Case IH 3399 – Engine Controller (ENG / ECU / EDC): Engine Fuel Lift Pump relay driver over current fault

The control module has detected an electrical current draw on the fuel lift pump relay driver circuit that exceeds the maximum allowable threshold. This is typically caused by a short circuit to ground in the wiring harness, a shorted relay coil, or a failing electric fuel lift pump drawing excessive amperage.

• Steiger T4B
• Magnum 225
• Magnum 235
• Magnum 240
• Magnum 250
• Magnum 260
• Magnum 280
• Magnum 290
• Magnum 310
• Magnum 315
• Magnum 340
• Magnum 370
• Magnum 380

1. 1

   Relay Inspection: Locate the fuel lift pump relay in the fuse/relay distribution panel. Check for melted plastic, burnt electrical smells, or corrosion on the relay terminals.

2. 2

   Wiring Harness Check: Inspect the wiring harness between the Engine ECU and the fuel lift pump relay. Look for chafed wires, pinched harnesses, or exposed copper that could be shorting to the chassis (ground).

3. 3

   Component Current Draw: Test the fuel lift pump relay coil for an internal short. Additionally, check the electric fuel lift pump itself; a failing pump motor can draw excessive current.

4. 4

   ECU Pin Inspection: Disconnect the Engine ECU and check the specific pin for the lift pump relay driver for signs of arcing or heat damage.

1. 1

   Disconnect Power

   Turn off the machine and disconnect the negative battery cable to prevent electrical spikes.

2. 2

   Test/Replace the Relay

   Remove the fuel lift pump relay. Test it with a multimeter. If the internal coil resistance is out of spec or shorted, replace the relay.

3. 3

   Repair Wiring

   If the relay is good, trace the wire from the ECU to the relay block, and from the relay block to the lift pump. Repair any damaged sections of the wiring harness using proper solder and heat-shrink tubing.

4. 4

   Test/Replace the Lift Pump

   If the wiring and relay are intact, the electric fuel lift pump is likely failing internally and drawing too much amperage. Drain the fuel housing, disconnect the fuel lines and electrical connector, and replace the lift pump assembly.

5. 5

   Reassemble and Clear Codes

   Reinstall all components, reconnect the battery, and use a diagnostic service tool to clear the 3399 fault code from the Engine ECU.

6. 6

   Verify Repair

   Cycle the key to prime the fuel system, start the engine, and verify that the lift pump operates smoothly without triggering the fault code.