John Deere 3226 – ECM: Outlet NOx Sensor Abnormal Reading

Fault code 3226 indicates an abnormal reading from the Aftertreatment 1 Outlet NOx sensor, located downstream of the Selective Catalytic Reduction (SCR) catalyst. The Engine Control Module (ECM) uses this sensor to measure nitrogen oxide levels and verify the efficiency of the emissions aftertreatment system. An abnormal reading can result from a failed sensor, exhaust leaks introducing oxygen, wiring harness issues, or poor DEF quality reducing SCR efficiency.

• 6R
• 7R
• 8R
• 8RT
• 9R
• 9RT
• 9RX
• S660
• S670
• S780
• R4030
• R4038
• R4045

1. 1

   Retrieve all fault codes using a diagnostic tool to check for related issues, such as inlet NOx sensor faults (SPN 3216).

2. 2

   Inspect the exhaust system for leaks, cracks, or damage near the NOx sensor mounting location.

3. 3

   Examine the NOx sensor wiring harness and connectors for chafing, heat damage, corrosion, or bent/spread pins.

4. 4

   Test DEF quality using a refractometer (urea concentration should be approximately 32.5%).

5. 5

   Inspect the DEF dosing valve for crystallization buildup that could restrict DEF flow.

6. 6

   With ignition on and engine off, measure voltage at the harness side of the NOx sensor connector (typically 11.5 to 12 volts).

7. 7

   Verify a good ground connection at the sensor connector and check harness continuity to the ECM.

1. 1

   Prepare machine

   Ensure the engine is off and the exhaust system has completely cooled down. Disconnect the negative battery cable to prevent electrical hazards.

2. 2

   Locate and disconnect sensor

   Locate the outlet NOx sensor in the exhaust pipe after the SCR catalyst. Carefully disconnect the electrical connector from the NOx sensor module.

3. 3

   Remove faulty sensor

   Using a 22mm wrench or specialized NOx sensor socket, carefully unscrew the sensor from the exhaust pipe.

4. 4

   Clean exhaust threads

   Clean the threads in the exhaust pipe bung using an M20 x 1.5 thread chaser to ensure proper installation of the new sensor.

5. 5

   Install new sensor

   Screw the new NOx sensor into the exhaust pipe and tighten to 40-50 Nm. Ensure anti-seize compound is applied to the threads (many new sensors come with this pre-applied).

6. 6

   Secure wiring

   Reconnect the electrical connector to the new sensor module. Secure the wiring harness away from heat sources and sharp edges using zip ties.

7. 7

   Clear codes and reset

   Reconnect the battery cable. Clear all fault codes using a diagnostic tool. Perform a system reset or a forced regeneration cycle if required for the ECM to recognize the new sensor.