Case IH 3878 – Engine Control Unit (ECU): Supply UB2 short circuit to battery failure

The control module has detected a short circuit to battery voltage (12V/24V) on the UB2 (Voltage Supply 2) circuit. The UB2 circuit is an internal power stage that provides voltage to specific engine actuators and relays (often designated as Actuator Supply 1).

• Steiger T4B
• 240 Series Axial-Flow Combines
• 7240
• 8240
• 9240
• Magnum
• Steiger
• Puma
• Farmall

1. 1

   Verify the code is active (emergency re-starts may be required to move the machine if it experienced a full power loss)

2. 2

   Visually inspect the engine wiring harness for chafing, melted insulation, or pinched wires, particularly where the harness routes near hot engine components or sharp brackets

3. 3

   Disconnect the ECU and use a digital multimeter to check the UB2 supply circuit for a short to battery voltage (Actuator Supply 1 corresponds to pins 2.08, 4.03, and 4.19 on the MD1CE101 ECU connector)

4. 4

   If wiring tests perfectly fine, verify if the ECU (A-095) has an internal hardware or software failure

1. 1

   Disconnect Power

   Turn off the key switch and disconnect the battery negative cable to prevent electrical damage.

2. 2

   Isolate the Circuit

   Disconnect the main engine harness connectors from the ECU.

3. 3

   Test for Shorts

   Probe the UB2 supply pins (2.08, 4.03, 4.19) on the harness side. Check for continuity to any constant 12V/24V power source.

4. 4

   Trace and Repair

   If a short to battery is found, trace the wiring harness to locate the damaged section. Repair the broken/melted wire insulation or replace the affected harness section.

5. 5

   Check Actuators

   Disconnect the actuators powered by the UB2 circuit to ensure one of the components hasn't failed internally and shorted the circuit.

6. 6

   ECU Replacement (if necessary)

   If the harness and actuators test completely normal and the short is isolated to the module itself, the ECU has suffered an internal failure and must be replaced or reprogrammed.

7. 7

   Reassembly and Clearing

   Reconnect all harnesses and battery cables. Use the Case IH Electronic Service Tool (EST) to clear DTC 667D / 3878 and run the engine to verify the repair.