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Thread: oil sensor wiring

  1. #1
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    oil sensor wiring

    I managed to break the wires off of my oil level sensor connector right at the connector, leaving me looking for ways to fix it. I was able to remove the terminals so I now have a way to repair it but then realized I have the old connector from my JDM engine, that was taken off when they installed it. Then I noticed it only has 2 wires, the yellow with red stripe and the center brown wire. The slot for the third wire, which is yellow with a green stripe on my harness, is plugged on the JDM connector so it was never there.

    Anyone know why that might be? Do I even need the 3rd wire? It will be easy enough to replace that missing connector with one from mine so I'm mostly just curious for curiosity's sake.

  2. #2
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    Re: oil sensor wiring

    I can tell you how the sensor works on my '92 but don't know if that's the same as your engine+engine computer+harness combo.

    The oil level sensor is a magnetized "donut" that floats up and down on a vertical shaft with the oil level. There are two "reed" switches mounted near the shaft ends, the top for the high level and the bottom for the low. [A reed switch is essentially two strips of metal, one of which will bend to touch the other when a nearby magnet pulls on it, making an electrical connection between the two strips.]

    Previa Engine Oil Sensor.jpg

    In the 1992, the schematic shows three electrical connections to the oil-level switch - the "high level" (yellow to OMS) and the "low level" (yellow/red stripe to OLS) - both of which connect to the engine computer, which places a couple volts on each (2.3V to 2.8V via a resistor to be precise) relative to ground (brown).

    Previa92 oil float.gif

    If neither switch is closed (because the float is not close to either), those voltages remain on OMS and OLS. If the float goes up or down and gets near a reed switch, it makes contact to ground and the computer sees zero volts on that connection.

    If the high-level switch is closed (zero volts on OMS), the computer will do nothing with the oil-reservoir pump; if the low-level switch is closed (zero volts on OLS) the pump will run. If neither the "high" level or the "low" connection is zero (i.e. the float is between them) the pump may run? (a supposition in the ToyotaNation post mentioned below). I suspect the pump stops either when the high-level switch closes, or after some pre-determined pumping time, so there's at least more oil added than would just raise the level above the low point.

    I looked it up and it appears that the sensor assembly is the same for all '91-97 models, so maybe a change was made at some point to only pump in "x" amount of oil if it's low. Maybe Toyota figured the "high" (yellow) switch wasn't necessary if the ECU waits for a "low" signal before pumping rather than "topping it up" if the "High" (full) isn't present. No way of knowing without ECU source code which may have changed between years.

    If you would like to go further down the rabbit hole on this (oh, you know you want to ), I refer you to a post on ToyotaNation by - as I recall - a literal Rocket Scientist.
    https://www.toyotanation.com/threads...rning.1132961/

    I know, I know, no answer to your question after all that. If it was me, I'd connect the yellow/green wire to the plugged connector spot and - as we all should do - check the oil level manually once in a while, especially if that reserve oil pump is always running at startup.

    Oh, yeah, and watch out for deer.
    Last edited by man_btc; 11-21-2023 at 01:09 AM. Reason: clarified if neither high or low connection
    "If you find yourself holding a sledgehammer or a crowbar, it's time for a break."

  3. #3
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    Re: oil sensor wiring

    Interesting. It does, maybe answer my question if Toyota deciding they didn't need the OMS is what happened. But if that is what happened, it must have only been in Japan (maybe post 97?) because my 97's harness has all 3 wires, as did the 93 connector I had on it. (it had no connector at all when I bought it, only 3 bare terminals). But it seems like a logical explanation.

    I suppose I could try it and see if it works without the 3rd wire, but the computer might not like that and the only thing to be gained is avoiding the 5 minute job of installing a 3rd wire and terminal in the JDM connector. So I think I'll stick with 3. I just need to find a better way to secure the harness so it doesn't hang up on tall grass or low brush again.

  4. #4
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    Re: oil sensor wiring

    For securing the wire coming out of the connector, on mine there's a bracket screwed to the lower-left, um - ear? - of the sensor. That bracket in turn has a protruding tab, onto which is snapped some plastic clamp-thingy that holds the wiring. If that bracket+tab is on yours, but missing the plastic piece, you could probably drill a hole in it where the plastic thingy should be and add a zip tie to hold the wiring. If no bracket, you could make something yourself out of a scrap metal piece and whatever (8mm?) bolt fits the bracket (you do have a shoebox with random pieces of scrap metal in it, don't you? ). Also a good idea -if it isn't already protected - is to generously wrap that part of the wiring in some good weather-resistant electrical tape - I'd recommend Scotch "Super 33" (good) or "Super 88" (beafier).

    Yup, always something.

    Not the best photo, sorry -

    Previa oli level bracket.jpg
    "If you find yourself holding a sledgehammer or a crowbar, it's time for a break."

