Case IH 3594 – Engine Control Module (ECM): Torque limitation due to selective catalytic neutralization (SCR)

This is a symptom/derate code indicating that the engine software has intentionally placed the machine into a power derate (limp mode) to protect the SCR catalyst or to comply with emissions regulations because the system has detected a malfunction in the Diesel Exhaust Fluid (DEF) / SCR system.

• Steiger
• Magnum
• Puma
• Maxxum
• Farmall
• Axial-Flow 5130
• Axial-Flow 7130
• Axial-Flow 7230
• Axial-Flow 8240
• Axial-Flow 9230
• Patriot 4430
• Patriot 4440

1. 1

   Check for accompanying codes using a diagnostic scanner (look for 19xxx series DEF dosing errors or 3xxx series codes like 3593, 3595, 3611, or 3612).

2. 2

   Inspect DEF fluid quality for cloudy fluid, sediment, or crystallization (bad/contaminated DEF is the most common cause).

3. 3

   Check DEF tank vent lines to ensure they are not blocked by crystallized DEF, which can create a vacuum and starve the pump.

4. 4

   Monitor DEF pump pressure on the suction line using a diagnostic tool (should hold steadily around 72 psi / 5 bar).

5. 5

   Check NOx sensor plausibility by turning the key on without starting the engine; inlet, outlet, and intake temperatures should be within a few degrees of each other.

1. 1

   Address the Root Cause

   Based on your diagnostic checks, perform the necessary physical repair. This usually involves draining/flushing contaminated DEF, replacing a clogged DEF filter, replacing a failed NOx sensor, or replacing the DEF dosing pump.

2. 2

   Reset the Derate

   Replacing the broken part will not automatically clear code 3594. You must connect a laptop with the Case IH Electronic Service Tool (EST) or an equivalent heavy-duty scanner (like Jaltest) to manually reset the SCR derate state.

3. 3

   Perform a System "Healing" / Regen Cycle

   Once the derate is cleared, run the machine under a heavy load (or perform a forced regeneration via the service tool) to get the exhaust temperatures over 425°F–450°F for at least 30 minutes. This allows the NOx sensors to read properly and the ECM to verify the SCR system is functioning.