Cat 257B Aux hydraulics only work in one direction

[CotterFCattle]

Hello all,

I have a cat 257b serial # SLK05001 I purchased a while back. I am having trouble with the aux hydraulics for a grapple, etc. This is a high flow machine so it has a thumb wheel. Here is what it is doing:

- Pull the thumb wheel down and hydraulics function correctly. With no tool on it labors trying to push oil.
- Release thumb wheel and machine keeps laboring.
- Push thumb wheel up and it quits.
-Pushing up does not make it push oil in other direction.

Please note that I DID try replacing the thumb wheel. I was positive that was the problem, and it was not. Luckily CAT let me return an $1150 handle....

I have tested the solenoids on the valve and they both show the same amount of resistance with a multimeter.

I have used a test light to verify that the connector to one solenoid is receiving power, but the other is not.

Therefore, I have an issue somewhere between the switch harness and the wire that connects to the solenoid. Where should I go next?

I saw that there is something in troubleshooting info from cat about what to do if the switch only works in one direction, but I have not been able to find it.

Thanks!

 

[Nige]

Do you have an electrical schematic.? It would probably be useful.

 

[Nige]

- Pull the thumb wheel down and hydraulics function correctly. With no tool on it labors trying to push oil.
- Release thumb wheel and machine keeps laboring.
- Push thumb wheel up and it quits.
-Pushing up does not make it push oil in other direction.

Let me get this right. So rolling the thumbwheel back to the neutral (centre) position does not shut off the AUX hydraulics and you have to roll it all the way in the other direction to get the AUX to shut off.?

Have you inspected the electrical connections on the ECM yet.? what sort of condition are they in.?

 

[CotterFCattle]

I have a partial schematic but not the full one.

Correct, merely releasing the thumb wheel does not shut it off. I have to go into the other direction or the machine will continue pushing oil.

No I have not, where is the ECM located? I got lost tracing the wires through the harness.

 

[Nige]

No I have not, where is the ECM located? I got lost tracing the wires through the harness.

I’ll try to find some diagrams of the ECM location and send you a full electrical schematic as well.

One of the first tests to do when you have the schematic will be to measure the output voltage from the thumbwheel switch in various positions.

 

[CotterFCattle]

That would be super helpful thank you!

 

[CotterFCattle]

Are you saying you still suspect a switch problem even though I put a new handle and switch on? It still seems like a switch issue except for that, but obviously there is some amount of signal happening when I push the thumb wheel up....

 

[Nige]

Are you saying you still suspect a switch problem even though I put a new handle and switch on? It still seems like a switch issue except for that, but obviously there is some amount of signal happening when I push the thumb wheel up....

Not necessarily. I was interested to see the switch output and then go to the ECM and confirm that what’s coming out of the switch is actually making it to its destination.

EDIT: Here's the chassis wiring. The ECM for the Work Tool Control is #20, mounted in the RH footwell.

 

[CotterFCattle]

Ok thank you that makes sense. Do you have any idea what parameters I should be looking for out of the switch?

 

[Nige]

Locate the 12-pin connector directly below the joystick. The pin numbers will be moulded on to both halves of the connector. You'll need attachments for your multimeter to measure voltage in the pins without unplugging the connector.
With key ON engine OFF measure the voltage between Pins 1 & 2. It should be 8.0 +/- 0.5v.
Measure the voltage between Pins 3 & 2 with the thumbwheel switch in the centre, then with it rolled all the way in both directions. Report your findings.

 

[Nige]

Sorry I failed to mention that the measurements should be repeatable to within +/-0.1v no matter how many times you do them. So for example if the first voltage measurement for the centre position of the thumbwheel is 4.55v then if you measure it a dozen times all the others should be in the range between 4.45 & 4.65v. The same tolerance range applies to the maximum and minimum measurements.

Once you have the results at the switch move to the ECM and measure the voltage arriving there on Pins 52 & 53. These are the same wires P996 Green & P997 Brown that come from Pins 2 & 3 of the 12-pin connector at the switch. Again measure 3 positions of the switch and record your results.

 

[CotterFCattle]

Ok I will do that. So you are saying 52 and 53 are the ones going INTO the exam right? Or out of?

 

[Nige]

So you are saying 52 and 53 are the ones going INTO the exam right?

Correct. If you follow wire numbers P996 & P997 on the schematic from the thumbwheel switch they go to Pins 52 & 53 of the AUX ECM. We want to make sure the signals are good going INTO the ECM before we start looking more deeply into what's coming out.

 

[CotterFCattle]

ok, we tested as you specified. Pins 2 and 3 deliver:
- 4.04-4.09 in center position
- 1.9 in down position
- 6.28 in up position

Testing between pins 52 and 53 I get the exact same numbers with several repetitions and very minimal change.

What pins do I use to check coming out of the ecm?

Philip

 

[Nige]

So those numbers confirm that there is nothing wrong with the roller switch or the wiring as far as the ECM and that the required signals are getting to it.

On the output side you need to measure between Pins 40 & 42, then between Pins 58 & 42. Pin 42 is common.
One of those pairs powers the AUX A1 solenoid and the other pair powers AUX A2. I don't know which way the roller switch has to move to power which pair but I'm sure you'll figure it out.
Test with key switch ON, engine OFF. All wiring harness connector remain plugged in.
Test both at the ECM end and the solenoid end. Use the wire colours/numbers at the solenoid end to identify which is which.
You will need the cab raised for the second test. The AUX solenoids are mounted on opposite ends of the main implement control valve.

 

[CotterFCattle]

Ok these numbers line up with what I am seeing as well.

Between 40 and 42 it shows nothing in the center position. When I push the switch down it shows -2.65. When I release the button it does not return to 0. When I push the button up it returns to 0

Between 42 and 58 it shows 0 with the switch in the center position or up position. In the down position it shows a slight negative of -.029

So this means my ecm is bad??

 

[Nige]

So this means my ecm is bad??

It wouldn't surprise me.

Try disconnecting the machine harness connectors A-C24 & A-C25 at the A1 & A2 solenoids and repeat the tests. See if the results change.

 

[CotterFCattle]

Ok I will do that. So you’re saying if it worked differently with those disconnected there could be a solenoid issue right?

What is that specific ecm called and what is the part number for it?

 

[Tyler d4c]

Those handles are 1150 dollars now

 

[Nige]

So you’re saying if it worked differently with those disconnected there could be a solenoid issue right?

Potentially yes. while you are in there disconnecting A-C24 & A-C25 also test the resistance of the solenoid coils for A1 & A2. It should be 2.2 ± 0.2 ohms.

What is that specific ecm called and what is the part number for it?

It's called the Aux Hyd Control ECM and the Part Number I see for it is 216-0658. There may be a newer Part Number than that and there also might be the opportunity for a Reman ECM which would have a Part Number something like 10Rxxxx or 20Rxxxx. You would have to ask your dealer Parts Dept. Before condemning an ECM it's worthwhile doing all the tests that can be thought up, and few more besides, mostly because of the cost.

I take it from your OP that the AUX function has never worked since you have owned the machine.?