  5. #5
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    Re: oil sensor wiring

    Yeah my bracket is completely gone, along with the head of the bolt that secures it. Having lots of fun now trying to drill it out. Drill battery on recharge, having barely made a dimple in it. After I run it down again I might be able to get an extractor in it

    I discovered the JDM sensor in the box of parts they took/ripped off of the JDM either during shipping or before installing it. Its broken but seems different than the 91-97 USA style although it does have 3 spade terminals. The bracket is gone from it too.

  6. #6
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    Re: oil sensor wiring

    Just for yucks I tried to run it with only the two wires hooked up, and I got the same frantic "oil level" blinking I had when I started this repair. Oh well, worth a try, but the pictures below will show why it was probably doomed from the start.

    I also found out it will be well nigh impossible to reuse the pins from my broken connector, they are just too small and fragile to open up to get the old wire ends out and new ones in. I scavenged through all of my Previa connectors and thought the injector connectors might have the same pins, but they don't. Plan B: jack up the old 93 in the yard and steal the connector off of it. That would have been Plan A, but I thought I took that connector off years ago.

    Here are pictures of what was apparently in my JDM engine when it shipped. It scarcely resembles the US sensors. I think something is maybe broken off, so it may or may not not show the full story.

    IMG_3917.jpg
    IMG_3918.jpg
    IMG_3919.jpg

  7. #7
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    Re: oil sensor wiring

    That sensor type seems to be used on many other Toyotas but not the Previa. To see it in action, you can go to this (leisurely-paced) YouTube video 5 minutes in.

    https://www.youtube.com/watch?v=NVs6eNXlaCM

    The quick functional difference is that the non-Previa float appears to move over a short distance to short two connections at the the top "full" position, disconnecting them when it's lower. As for the Previa-specific "donut" float layout, I suspect it has to do with (a) its location within the unusually-tilted engine which required a wider (mechanical) low-high float movement than the more common type, and/or (b) some requirement for more specific oil-level info required by the Previa's oil-refill reservoir-and-pump scheme.

    As extra info for future forum-explorers interested in the Previa oil level sensor, there also this earlier thread about how the oil level sensor functions and how to deal with it if it malfunctions.

    https://www.toyotavantech.com/forum/...sor-Best-Fixes
    "If you find yourself holding a sledgehammer or a crowbar, it's time for a break."

  8. #8
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    Re: oil sensor wiring

    Quote Originally Posted by man_btc View Post
    That sensor type seems to be used on many other Toyotas but not the Previa.
    It must have been used at least once, on my JDM. But maybe they just used it as an oil pan plug, like I'm doing with a broken one on my parts van. Who knows if it ever worked. I'm sure I could test it on my 2 wire setup but I'm not going to. I will let it hang around though, I may need it someday.

    It looks like it will be fun getting the connector off of my 93, I just looked underneath and the frame is very badly rusted. I may have to dig a trench instead of jacking it up, but the ground is already freezing at night. First thing will be to pump up the tires, then I might be able to slither under far enough to get it off without lifting it.

    EDIT: Piece of cake. I just lifted the frame an inch or two and was able to squeak under and get it off.
    Last edited by Previologist; 11-25-2023 at 11:17 AM.

  9. #9
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    Re: oil sensor wiring

    My vote is to give yourself a break until it's a more comfortable situation to deal with (how do you even know the donor sensor isn't going to give you trouble?). Tie up the wiring somehow, put some electrical tape over the connector ends, pull the reserve oil pump power connector, and check manually until a warm spell. I'm sure the van will demand your attention to something else before too long, as all aged vehicles tend to do
    "If you find yourself holding a sledgehammer or a crowbar, it's time for a break."

  10. #10
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    Re: oil sensor wiring

    Sorry, missed your edit. I suppose a Previa owner tends to be the determined type...
    "If you find yourself holding a sledgehammer or a crowbar, it's time for a break."

  11. #11
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    Re: oil sensor wiring

    Quote Originally Posted by man_btc View Post
    My vote is to give yourself a break until it's a more comfortable situation to deal with (how do you even know the donor sensor isn't going to give you trouble?). Tie up the wiring somehow, put some electrical tape over the connector ends, pull the reserve oil pump power connector, and check manually until a warm spell. I'm sure the van will demand your attention to something else before too long, as all aged vehicles tend to do

    Actually that's probably what I will do anyway. I had been driving with the oil level light flashing and pump disconnected for months, and I wasn't worried. I only noticed the connector wires were broken recently, and foolishly thought "even though I don't care, this should be an easy fix."

    I just hooked up the connector from the 93 (the sensor itself came from the 93 three years ago) and the light is still flashing. So I am going to go back to ignoring it and find something more important to fix, which means my 4runner.

  12. #12
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    Re: oil sensor wiring

    Quote Originally Posted by Previologist View Post

    I just hooked up the connector from the 93 (the sensor itself came from the 93 three years ago) and the light is still flashing. .
    Um, no I didn't and no it isn't. I didn't snap the connector fully into place, but now I did and everything is working as it should.

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