec when you first turn on the engine and the lights?
    In my case, I just drove my wife 2007 prius and noticed passenger side headlight is beaming way up than the driver side one. I thought I screwed up the alignment when installing two new HID bulbs a few months ago so I took them out and found no problem. Now, after much research, I learned there is a leveling sensor in the back next to the left wheel. However, the car gives no warning light on the dash at all. When I jumped on the rear bumper, I didn't see the headlights moving up and down at all. So, the leveling sensor is bad? Or the ECU? Or the leveling motor(s)?
     
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,198
    6,461
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    No, the headlight aim will not routinely change as you turn on the lights.

    If one headlight is high (or low) compared to "normal", then it sounds like the problem is with the motor for that headlight.

    If the aim of both headlights are incorrect, then I would suggest the sensor as the most likely failed component.

    Could it be that your system has two problems?
     
  6. ejensen

    ejensen Junior Member

    Joined:
    Jan 31, 2004
    8
    4
    0
    Location:
    Philadelphia area
    A couple of thoughts. First, there's only a single leveling sensor, which provides feedback to adjust both headlights. So if you have one headlight pointing to a different level than the other one, it's not the leveling sensor.

    Second, it's not something that responds quickly - when the level of the car changes, it takes a few seconds for the level of the headlights to adjust. So if you literally "jumped on the rear bumper", you wouldn't see a change right away (unless your balance is very good and you stayed there for a little while and carefully watched the headlight level).

    Finally, the car might not report a problem with the leveling sensor even if it's not working, depending on the mode of failure. The car can detect when the wiring has failed (e.g. some of those contacts inside the sensor have rusted out) because the sensor is no longer providing the right resistance in that case. But what I found in mine is that it was pretty clear that the sensor hadn't really been adjusting the headlights for a while, because the lever arm wouldn't move at all. (There's a lever that is supposed to move when the back of the car moves; this lever then turns a variable resistor inside the leveling sensor, and the changed resistance sends a signal to change the level of the headlights. If the lever doesn't move, the headlights don't move - but the car won't report a fault if the internal contacts are still intact.)

    How do I know how long it takes for the headlights to adjust? Because I can now adjust them manually. I replaced my dead leveling sensor / lever arm with a $3 Radio Shack potentiometer wired into that circuit. It's in an Altoids tin with a knob attached, sitting in the storage bin under the floor of the back hatch. So I have a manual (rather than automatic) headlight leveling adjustment now... Not ideal, but it just didn't seem worth it to shell out the money to replace the sensor. I can post pictures / specs if anyone is interested.

    Eric
     
    SFO likes this.
  7. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,198
    6,461
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    Good idea, Eric. Please indicate the resistance spec for your variable resistor in case anyone else wants to follow suit.
     
  8. derekc

    derekc Junior Member

    Joined:
    Jun 5, 2007
    40
    10
    0
    I see. I have a lexus LS and when I turn on the lights, it goes up and down for a few sec (just to tell me leveling is working) Ok. Prius doesn't do that.
    So far, I have never caught the headlights moving up or down at all but now the passenger side light is a tiny bit higher (after I reinstalled the bulb maybe), normal? Or they are supposed to be dead level?
    I guess I can go under the car and see if I can move the lever to make sure it is not stuck and to see if the lights will move (giving it a few sec to response.)
    If still no problem found, I will just manually adjust the passenger side light to level it with the driver side. It is possible to do a minor physical adjustment on the motor itself, right? (My wife got into a minor front bumper accident crushing the foam piece inside and I replaced it.)

    Yes, it could be multiple problems. First, because of the minor accident, the headlight aiming simply needed an adjustment. Second, the leveling sensor might be just stuck/rusted but not giving error to the ECU.

    Hmmm, those level motors are moving some aiming or focus reflective device in front of the bulb but not moving the bulb. Interesting...
     
  9. derekc

    derekc Junior Member

    Joined:
    Jun 5, 2007
    40
    10
    0
    I just went under the car. The lever is tied to the frame and not moving unless the suspension has load. So, I can't tell if it is bad unless I remove it for inspection. Jesus Chris. This prius has not been a fun car.
     
  10. johnjamis

    johnjamis Junior Member

    Joined:
    Jul 4, 2009
    79
    13
    0
    Location:
    KY
    Vehicle:
    2012 Prius
    Model:
    Two


    Great idea, Eric. Since you have already built a working headlight level adjuster, I want to know exactly what components (Radio Shack part numbers) you used and how you hooked them up. Pictures would be helpful. Thanks for your efforts.

