Case IH 2921 – UCM: ZDC Controller Offline / CAN Bus Communication Timeout

The UCM has not received the UcSpeedSignals message from the ZDC controller for more than 500 milliseconds, indicating a CAN bus communication timeout where the ZDC controller is offline. This typically points to a loss of power to the ZDC controller, a break or short in the CAN bus wiring, or a failed ZDC module.

• Steiger T4B
• Steiger series
• Steiger 420
• Steiger 500
• Steiger AFS Connect

1. 1

   Verify system voltage is stable and between 9.5 V and 16.5 V

2. 2

   Check ZDC power supply fuses F-101 (5A) and F-102 (7.5A)

3. 3

   Inspect CAN bus wiring between the ZDC controller and the UCM for rubbed wires, shorts to ground, or open circuits

4. 4

   Inspect ZDC and UCM connectors for pushed pins, corrosion, or moisture intrusion

1. 1

   Turn off the ignition and disconnect the battery

   This prevents electrical spikes during the repair.

2. 2

   Locate the ZDC controller and the UCM

   Find both modules on the machine to begin testing.

3. 3

   Test fuses F-101 (5A) and F-102 (7.5A)

   If blown, replace them and retest the system. If they blow again immediately, trace the power wire for a short to ground.

4. 4

   Perform a continuity test on the CAN High and CAN Low wires

   Test the wiring between the ZDC and the UCM. Repair any damaged sections of the harness.

5. 5

   Verify ZDC controller ground

   Ensure that the ZDC controller is receiving a good ground connection.

6. 6

   Replace the ZDC controller

   If the fuses, wiring, power, and ground to the ZDC controller are all intact but the code persists, the ZDC controller itself has likely suffered an internal failure and must be replaced.

7. 7

   Clear fault codes and calibrate the new module

   After replacing the controller, use the Case IH EST (Electronic Service Tool) to clear the fault codes and calibrate/program the new module to the tractor.