Case IH 3591 – Engine Control Unit (ECU) / Electronic Diesel Control (EDC): SCR Catalyst Thermal Ageing Limit exceeded - Main Catalyst Efficiency Below Threshold

The Engine Control Unit (ECU) has calculated that the Selective Catalytic Reduction (SCR) catalyst has reached the end of its service life expectancy, or the downstream and upstream temperature/NOx sensors are reporting that the catalyst is no longer efficiently reducing emissions below the required threshold.

• Magnum series tractors
• Puma series tractors
• Steiger series tractors
• Patriot sprayers
• 621F wheel loader
• 721F wheel loader
• 821F wheel loader
• 921F wheel loader

1. 1

   Check for other active faults: Verify there are no active codes for DEF/Urea quality (e.g., code 3593 'Poor Reagent Quality') or dosing system issues, as poor DEF fluid will cause the catalyst efficiency to drop and trigger this code.

2. 2

   Visual Inspection: Check the SCR muffler assembly for physical damage. Ensure the exhaust gas piping is mounted correctly and has no exhaust leaks.

3. 3

   Sensor Verification: Ensure the upstream and downstream exhaust temperature sensors and NOx sensors are installed correctly.

4. 4

   EST Monitoring: Use the Case IH Electronic Service Tool (EST) to check the temperature sensors for accuracy. A skewed temperature sensor can cause the ECU to falsely calculate thermal ageing.

1. 1

   Verify sensor data

   Connect the Electronic Service Tool (EST) and verify the sensor data. If a temperature or NOx sensor is reading out of range, replace the faulty sensor, clear the codes, and retest.

2. 2

   Determine if SCR catalyst replacement is needed

   If the sensors are accurate, the DEF fluid is good, and the exhaust system is intact, the SCR catalyst has genuinely exceeded its thermal life limit and must be replaced.

3. 3

   Disconnect battery and cool exhaust

   Disconnect the machine's battery and allow the exhaust system to cool completely.

4. 4

   Disconnect wiring harnesses

   Disconnect the wiring harnesses for the NOx and temperature sensors from the SCR muffler assembly.

5. 5

   Unbolt exhaust piping and brackets

   Unbolt the exhaust piping clamps and mounting brackets securing the SCR catalyst/muffler.

6. 6

   Replace SCR catalyst

   Remove the old SCR catalyst and install the new unit. Ensure all gaskets and V-band clamps are properly seated to prevent exhaust leaks.

7. 7

   Reinstall sensors and reconnect wiring

   Reinstall the sensors (or install new ones if required by the service manual) and reconnect the wiring harnesses.

8. 8

   Reconnect battery

   Reconnect the battery.

9. 9

   Perform ECU reset

   ECU Reset (Critical): Connect the EST and perform the SCR catalyst replacement reset procedure. You must reset the thermal ageing limit/factor in the ECU so it registers that a new catalyst has been installed; otherwise, the fault code will remain active.