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.
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.
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.
Can you email the links? I'm unable to open them through this website. My email is [email protected] And yes sir. A wiring schematic is exactly what I'm trying to find
Email on the way. Just checking - is Collin spelled with one "L" or two.? Just in case you mis-spelled it without realizing.
Thanks for doing this Nige!!! Jewels in your Crown.
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. Regards and best of luck
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..?
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
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.
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.
Makes sense in the usual twisted military logic I suppose.
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
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.
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...!!!
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.
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.
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..?
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?
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.
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.
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.
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.
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
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.
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
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. 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.
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.
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..?
Thanks for doing this Nige!!! Jewels in your Crown.
Definitely. His Crown is already loaded but we can all use more!!!!
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.
That's usually the way I find interesting stuff. Glad to know I'm not the only one. Cross-reference information is always useful.
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....
Also note they are cranking some impressive figures out of those engines. 700HP from a C13 for example.
Or 525 BHP from a C9.3. I'm sure they don't intend them to last too long.....