    I have also thought that a single resistor could be wired into the system in place of the leveling sensor to set the headlight level at a proper fixed position. What resistance would be correct and what would the circuit look like? John
     
  11. gwormser

    gwormser New Member

    Joined:
    Jan 13, 2013
    4
    0
    0
    Location:
    tampa fl
    Vehicle:
    2005 Prius
    Model:
    N/A
     
  12. gwormser

    gwormser New Member

    Joined:
    Jan 13, 2013
    4
    0
    0
    Location:
    tampa fl
    Vehicle:
    2005 Prius
    Model:
    N/A
    please indicate the value of the poy\t or the rs part number a pdf of your wiring or pic would be nice too
    great idea dude
     
  13. ejensen

    ejensen Junior Member

    Joined:
    Jan 31, 2004
    8
    4
    0
    Location:
    Philadelphia area
    Thanks for the reminder to follow up on this.

    The resistance from the original leveling sensor is about 3900 ohms across its full range of motion. But it was hard to find a 4K-ohm potentiometer, so I used a 5K-ohm one from Radio Shack instead:

    5K-Ohm Linear Taper Potentiometers : Potentiometers | RadioShack.com
    5K-Ohm Linear Taper Potentiometers

    Model: 271-1714 | Catalog #: 271-1714
    The car's circuit doesn't like having a full 5K of resistance across that connection (i.e. it will give the same "sensor failed" warning as it does if you have nothing connected) - but that just means you don't turn the knob through its full range of motion. Just use the first 3/4 or so of the range of travel of the potentiometer to get the full range of adjustment of the headlight level.
    The three wires from the original sensor just attach to the three connectors on the potentiometer. Map the middle wire from the sensor to the middle wire on the potentiometer and you're fine - swapping the outer two just affects which direction the headlights move (up vs. down) when you turn the knob in a given direction.

    I'll try to post some photos of my installation, but this is the essential info. Let me know if you have any questions.

    Eric
     
    SFO and johnjamis like this.
  14. ejensen

    ejensen Junior Member

    Joined:
    Jan 31, 2004
    8
    4
    0
    Location:
    Philadelphia area
    By the way, I also tried an "audio taper" (logarithmic change of resistance vs. linear change as you turn the knob) potentiometer in the circuit, and decided that a smooth adjustment seemed easier with the linear taper one I've linked above. But either would work.
     
  15. johnjamis

    johnjamis Junior Member

    Joined:
    Jul 4, 2009
    79
    13
    0
    Location:
    KY
    Vehicle:
    2012 Prius
    Model:
    Two
     
  16. johnjamis

    johnjamis Junior Member

    Joined:
    Jul 4, 2009
    79
    13
    0
    Location:
    KY
    Vehicle:
    2012 Prius
    Model:
    Two
    Great idea. Thanks for the details on how to to make a manual adjuster for the headlights. I am going to try this the next time my leveling sensor fails. John
     
  17. nh7o

    nh7o Off grid since 1980

    Joined:
    Dec 10, 2011
    1,686
    337
    0
    Location:
    Hawaii
    Vehicle:
    2009 Prius
    Model:
    II
    For those more daring, here is a way to have that potentiometer in the front of the car, say the glove box.

    Wire the potentiometer to the headlight beam level ECU, which is under the dash on the far passenger side. Cut wires 20 (yellow), 5 (blue), and 2 (purple) of connector H12, which is the 24 pin plug that goes to the ECU. Pins 20 and 2 go to the outer tabs of the pot, pin 5 goes to the wiper. Splice enough wire to the pot to place it where you like. I have not done this yet, it's just what the schematic indicates.

    You can just T-splice the above mentioned wires without cutting them, so as to leave the connections to the rear intact in case you ever wanted to reestablish the OEM sensor.
     
  18. ericbecky

    ericbecky Hybrid Battery Hero

    Joined:
    Mar 12, 2004
    4,365
    3,209
    1
    Location:
    Madison, Wisconsin
    Vehicle:
    2005 Prius
    Model:
    Two
    Just curious nh70, what value potentiometer would you use for the optional fix you mention?
     
  19. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,198
    6,461
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    Post #13 indicates that 3.9K is the total resistance required, so a 5K linear taper variable resistor with a 20K fixed resistor in parallel would yield 4K total resistance.
     
  20. ericbecky

    ericbecky Hybrid Battery Hero

    Joined:
    Mar 12, 2004
    4,365
    3,209
    1
    Location:
    Madison, Wisconsin
    Vehicle:
    2005 Prius
    Model:
    Two
    Yep. I saw that, I was just checking to see if for some reason there needed to be different values when tapping in at H12.
    Thanks!