John Deere 004364.01 – ECU: SCR After Treatment Not Working Properly

The catalytic converter efficiency of the Selective Catalytic Reduction (SCR) system is extremely low. The Engine Control Unit (ECU) triggers this diagnostic trouble code when the downstream NOx sensor detects excessively high levels of Nitrogen Oxide (NOx) at the outlet of the SCR system. This indicates that the after-treatment system is not effectively converting NOx into nitrogen and water, which can lead to non-compliance with emissions regulations and potential engine performance limitations. A common root cause for this fault is the use of low-quality or contaminated Diesel Exhaust Fluid (DEF).

• 5085E
• 5090E
• 5090EL
• 5100E
• 9470RT
• 9520RT
• 9570RT
• 5M Series
• 6M Series
• 6R Series
• 7R Series
• 8R Series

1. 1

   Inspect DEF quality using a refractometer (urea concentration should be 31.8% - 33.3%). Fluid should be clear, colorless, and lack a strong ammonia smell.

2. 2

   Verify upstream and downstream NOx sensor readings using a diagnostic tool to ensure accurate measurement.

3. 3

   Visually inspect the SCR catalyst for damage, blockages, or deposits, and check the DEF dosing injector for crystallization or clogging.

4. 4

   Check the DEF injection system by listening for the pump to prime and inspecting lines for leaks.

5. 5

   Inspect the wiring harness and connectors for the NOx sensors and DEF dosing unit for damage, corrosion, or loose connections.

1. 1

   Resolve DEF quality issues

   If DEF is contaminated or out of specification (poor DEF quality cause), drain the DEF tank, flush with distilled water if necessary, and refill with fresh, ISO-certified DEF.

2. 2

   Replace faulty NOx sensor

   If the downstream NOx sensor is faulty, allow the exhaust to cool completely, disconnect the electrical connector, and remove the sensor. If seized, use penetrating oil or cut the sensor to fit a standard socket. Clean the exhaust bung threads with an M20 x 1.5 tap, apply anti-seize to the new sensor, install, and reconnect.

3. 3

   Replace DEF dosing unit or injector

   If the DEF pump or injector is failing, relieve system pressure, disconnect electrical and fluid lines, remove mounting hardware, replace the faulty component, and securely reconnect all lines.

4. 4

   Replace SCR catalyst

   If the SCR catalyst is physically damaged or irreversibly blocked, remove heat shields and clamps to access and replace the entire catalyst assembly.

5. 5

   Reset the SCR system

   Perform a drive cycle under load for 20-45 minutes to allow the system to heat up and clear the code. If persistent, use John Deere Service Advisor to perform a 'Reset NOx Sensor Learned Values', 'SCR System Reset', or initiate a manual service regeneration.