Case IH 1992-02 - UCM – UCM: Lost CAN bus communication with rear hydraulic remote valve #7 pilot head

The UCM (Universal Control Module) has lost CAN bus communication with the electronic pilot head actuator for rear hydraulic remote valve #7. When the UCM loses communication with this specific pilot head, the #7 remote valve is disabled. In some cases, a shorted pilot head can crash the entire local CAN bus, taking other remotes offline as well.

• MAGNUM AFS Connect
• Steiger / Quadtrac (350, 400, 450, 470, 500, 580)
• Magnum (210, 225, 280, 340)
• Puma (185, 200, 220, 240)
• Optum (270, 300)

1. 1

   Visual Inspection: Inspect the wiring harness and connector at the #7 rear remote pilot head for dirt, moisture ingress, corrosion, or physical damage.

2. 2

   CAN Bus Resistance Test: Disconnect the #7 pilot head connector. Using a multimeter, check the resistance of the CAN wiring between terminals 2 and 3 (typically the blue and red wires). It should be approximately 120 Ω (or 60 Ω across the whole bus). If not, there is a fault in the wiring harness.

3. 3

   Voltage Check: Turn the ignition ON and verify that the pilot head is receiving proper operating voltage and has a clean ground at the connector.

4. 4

   Component Swap Test: Swap the #7 pilot head with an adjacent, known-good remote pilot head (e.g., #5 or #6). If the fault code follows the pilot head to the new location, the pilot head's internal controller has failed. If the fault remains at #7, the issue is in the tractor's wiring harness or the UCM.

1. 1

   Depressurize

   Turn off the tractor, lower all implements, and relieve hydraulic system pressure.

2. 2

   Disconnect

   Unplug the electrical harness connector from the #7 rear pilot head.

3. 3

   Remove

   Remove the hex-headed mounting screws securing the pilot head to the rear axle/remote valve housing.

4. 4

   Replace

   Remove the faulty pilot head assembly and install the new OEM pilot head. Ensure the mating surfaces and O-rings are clean.

5. 5

   Reassemble

   Torque the mounting screws to the OEM specified value and reconnect the electrical harness.

6. 6

   Calibrate

   Perform the EHR (Electro-Hydraulic Remote) valve calibration procedure. Access the tractor's diagnostic menu (often under the 'HK Menu' -> 'Channel 1 Valve Calibration') to register the new pilot head with the UCM and teach it the valve's mechanical limits.