Case IH F-4334-12 - ECU – Engine Control Unit (ECU): DEF/AdBlue pressure did not drop when system was evacuated

When the engine is shut down, the aftertreatment system enters a depressurization or evacuation phase. The system attempts to empty the DEF lines by running the DEF pump in reverse or opening the dosing valve to allow the fluid to drain back into the tank. If the DEF pressure does not drop below a specific threshold (e.g., 250 hPa within 40 seconds) during this phase, the system detects a blockage in the pressure route and logs this fault. This typically results in an engine derate.

• MAGNUM AFS Connect
• 240 Series Axial-Flow (7240, 8240, 9240)
• Steiger / Quadtrac (350, 400, 450, 500, 550, 600)
• Magnum (180, 200, 220, 240, 250, 340)
• Puma (150, 215)
• Farmall (110A, 120A, 130A, 140A)
• Maxxum (115)
• Patriot (2250, 3240, 3340)

1. 1

   Check for accompanying codes using a diagnostic tool (e.g., DEF pump motor faults, DEF pressure sensor voltage faults, or DEF tank level/temperature faults) and diagnose those first.

2. 2

   Inspect the DEF dosing unit, pump, and lines visually for physical damage, kinks, leaks, or heavy white crystallization.

3. 3

   Check the DEF fluid quality for contamination, such as diesel fuel or coolant intrusion, which can damage the pump and plug lines.

4. 4

   Verify the DEF pressure sensor voltage; it should read between 4.5V and 5.0V. If outside this range, check the wiring harness for a short to power or an open circuit.

5. 5

   Run an SCR quantity test or air pressure test via the diagnostic tool to observe if the pump can build and hold pressure, and to monitor the pressure drop when commanded to evacuate.

1. 1

   Power Down

   Turn off the ignition and allow the aftertreatment system to power down completely (wait at least 2 minutes before disconnecting any components).

2. 2

   Disconnect Lines

   Locate the DEF supply and return hoses at the dosing unit. Squeeze the locking tabs together and pull straight upward on the elbows to disconnect them. Cap all open fittings immediately to prevent contamination.

3. 3

   Inspect and Clean

   Check the inlet filter screens and the pressure limiting unit (PLU) for blockages, crystallized DEF, or oily liquid buildup. Clean the fittings and screens using warm water or compressed air. Note: Never cut or machine SCR components, and wear nitrile gloves as DEF is corrosive.

4. 4

   Clear the Lines

   Flush the DEF lines with warm water and blow them out with compressed air to ensure the pressure route is no longer plugged.

5. 5

   Replace Components

   If the dosing valve (injector) is permanently blocked with crystallized urea, or if the DEF pump fails to reverse/evacuate after the lines are cleared, replace the faulty component.

6. 6

   Reassembly

   Reconnect the DEF supply and return hoses, ensuring they click securely into place. Reconnect the dosing valve harness. Discard and replace any O-rings if fittings were fully disassembled.

7. 7

   Verification

   Clear the fault codes using the service tool. Start the engine, allow it to idle, and perform a manual depressurization test or shut the engine down to verify the DEF pressure drops successfully without logging the code.