Case IH 17896 (F-4376-31) - ECU – Engine Control Module (ECM) / EDC17 or Dosing Control Unit (DCU): SCR reverting value failure predicted as SCR pressure did not reduce when reverting switched to backflow pipe at low voltage and low ambient temperature.

When shutting down the engine, the SCR system initiates a purge cycle. A reverting valve inside the DEF pump switches over to reverse the flow of DEF, pulling it out of the dosing module and lines and sending it back into the DEF tank via the backflow pipe to prevent freezing. This fault is triggered when the system attempts this purge cycle, but the DEF pressure sensor detects that the pressure did not drop as expected. This failure condition is specifically detected during a state of low system voltage and low ambient temperature.

• VESTRUM CVX
• Farmall 40
• Farmall 45
• Farmall 50
• Farmall 95A
• Farmall 100C
• Farmall 110C
• Maxxum 110
• Maxxum 115
• Maxxum 125
• Maxxum 140
• Magnum
• Puma
• Steiger
• Quadtrac
• Axial-Flow 5130
• Axial-Flow 7230
• Axial-Flow 8230
• Axial-Flow 9230
• Patriot
• Titan
• Farmlift

1. 1

   Check battery and charging system voltage, as low voltage can prevent the reverting valve or diaphragm pump from actuating properly during the key-off purge cycle.

2. 2

   Inspect the DEF supply module, dosing module, and all DEF lines (especially the white backflow line) for kinks, blockages, or frozen urea crystals.

3. 3

   Verify the engine coolant lines running to the DEF supply module are getting hot to ensure the internal heating plate is functioning.

4. 4

   Use a diagnostic scan tool to manually actuate the reverting valve and DEF pump, listening for clicks and monitoring pressure changes.

5. 5

   Verify the DEF pressure sensor is reading accurately and is not stuck at a high value when the system is off.

1. 1

   Resolve Voltage Issues

   If battery voltage is low, charge or replace the batteries and repair any charging system faults before proceeding with SCR repairs.

2. 2

   Thaw and Clear Lines

   If operating in freezing temperatures, bring the machine into a warm shop to thaw. Disconnect the DEF backflow line and blow low-pressure compressed air through it to ensure it is not clogged with crystallized DEF.

3. 3

   Clean or Replace DEF Filter

   Remove the main DEF filter cover on the supply module and replace the DEF pump filter element. Clean any dried white urea crust from the housing using distilled water only (do not use tap water or chemicals).

4. 4

   Replace the DEF Supply Module

   If the lines are clear, voltage is good, and the pressure still fails to reduce during the purge cycle due to a stuck reverting valve, the entire DEF Supply Module must be replaced.

5. 5

   Clear Codes and Test

   After replacing the module or clearing a blockage, use a diagnostic scan tool to clear the fault code. Run the engine to build SCR pressure (typically around 9 bar / 130 psi), then perform a normal key-off shutdown. Monitor the scan tool to ensure the purge cycle completes and pressure drops to zero.