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catmastertech, Technician
Category: Construction and Road Equipment
Satisfied Customers: 2346
Experience:  Field service technician for CAT 19 years.
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Is there a test for the auxiliary hydraulics rocker or

Customer Question

is there a test for the auxiliary hydraulics rocker or enable switch that I can perform without the Cat diagnostic machine ?
JA: What is the complete model and serial number of your machine?
Customer: 247b2, cat0247bhmtl05214
JA: Are you fixing this yourself? What have you tried so far?
Customer: tested all hydraulics, we are only getting 1 1/2 volts to the coils for the aux hyds. we have 8 volts at the rocker switch on the white wire and a constant 4 volts on the yellow wire
JA: Anything else you want the equipment mechanic to know before I connect you?
Customer: all relays and fuses are good
Submitted: 9 months ago.
Category: Construction and Road Equipment
Expert:  catmastertech replied 9 months ago.


The short answer to your question is no. You need CAT ET to test the circuit and verify the ECM is working.

However, you can take your questionable ECM and install it in a known working machine. If it works correctly, then you will know it is not the issue. (Never install a good ECM into a questionable machine or you may end up with two failed ECMs.)

I have CAT ET so, I have not tried testing any other way. I would suggest you follow the attached information to verify at least some of your wiring. You may see better results if you try to read the coil circuit in amps than voltage. I have found sometimes A/C voltage reads are better when working with ECMs as their output is pulse width modulate voltage.

(Of course, you will need to move the rocker instead of pushing the A1 or A2 switches.)

Let me know what you find and if you need more help. I will be glad to help all I can.



Expert:  catmastertech replied 9 months ago.

Hello again,

Where you able to test any of the circuits?

Did you try swapping the ECM to a different machine?

Can I help you with anything on this issue?

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