Case IH 12021 – INST / INST2: Communications Lost with Auxiliary Controller

The CAN bus communication network has lost contact between the main instrumentation and the auxiliary/remote hydraulic controller.

• MX Magnum
• STX Steiger
• Case IH MX Magnum Series (MX210, MX230, MX255, MX285)
• Case IH TG Series
• Case IH Puma Series (Puma 125)

1. 1

   Check data bus connections between the instrumentation and the remote hydraulic controller.

2. 2

   Verify that the main harness connectors (such as connector C055) are fully seated and locked.

3. 3

   Check the unswitched power, switched power, and clean ground circuits going to the Auxiliary Controller to ensure the module is actually powering up.

4. 4

   Inspect the wiring harness routing near the rear housing/range housing seam for chafing, pinches, or rodent damage.

1. 1

   Power Down

   Turn off the tractor, remove the key, and disconnect the battery to prevent electrical spikes.

2. 2

   Locate the Controller

   Locate the remote auxiliary controller. On many Magnum models, this requires accessing the rear housing area or the left-side engine compartment fuse/relay area depending on the specific harness routing.

3. 3

   Disconnect and Inspect

   Disconnect the wire harness from the remote auxiliary controller. Inspect the pins on both the controller and the harness connector for corrosion, pushed-out pins, or moisture intrusion.

4. 4

   Clean and Re-seat

   If minor corrosion is found, clean the contacts with electrical contact cleaner, apply dielectric grease, and firmly reconnect the harness.

5. 5

   Test CAN Continuity

   If the connection is clean, use a multimeter to check the continuity of the CAN bus wires between the INST controller and the Auxiliary controller. Repair any open or shorted wires in the harness.

6. 6

   Replace Controller

   If the wiring, power, and ground are all intact but communication cannot be established, the auxiliary controller has suffered an internal failure and must be replaced.

7. 7

   Reassembly and Clearing

   Reconnect the battery, turn the key on, and use a diagnostic tool or the tractor's instrument display to clear the INST fault codes. Test the remote hydraulic functions to ensure the code does not return.