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120M Event Code 127-3 Trans Oil Pressure Voltage Above Normal

Discussion in 'Motor Graders' started by MarineHEmech, Mar 13, 2020.

  1. MarineHEmech

    MarineHEmech Member

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    I'm new here but i have high hopes. I really need help. I'm a Marine Corps HE mechanic and I'm working on this Cat 120M motorgrader that keeps this code 127-3 saying the transmission oil pressure sensor voltage is about normal. My problem is that i have no idea where it is located on the trans and how to test it. None of my technical manuals have any information on this code at all and it's had me stumped for the past week. This gear is leaving to go on a deployment really soon and i need it serviceable ASAP. The serial number is NJD 00136. Thanks in advance for any information.
     
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  2. Nige

    Nige Senior Member

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    What you have is a Diagnostic Code (Voltage Above Normal) rather than an Event Code as you state in your OP
    Is the attached diagnostic procedure any help.?
    I'll find the location of the sensor and post it up.
    I can also send you the Electrical Schematic for the machine if that would help.
     

    Attached Files:

    Last edited: Mar 13, 2020
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  3. Nige

    Nige Senior Member

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    Here's the deal. There is no electrical schematic for the NJD-prefix machine.
    I found the pressure sensor on another version of the 120M. I can't see it being in a different place on your machine.
    Look for Item 11 on the attached Parts List.
     

    Attached Files:

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  4. MarineHEmech

    MarineHEmech Member

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    Can you email the links? I'm unable to open them through this website.
    My email is klein.collin@gmail.com
    And yes sir. A wiring schematic is exactly what I'm trying to find
     
  5. Nige

    Nige Senior Member

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    Email on the way.
    Just checking - is Collin spelled with one "L" or two.? Just in case you mis-spelled it without realizing.
     
    Last edited: Mar 13, 2020
  6. ovrszd

    ovrszd Senior Member

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    Thanks for doing this Nige!!!

    Jewels in your Crown.
     
  7. Mark250

    Mark250 Senior Member

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    Hi,if you cant figure out the problem in time to deploy, I might have a solution for you
    The transmission pump pressure sensor is used on the cold start parasitic load reduction feature which is an option ( Not sure about Military version 120M)
    and being an option it can be disabled in CAT ET see below
    I am assuming you have the military version of CAT ET so I don't know what level of access you have, but it is worth a shot if you get stuck and the weather is reasonable.
    upload_2020-3-14_17-43-52.png

    Regards and best of luck
     
  8. Nige

    Nige Senior Member

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    Yes, if the weather is going to be warm where this machine will be deployed then there will be no reason to be worried about parasitic load on "cold startup" therefore the feature could be disabled using ET if the Diagnostic Code cannot be successfully troubleshot before you have to ship it out. That would at least keep the operator from being distracted by flashing lights & warnings.

    Mark, a question for you. There is no electrical schematic for the NJD-prefix machine in the system, in fact none of the military versions of the 120M have schematics available which struck me as somewhat strange. As far as I can see the basic electrical schematic for all 120M AWD machines built around the same time frame 19/Jan/2011 ought to be broadly similar, especially on something as basic as the transmission pump sensor wiring. Would you agree..?
     
  9. Mark250

    Mark250 Senior Member

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    Nige, it has always been difficult to get that info. Over the years I have come across a few surplus machines and they have been not that much different than other M's out there.
    I don't know the reasoning why that info is not available for the military Machines ,but I would like to
     
  10. Nige

    Nige Senior Member

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    That was my thinking also, especially in something as basic as the transmission pump and the pressure sensor.
    I found a 120M AWD S/N B9W00209, built 1 day prior to the OP's machine NJD00136 in January 2011.

    As far as I can see the basic parts of the electrical wiring appear to be the same for both machines, when I look at the rear frame wiring (which is where the trans pump pressure sensor is located) the parts are to all intents & purposes the same despite the groups being organized a little differently between the two machines which complicates comparisons.
    Even the transmission pump is the same is as the CZM-prefix of the transmission. Trans S/N installed in B9W00209 - CZM08491, in NJD00136 - CZM08496, only five Serial Numbers apart. See below.

    upload_2020-3-15_0-40-13.png

    upload_2020-3-15_0-40-54.png
     
  11. John C.

    John C. Senior Member

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    In my experience in the military, some pencil neck civilian at a supply center misinterpreted a paragraph in some obscure policy and procedure manual and classified all technical information having to do the the operation, maintenance and repair of the subject motor grader. Obtaining the information required at least an O4 officer with top secret clearance to make a request to Pentagon with an explanation of why that information was needed.
     
