Case IH 518315-02 - UCM – UCM: Hydraulic lock switch - plausibility check / disagreement

The hydraulic lock switch is a safety control used to lock out the hydraulic remote valves, preventing accidental movement of implements. A 'disagreement' or 'plausibility check' failure means that the dual-channel contacts inside the switch are sending conflicting signals to the control module (e.g., one circuit indicates the switch is locked while the other indicates it is unlocked). The module cannot determine the true position of the switch, so it logs a fault and typically defaults to a locked/safe state.

• MAGNUM AFS Connect
• Magnum 400 AFS Connect
• Magnum 250-380 series

1. 1

   Connect the Case IH EST to the diagnostic connector to monitor the live status of the UCM and the hydraulic lock switch. Observe if the switch state toggles correctly or shows an 'invalid' state when pressed.

2. 2

   Check the physical hydraulic lock switch (located on the operator's armrest/console) for sticking, physical damage, or debris preventing full travel.

3. 3

   Inspect the wiring harness between the hydraulic lock switch and the UCM. Look for chafed wires, loose connector pins, or corrosion that could cause high resistance or a short circuit on one of the switch's signal wires.

4. 4

   Unplug the switch and use a multimeter to test the internal contacts. Both channels should transition simultaneously when the switch is toggled. If one contact remains open or closed regardless of switch position, the switch has failed internally.

1. 1

   Power Down

   Turn off the tractor key switch and disconnect battery power to prevent accidental short circuits during repair.

2. 2

   Access the Switch

   Carefully pry or unscrew the trim panel on the armrest/console to access the underside of the hydraulic lock switch.

3. 3

   Disconnect and Replace (if faulty)

   Unplug the electrical connector from the switch. If the switch failed the continuity test, remove the retaining clips/tabs and push the old switch out of the bezel. Snap the new OEM switch into place and reconnect the harness.

4. 4

   Harness Repair (if applicable)

   If the diagnostic checks revealed damaged wiring rather than a faulty switch, splice and heat-shrink the broken wires, or replace the damaged connector pins at the UCM or switch connector.

5. 5

   Reassembly and Clearing Codes

   Reinstall the armrest trim panels. Reconnect the battery, turn the key on, and use the EST (or the AFS Pro display diagnostics) to clear the 518315-02 fault code.

6. 6

   Verification

   Toggle the hydraulic lock switch to the 'LOCK' and 'UNLOCK' positions. Verify that the remote valves are properly disabled when locked and that the fault code does not return.