Cat 257B Aux hydraulics only work in one direction

[Nige]

I also retested and the wiring from the switch to the ecm is working. So unless there is something outside of that simple circuit which affects how the ecm performs….. the ecm is bad. Correct?

Correct.

Could I not take those three wires that run out of the 12 pin connector by the switch, and bypass the ecm with those three completely, just have them run directly to the solenoids?

Unfortunately it will not work. As you measured earlier, the switch output voltage is: -
- 4.04-4.09 in center position
- 1.9 in down position
- 6.28 in up position
So if you hook the switch directly to the solenoids they will both be permamently powered.

And yes I know this is not a fix anyone would probably recommend. I would like to do it in a way that I could easily restore it to factory and replace the ecm down the road but not have to spend $1200 or more right now. Feel free to tell me if I’m totally wrong.

If you don't want to go to the expense of replacing the ECM at this time the only possibility is to unpin the wires 40, 42, & 58 from the ECM connector and wire them via some sort of spring-loaded centre biased toggle switch. You would need a 10A fused power supply to the switch, output would be on wire P978-GN for one solenoid and P979-YL for the other. You would need to connect the L998-OR common wire from both solenoids to machine frame ground.

To remove the wires from the ECM connector a Deutsch connector de-pinning tool is required. See this LINK but you can also get them elsewhere. Note that ythese tools are fragile and easy to break if too much force is used.
There are plenty of vides on Youtube showing how they are used. De-pinning the ECM connector and retaining the original pins on the wires means you could refit them if you replaced the ECM at some point.

 

[CotterFCattle]

What other functions does that ecm control?

 

[Nige]

What other functions does that ecm control?

Take a look on Page 13 of the schematic for the full list. Also note that there are certain signals (armrest switch, implement lockout switch) that are integrated with the Interlock ECM that is located right above the AUX ECM on the schematic.

 

[Nige]

Something that may interest the OP. In conversation with a contact who works for a Cat dealer he offered the information that in his experience the most common failure of the AUX Hyd Ctrl ECM is a loss of response to the thumbwheel switch in one or both directions. Make of that what you will.

 

[CotterFCattle]

Thank you that gives me a little more confidence. I forgot to report back but I bit the bullet and ordered an ECM. $1200 but they do offer returns surprisingly. I am crossing my fingers that fixes it. Even with all our testing I feel nervous!

 

[Chrisso]

$1200 but they do offer returns surprisingly

I'd get that in writing. Usually once you open the box you're done for with ECMs.

I reckon that ECM will come without software in it, which you will need. Something to think about.

 

[CotterFCattle]

I have a feeling there will be some sort of cover on the plug that, once tampered with, will void returns. I made sure to buy one preprogrammed, I gave them my machine info so they could program. Crossing my fingers, I will let you know the result!

 

[Mobiltech]

Most cat ecm’s have a timed test mode . I can’t remember how many hours it is but if you remove it from the machine within those hours it can be returned .

 

[Chrisso]

I made sure to buy one preprogrammed, I gave them my machine info so they could program.

In that case you should be ok.

 

[CotterFCattle]

Hey everyone just wanted to give an update. My new ecm came, I plugged it in, and it works like a dream cause glad our diagnostics panned out!

Thanks for your help, hopefully with having the resolution and everything someone else can use this thread to fix theirs.

Also just fyi….. a remanufactured ecm from cat was 4000 unprogrammed. I got one from an independent company that works on ecms for $1400 programmed and ready to go.

Thanks guys!

 

[Chrisso]

Also just fyi….. a remanufactured ecm from cat was 4000 unprogrammed. I got one from an independent company that works on ecms for $1400 programmed and ready to go.

If the new ECM works well why not give them a plug and share where you bought it from? Sounds like good value to me. Might help out the next person.