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Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 4291
Experience:  17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
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Need detailed wire diagram and expertise on cat 257 parking,

Customer Question

need detailed wire diagram and expertise on cat 257 parking, hydralic ecm and bypass info
If you do not have detailed expertise in this machine, do not answer
Submitted: 2 months ago.
Category: Construction and Road Equipment
Expert:  Dan replied 2 months ago.

Hi my name is***** will be glad to help. Check the harness and connector pins for corrosion or damage causing an open circuit in the park brake circuit and the safety interlock switch circuit. Check for fault codes in the ECM if you have Cat ET access or have pulled your fault codes. Let me know what you have for codes if you have them. If not, click on this link for the schematics and troubleshooting information to help you with testing and identifying the circuits. Let me know


Customer: replied 2 months ago.
I have removed the ECM and checked continuity per cat specs. The problem is the parking brake system randomly kicks on after running a few minutes. reset parking brake switch and it will run fine for a few minutes. There dosnt seem to be a specifice thing that trips it
A couple years ago it did the same thing and I think it was a little corrosion on one of the fuses. I didnt really find anything elseIm at a point with this machine that i just want to bypass the ECM controlling the solenoids that the parking brake circuit controlsThe parking brake solenoid is easy power to A958, but im having a harder time with right joystick -power to 998 orange and cant figure what and where controls power to left (transmision solenoid)I want to power these solenoids if I can and install my own safety switchThe machine has has a few other electrical issues and not worth new elect harness
Trying to find a bad wire or connection is a nightmare - especially intermittent issues
Expert:  Dan replied 2 months ago.

Thanks for the update. If the wiring harness tests out good with no corrosion, damage, or open circuits then, I recommend having the ECM bench tested and reflashed/reprogrammed as in some cases a software issue with the ECM can caus thes symptoms if the harness, solenoids, and switches test okay. Let me know

Customer: replied 2 months ago.
Ill call cat in am and see if I can send it to themGood ideaWhat activates left and right joysticks
I cant figure it out and its driving me crazy!
Expert:  Dan replied 2 months ago.

The ECM enables and disables the controls depending on the safety interlock switch status such as lap bar, seat and door switch if equipped. If the switches and harness are okay I would check the ECM. Let me know

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