Looking for a wiring diagram for my cat 257b ser number 02052. I’m pretty sure I have a bad auxiliary hydraulics pcm but would like to confirm some more tests. I found a wiring diagram for a 257 on here but some of the wires I need to test are not the same as what are on my 257B. The issue i am having is when I went to use it with my grapple attachment it had no aux hydraulics. I noticed also that the interlock override light is dimly lit at all times with the key on and while operating. I’ve tested the rocker switch and the voltages are where they should be. I did find the wire at the pcm that grounds the interlock override light and when I put ground to it the light comes on at normal brightness. I’m assuming if the computer is giving it a high resistance ground hence the dim light it should be something internally with the pcm.
You need to confirm that the three letters prior to the "02052" are SLK. If they are then everything below applies to your machine. This THREAD pretty well covers everything you might need. During the course of the diagnostic errors in the troubleshooting procedure were found that you need to be aware of. Specifically you need to read Posts #55, 56, & 58 on Page 3 and use that information with RENR6417. You will need RENR6417-01, REHR6419-06, and the document on the Interlock electronic Control. You can download them from the same thread.
Thank you Nige, I’ll try to get back to this today and post some results.
I’m following the one issue that is obvious which is the interlock override that is on dimly at all times with key on. When checking the pcm circuit that grounds the light I get 7.78 volts out of the pcm with the light unhooked. Shouldn’t this circuit be 0 volts. I’ve never seen a pcm circuit that supplies ground to something have voltage at it. I’m gonna try to find another pcm controlled light and see if it also has voltage. Thank you Nige for your invaluable assistance in this.
It may not be the case with this particular control but quite a few circuits I have come across where the ECM supplies the ground to complete the circuit. Try going through the testing procedure in RENR6417 in the order in which it is laid down. You might be surprised.
Found two other lights pcm controlled but the pcm supplies voltage so this comparison won’t work. There is a resistor part number 167-7801 REV 0 attached in the wiring to the interlock override lamp that i thought may be causing an issue but unhooked it and light still on dimly unless this could be an issue. I don’t see it in the diagram for the right side dash lamps. It reads 381 ohms. I’m gonna start testing the door switch now that I have the correct wiring diagram and see what I find with that. It doesn’t seem like it would cause the auxiliary hydraulics from working as this would disable all boom hydraulic functions. This is definitely one of those takes as long as it takes to diagnose situations. I’ve got way too many hours into this thing. But I could be a test away from finding the problem. The light at the end of the tunnel could be right around a corner of this tunnel.
During this test it had me skip to step 9 and then continued to step 10 that had me measure resistance from 29 and 68. 10 ohms. This machine has had no issue with the parking light or armrest light. It operates fine except the aux hydraulics does not work and the interlock override light stays on dimly.
I’m not sure whether it’s relevant but did you look at the posts in the linked thread where errors were found in the RENR6417 test procedure.?
I’d like to start off with a huge thank you to you Nige, your help has been priceless. Yes I did look over the posts you sent in the link and performed those tests. I have been basically testing everything I can from the ecms directly. I can operate the a and b solenoids with ground supplied at the pcm. They click and sound normal. Do you have a diagnostic chart for aux hydraulics only inoperative? What would make the interlock override light come on dimly? I found a resistor in the circuit to the light that is plugged in behind the rh dash light assembly but I don’t see anything about it in the wiring diagram. I’ve unplugged the resistor and the light remains on without it so I’m assuming it’s not the culprit. I’ve checked the circuit to and from the light and it all checks ok. I’ve went down all the diagnostics on here I could find but everything I’ve found is for issues that coincide with the interlock lights flashing or on. I just checked the auxiliary bleed valve and that tests ok. It sends a ground signal to the ecm when pressed and the only way I can see this cause an issue is if it was grounded all the time. I’ve spent days on this and am starting to think I need a CAT ET to see what the ecm is seeing that isn’t allowing aux hydraulics to work. I keeping coming to the conclusion that the aux ecm is bad but would like to exhaust any other tests before I gamble with a new ecm.
Have you tested the output from the thumbwheel roller yet.? If not I suggest that you do it by back probe in the connector under the joystick and also at the AUX ECM connector. That way you confirm what is coming out of the switch is also going into the ECM. The output will be a DC voltage that varies depending on the roller position. Take measurements in the centre and rolled to both extremes.
I performed this early on following a thread on HE. The thumb roller switch tested at 2.09v forward, 4.08 center, 5.97 rear. It was consistent and only fluctuated a thousand of a volt. Used min max on meter and never fell above or below. Have 8 volts at the supply.
Any ideas on what that resistor behind the dash is? I’ll send a pic. I also have a question on another item on this 257B. I’ll send a pic also of a valve located on the right rear of the machine that I don’t know what it’s used for. This could be possibly related to the aux controls inoperative but it has a plugin and a 3rd coupler by the aux couplers I’ve never used it and I’m not even sure what it is for ,i was assuming a snow blower attachment. It has a 4 button control handle on the left side of the machine which seems strange cause while using this handle you wouldn’t be able to move the machine at the same time I bought it from a large farm operation Could there be a control or issue with this that could effect the aux controls?
No problem with the thumb roller then. Did you test at both the output of the roller switch and the ECM input as I suggested.? Just need to confirm that what is leaving the switch is actually arriving at the ECM.
167-7801 should measure at 390 ohms. Do you have any wire colours/numbers that come into the resistor connector.? Not Pink and Yellow by any chance.?
Can you find any tags with Part Numbers on them in the area you circled.? There may even be a P/N stamped on the mounting bracket.
I performed the test at the ecm by backprobing.
Can you confirm the full machine Serial Number please. I'm a bit concerned that the electrical schematic that is being used for the troubleshooting might be the wrong one.
This one measures 381 ohms. Here is how it’s wired in. There are two connectors for this resistor with only one being used. The other one is for the MSS security lamp which I don’t believe this machine has. It has 12 volts to it from the white wire pin 1 and then goes to the yellow wire.
CAT0257BASLK02052
I was originally thinking this was for the 3rd hydraulic coupler but it’s for the hydraulic quick coupler. I believe the valve in the photo is to disable the hydraulic quick coupler to allow for tool removal in case of hydraulic coupler failure.
You are correct. It’s for a hydraulic coupler with manual lowering control.
Sorry for the late response. The problem did end up being the auxiliary pcm. Bought one ecm on Amazon but didn’t change anything. Thankful for easy returns on Amazon and a full refund it was returned. Second attempt was to send pcm for repair and after two times back and forth shipping to remanufacturer in Texas still no change. Third attempt was to try a used one. Found a used one fairly close to me and still no change. Ended up hauling it to a dealer to have them hook up the CAT scanner to see what was going on. The tech reprogrammed the used pcm and the remanufactured pcm and both worked fine after that. PCM was the culprit as I suspected. These machines have two options for the auxiliary control. One has two buttons for aux control and the other has a roller/rocker switch and they need the correct programming to work. Thank you Nige for the help. Hopefully this helps someone else out.
Correct. The parameter for the RH joystick (buttons or roller) is a selectable option in the Configuration screen. If the ECM has the wrong option selected for the machine configuration the control won't work.