Case IH F-3507-06 - ECU – Engine Control Unit (ECU): ECU 12/24-volt actuator supply 2 (UB3 supply) short to ground failure

The voltage on the ECU 12/24-volt actuator supply 2 (UB3 supply) circuit is being unexpectedly pulled to 0V (grounded). This condition prevents the actuators powered by this circuit from receiving the necessary voltage to function.

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• Axial-Flow Combines

1. 1

   Harness Inspection: Inspect the engine wiring harness connected to the ECU (specifically tracing the wires from Bosch MD1CE101 pins 5.06, 5.09, and 6.25). Look for chafing, rubbing, or pinched wires that are making contact with the machine's chassis or engine block.

2. 2

   Actuator Isolation: Disconnect the actuators powered by the UB3 / Supply 2 circuit one at a time. If the short-to-ground fault status changes to an open circuit or disappears when a specific actuator is unplugged, that actuator has an internal short.

3. 3

   Connector Check: Inspect the ECU harness connectors for moisture, corrosion, or bent pins that could be bridging the supply voltage to a ground pin.

4. 4

   Continuity Test: With the battery disconnected and the ECU unplugged, use a multimeter to measure the resistance to ground on the UB3 supply wire. It should read as an open circuit (infinite resistance). If there is continuity to ground, the harness itself is shorted.

1. 1

   Disconnect battery

   Turn off the ignition and disconnect the machine's battery to prevent electrical damage during the repair.

2. 2

   Disconnect wiring harness

   Disconnect the wiring harness from the ECU and the affected actuators on the UB3 circuit.

3. 3

   Repair or replace wiring harness

   If the harness is damaged: Repair the chafed/shorted section of the wiring harness using an OEM-approved wiring repair kit, or replace the harness section if the damage is extensive.

4. 4

   Replace shorted actuator

   If an actuator is shorted: Replace the specific engine actuator that failed the isolation test.

5. 5

   Replace ECU

   If the ECU is internally shorted: If the harness and all actuators test perfectly fine but the UB3 pin on the ECU itself is shorted to ground internally, the ECU must be replaced.

6. 6

   Reconnect components

   Reconnect all components and the battery.

7. 7

   Clear fault codes and verify repair

   Use a diagnostic tool (such as the CNH EST) to clear the fault codes and run the engine to verify the repair.