Case IH 19532 (DTC 374A) - ECU – DCU or Engine ECU (EDC): DEF/AdBlue pressure did not drop when system was evacuated / Back flow line is clogged

When the machine is shut down, the DEF supply module's reversing valve activates to evacuate fluid and prevent freezing. If system pressure fails to drop during this cycle, it indicates a physical blockage in the lines, a clogged dosing valve, or a mechanical failure of the reversing valve inside the pump.

• MAXXUM T4E
• Magnum 235-340 (Series 4)
• Steiger 350-600
• 240 Series Axial-Flow Combines (7240, 8240, 9240)

1. 1

   Check the DEF pressure line hoses, backflow (return) line, and connectors for kinks, physical damage, or frozen fluid

2. 2

   Remove the DEF hoses to physically detect any blockages in the lines

3. 3

   Check the DEF dosing valve visually and by using the electronic Service Tool test function

4. 4

   Remove the DEF dosing valve and inspect the mounting boss condition for severe urea crystallization

5. 5

   Inspect the DEF tank vent filter and inline filters for severe dirt ingress that can clog the system

1. 1

   Wait for purge cycle

   Safely shut down the machine and wait for the DEF pump to complete its purge cycle (do not disconnect the battery until the pump stops running, which can take up to 90 seconds).

2. 2

   Clear backflow line

   Disconnect the DEF backflow (return) line that runs from the supply module to the DEF tank. Clear any blockages or crystallized urea from the line.

3. 3

   Inspect and clean dosing valve

   Remove the DEF dosing valve (injector) from the exhaust stream. Inspect the nozzle and the mounting boss for crystallization. Clean the components if blocked.

4. 4

   Clean filters

   Inspect and clean the DEF tank vent filter and the main DEF filter located inside the supply module.

5. 5

   Replace DEF supply module

   If all lines, filters, and the dosing valve are completely clear, the internal reversing valve inside the DEF supply module has likely failed mechanically. In this case, the DEF supply module (pump) must be replaced.

6. 6

   Test system

   Reconnect all lines, clear the fault codes using a diagnostic tool, and perform a system test to verify that the pressure drops correctly during the evacuation cycle.