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  12. Nige

    Nige Senior Member

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    Makes sense in the usual twisted military logic I suppose.
     
  13. MarineHEmech

    MarineHEmech Member

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    Thank you all for all your help and input. Never thought I'd learn so much in a short amount of time. Nige, the schematics you sent are almost identical to this machine. However, the wires for the sensor do something slightly different frkm what the schematic said. On the diagram, the green wire is 24 Volts, the black wire is ground, and the brown wire is signal. I used a multimeter on the grader to test the wires and each wire performed the task of the other wire. So the green wire was ground, the black wire was signal, but the brown wire was 5 volts rather than 24. This has me all sorts of confused. Maybe when the other mech swapped the wiring harness, they hooked some wires up wrong or something. I thought about just popping the pins out of the connector and switching them in hopes that that would work. I still don't exactly know why it's only getting 5 out of the 24 volts. Any ideas?
    Thanks gents
     
  14. Nige

    Nige Senior Member

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    Sensors don’t work on battery voltage. They get a stabilized voltage produced in the ECM. This can be either 5, 8, or 10V depending on the sensor type. Chase the sensor power supply wire back to the ECM on the schematic and you should find that the supply pin is labelled with what the voltage ought to be.

    As I said I couldn’t guarantee that schematic I sent you would be correct as regards wire numbers and colors, but the theory of how the sensor works should be the same whatever colour wires are feeding it.

    Also when you are checking voltages check them to the sensor ground wire that will ground back to the ECM, not to machine frame ground.
     
  15. Nige

    Nige Senior Member

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    Based on the comment that another mechanic was working on this machine before you may have to check every main wire connector between the ECM and the sensor to ensure that nothing has been crossed over somewhere obscure. Two wrongs don’t necessarily make a right, especially where electronics are concerned.

    If someone else has been there before - assume nothing...!!!
     
  16. Nige

    Nige Senior Member

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    Another thought. If the sensor has been replaced and the replacement is an incorrect part number the wire connections to the black plug could be pinned differently. Or it could be the correct P/N sensor simply manufactured wrong.
     
  17. Nige

    Nige Senior Member

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    Randonm thoughts in no particular order.

    a) Have you checked the Part Number of the installed sensor.? I can see two possible options, 221-3412 or 463-8243. Both are equally acceptable, one is simply a newer version of the other.
    b) You should be able to find the letters A, B, & C on the back of each half of both the connectors (machine harness, jumper harness, and sensor pigtails) in the illustration below. Does the letter location of the wires at both 3-pin connectors tally with the schematic.?
    c) Were you measuring the 5V by back-probing with a DMM at CONN 43 or did you have the sensor wiring disconnected..? In the case of a 24V sensor you can actually measure voltage to ground with it disconnected.
    upload_2020-3-17_16-7-39.png
     
  18. Nige

    Nige Senior Member

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    OK, I'll bite. Can you find information regarding what EXACTLY was done to the machine before you were assigned to it..?

    Which wiring harness did "the other mech" swap.? Because there is no harness connector between CONN 43 and the ECM - at least there isn't one shown on the Schematic.

    Another question. Where exactly are you testing with your DMM..? The connector right next to the sensor or the one a couple of feet away marked #9 on the illustration below.? In fact do you even have the harness marked #2 on your machine or does the wiring from the sensor connector dive straight into the main machine harness as shown by the arrow in the 2nd illustration..?

    upload_2020-3-18_0-50-43.png upload_2020-3-18_0-55-40.png
     
  19. MarineHEmech

    MarineHEmech Member

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    Hey. I finally got our CAT ET to work on our computer. Only took forever. I have it all open and have the item highlighted. However, there isn't an option (or i just don't see it) to disable it. Any additional help?
     
  20. Nige

    Nige Senior Member

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    If you click on that line it will highlight blue like Mark250 showed in post #7 above.
    Look at the bottom of the ET screen for the "change" button and click on it.
    Different versions of ET over the years have done it differently (not sure which one you have) but you should either get a drop-down menu that you can select from, or a highlighted cell that you can use the up/down arrow keys to illustrate the options available. In your case the options should only be either "Installed" or "Not Installed".

    Found a screen shot. This is not the latest ET so your screen may look a bit different, but when you highlight the parameter the Change button should change status from greyed-out as it appears in this screen shot to "normal". The same appearance that the "Collapse All" button has in the screen shot.

    upload_2020-3-20_14-48-14.png
     
    Last edited: Mar 20, 2020