Case IH F-3507-14 - ECU – Engine Control Unit (ECU): Supply UB2 short to ground failure

The Engine Control Unit has detected that the voltage supply circuit designated as "UB2" (which provides 12V or 24V power to specific engine or emissions actuators) has a direct short circuit to the chassis ground.

• MAGNUM AFS Connect
• Case IH Magnum AFS Connect Series Tractors
• Case IH Austoft 9900 Series Sugarcane Harvesters
• Case IH 240 Series Axial-Flow Combines

1. 1

   Inspect the engine wiring harness for chafing, melting, or pinched wires that could cause the UB2 power wire to touch the machine's frame or engine block.

2. 2

   Inspect the ECU harness connectors for water ingress, corrosion, or bent pins (specifically pins 2.05, 2.17, 2.18, and 2.19 on the Bosch MD1CE101 ECU).

3. 3

   Perform an actuator isolation test by disconnecting the actuators on this circuit one by one to see if the short clears.

4. 4

   With the battery disconnected, test for continuity between the UB2 supply pins at the ECU connector and a known good chassis ground.

1. 1

   Turn off the ignition key and disconnect the machine's battery

   This prevents electrical damage.

2. 2

   Locate the Engine ECU and carefully disconnect the main wiring harness.

3. 3

   Probe the UB2 supply pins (2.05, 2.17, 2.18, 2.19) on the harness side for continuity to ground.

   Use a digital multimeter.

4. 4

   Begin unplugging the actuators powered by this circuit one at a time.

   Perform this if a short to ground is present.

5. 5

   Monitor your multimeter and replace the faulty actuator if the short disappears.

   If the short to ground disappears immediately after unplugging a specific actuator, that actuator has failed internally.

6. 6

   Trace the harness back from the actuators to the ECU, locate the rubbed or melted section, and repair or replace.

   If all actuators are unplugged and the short to ground persists, the fault is in the wiring harness. Repair the wires using heat-shrink butt connectors or replace the harness section.

7. 7

   Reconnect all components, reconnect the battery, and clear the fault codes.

   Use a diagnostic tool.

8. 8

   Cycle the key and run the machine. Replace the ECU if the code immediately returns.

   If the wiring tests perfectly, and no actuators are shorted, the ECU itself has suffered an internal power supply failure and must be replaced.