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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 was back probing the three pin connector at the sensor. And i was just told that the cab wiring harness was the one replaced. I figured that out when i was just killing time for a minute in the cab and realized that most of the switches didn't work. I asked why and apparently they had a brain dead mech do the replacement. So as far as i know based on the schematics, this shouldn't effect the trans.
     
  2. Nige

    Nige Senior Member

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    I'm not sure I agree with your thinking. If the sensor was powrered by stabilized voltage produced in the Power Train ECM I would tend to agree with you - the fact is it's powered by machine 24V from somewhere.
    Now the whole of the cab (the switches for example) is also powered by 24V, maybe from the same fuse or circuit breaker that powers the transmission pump pressure sensor. So working on that theory if something is wrong up top that could be the reason you're reading 5V rather than 24V down at the transmission pump pressure sensor.

    Here's a thought. Does the A/C work..? The same 124 wire that powers the pressure sensor also operates the A/C clutch relay, the solenoid and the low pressure switch. Follow the schematic from the same area as the pressure sensor and look for wires 124-FA263, and 124-FA248. If you only have 5V on those as well then your problem is coming from somewhere upstream, and despite the fact that I'm not a betting man I'll bet good money you find something screwed up in the cab where the harness was replaced.
     
  3. Nige

    Nige Senior Member

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    Following the schematic from Grid H-10 in the opposite direction wire 124-FA157 goes to CONN 9 in the cab firewall interface.
    Past CONN 9 it becomes 124-P399 (Page 13, Grid F-12) and heads off down Line H11 where it splices to 124-P147 at Grid I-14 and both become 124-P652 which actually goes to the HVAC Panel.

    So the supply wire is actually 124-P147 which comes from a 15A fuse # G15 in the fuse box. Try testing the input side of that fuse holder with the fuse pulled and see what voltage you have. If it is 24V then maybe pull all the connectors on the HVAC system that are fed by wire 124 and see if you now have 24V at the pump pressure sensor. After that start connecting things one at a time until your voltage drops to 5V. At that point whatever you just reconnected ought to be your problem area. I'm just wondering if you have a dodgy relay somewhere, there appear to be a number of them in that circuit.
     
  4. MarineHEmech

    MarineHEmech Member

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    I'll get right on that. I haven't even given much thought into testing the cab until today. But as it turns out, nothing for HVAC is working. Gonna do some digging and get back to you with what i find. Thanks a ton
     
  5. Nige

    Nige Senior Member

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    Start by pulling fuse # G15 in the fuse box and see what voltage is coming into it.
    Then TBH I'd replace the fuse and pull CONN 9. If you have 24V at CONN 9 outlet on the chassis side then you need to look "down below". As I said before that 124 wire feeds three components, all of which are for HVAC components apart from the pump pressure sensor.
     
  6. MarineHEmech

    MarineHEmech Member

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    So back to the original problem though is that the green 124 wire for the trans sensor isn't getting any power. The brown wire is the one getting the 5V. Also, my fuse block doesn't have anh fuses marked with "G". They are all F and the F15 is for the wiper. I've also already gone through the fuses today. All checks out
     
  7. Nige

    Nige Senior Member

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    OK, so your Green 124 isn't getting power, I thought it was the one getting 5V, but never mind.
    You need to follow the Green wire back all the way to the fuse box. It has to get it's power from somewhere if it is supposed to be supplied with 24V.
    I suggest you find CONN 9 on the cab firewall, locate the Green 124 wire at that point and work into the cab from there.
    Also look carefully at the wires leaving the fuse box. can you find 124 Green among them.? That way you could backtrack to which fuse it's coming from.
    I wasn't really talking about checking the fuses themselves, more about checking the power coming into them from the machine bus bar or main power relay and going out of them to the various machine systems.

    Don't get fazed to start with by the 5V on the signal wire. It could be nothing more than "pull up voltage" coming from the machine system. See below for what it is. Concentrate on locating the reason for the lack of power on 124 Green.

    upload_2020-3-20_19-7-38.png
    Under What Conditions Will you See "Pull Up Voltage" ?
    When the sensor is disconnected at the harness connector, the signal lead should be pulled high by the "pull up circuit". When a voltmeter is placed between the signal lead and signal ground on the harness. G
    uess what, that's exactly how you are measuring it, in the end of the machine harness connector with the sensor disconnected.
     
    Last edited: Mar 20, 2020
  8. MarineHEmech

    MarineHEmech Member

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    Thank you for the guidance. I'm going to have to get back at it monday morning. The shop won't let me stay later. I found the 124 wire in the fuse box. It is the A/C fuse. The fuse is not getting power so I'm goin to trace the wire to find where the break is along it.
     
  9. Nige

    Nige Senior Member

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    According to the schematic (which remember is not guaranteed to be 100% identical to the machine you are working on) there is a bus bar along the back side of the fuse box. So if one fuse is getting power then they all should.
    Maybe pull the fuse box apart and check the back side of it..?
     
  10. GabiJohnson

    GabiJohnson Member

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    Thanks for doing this Nige!!!

    Jewels in your Crown.
     
  11. ovrszd

    ovrszd Senior Member

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    Definitely. His Crown is already loaded but we can all use more!!!! :)
     
  12. Cmark

    Cmark Senior Member

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    Whilst searching SIS for something unrelated, I came across a military-civilian serial number cross reference table and thought of this thread. The equivalent prefix for a NJD machine is B9N. Document number is M0067238 if anyone is interested.

    NJD.jpg
     
    Mark250 and Nige like this.
  13. Nige

    Nige Senior Member

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    That's usually the way I find interesting stuff. Glad to know I'm not the only one.

    Cross-reference information is always useful.
     
  14. Nige

    Nige Senior Member

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    After digesting the information a couple of things I noted.....
    1. It was only published a month ago. I wonder why that was.? Ex-military machines have been around in the commercial market for a long time now.
    2. Amazing how many military variants of what on the face of it appear to be run-of-the-mill commerical machines have no commercial equivalent. Those models must have cost the military a pretty penny....o_Oo_O
     
  15. Cmark

    Cmark Senior Member

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    Also note they are cranking some impressive figures out of those engines. 700HP from a C13 for example.
     
  16. Nige

    Nige Senior Member

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    Or 525 BHP from a C9.3. I'm sure they don't intend them to last too long.....