Case IH F-4334-15 - ECU – Engine Control Unit (ECU): DEF/AdBlue over pressure failure

The DEF (Diesel Exhaust Fluid) pump is generating or detecting pressure higher than the expected normal operating range (typically around 5 bar / 72 psi), or the system is unable to relieve pressure back into the tank.

• MAGNUM AFS Connect
• 240 Series Axial-Flow Combines (7240, 8240, 9240)
• Magnum series tractors
• Steiger series tractors
• Austoft 9900 sugarcane harvesters

1. 1

   Verify that there was enough DEF in the tank when the failure occurred and that the fluid is not contaminated or frozen.

2. 2

   Check the DEF return line (running from the DEF pump back to the DEF tank) for any blockages, kinks, or frozen fluid.

3. 3

   Perform a pressure drop test using an Electronic Service Tool (EST) to command the system to 5 bar, then stop the pump to ensure pressure drops through the backflow line.

4. 4

   Inspect the WEMA unit for cracks at the top of the suction or return tubes.

5. 5

   Pressurize the system and perform a visual check for external leaks at fittings or the main filter.

1. 1

   Clear Blockages

   If the return line is blocked, clear the blockage or replace the return line hose.

2. 2

   Test the WEMA Unit

   If the WEMA unit is cracked or leaking internally, remove it from the DEF tank. Pressurize it slightly on a bench to check for hairline cracks. Replace the WEMA unit if damaged.

3. 3

   Re-evaluate the System

   After clearing lines or replacing the WEMA unit, clear the active codes and re-run the DEF system evaluation using the diagnostic tool.

4. 4

   Replace the DEF Pump

   If the return line is clear and the pump continues to overpressure and log DTC F-4334-15, the DEF pump (supply module) has failed internally and must be replaced.

5. 5

   System Maintenance

   Clean the DEF tank and change the DEF filters (main filter, inline filter, and nipple filters) whenever the DEF pump is replaced.

6. 6

   Prime and Flush

   Use the Electronic Service Tool (EST) to run a flushing routine for 5 minutes, followed by running the Urea Dosing System Test (UDST) multiple times to prime the system and verify the repair.