Case IH 3440 – Engine Control Unit (ECU): Auxiliary power relay low side ECU driver circuit over temperature failure

The Engine Control Unit (ECU) controls the voltage to the auxiliary power relay (K-064). The ECU actively monitors the K-064 low-side circuit for an over-temperature or over-current condition. If the ECU detects that the temperature or current on this low-side circuit has exceeded safe operating parameters, it will log fault code 3440.

• Puma Series Tractors
• 240 Series Axial-Flow Combines

1. 1

   Check for active faults and resolve any other codes before diagnosing 3440

2. 2

   Ensure the machine battery is not connected to an external power supply (jump box, external battery charger, or booster), as this can artificially trigger the fault

3. 3

   Visually inspect the relevant harnesses and connectors for damage, bent or dislocated pins, corroded terminals, or broken wires, and verify all connectors are fully seated

1. 1

   Turn the ignition switch to the OFF position.

2. 2

   Disconnect connector X-911 from the ECU (A-095).

3. 3

   Using a multimeter, perform a continuity check on the low-side control circuit.

   Measure from X-911 pin 45, wire 646 (Blue) to X-037 pin R2_85, wire 646 (Blue).

4. 4

   If there is NO continuity, locate the break in the wiring harness and repair the broken conductor.

   This indicates an open circuit condition in the K-064 low-side control circuit.

5. 5

   If there IS continuity, check the ECU (A-095) for the appropriate software version and re-flash the ECU with the latest software if necessary.

   This indicates the wiring is intact.

6. 6

   Perform a wiggle test by flexing the involved harnesses to reveal any intermittent breaks or shorts in the wiring while operating the machine and monitoring the display.

7. 7

   Once the damaged wire is repaired or the ECU is re-flashed, clear the fault code and operate the machine to verify the repair.