John Deere 3216 – ECU: Inlet NOx Sensor Fault

Suspect Parameter Number (SPN) 3216 indicates a fault within the circuit or performance of the Aftertreatment 1 Inlet NOx Sensor. This sensor is located in the exhaust stream before the SCR catalyst and measures the concentration of nitrogen oxides (NOx) entering the aftertreatment system. The Engine Control Unit (ECU) uses this data to calculate the precise amount of Diesel Exhaust Fluid (DEF) needed to neutralize pollutants. A fault with this sensor can lead to incorrect DEF dosing, increased emissions, reduced fuel efficiency, and potential damage to other aftertreatment components. When active, the machine will typically display a check engine light and may enter a derated power state.

• 5100E

1. 1

   Scan for all active and stored fault codes using a diagnostic tool like John Deere Service ADVISOR, as other codes may point to a related issue causing the 3216 fault

2. 2

   Visually inspect the inlet NOx sensor's wiring harness for any signs of damage, such as melting, chafing, or breaks

3. 3

   Check the sensor connectors for corrosion (green rot), loose pins, or moisture intrusion

4. 4

   Verify that the NOx sensor is receiving the correct power and has a solid ground connection, which may involve checking relevant fuses in the power distribution center

5. 5

   Inspect the exhaust system for any leaks upstream of the inlet NOx sensor, as introduced oxygen can cause incorrect readings

6. 6

   Analyze live data from both the inlet and outlet NOx sensors using a scan tool. Run a forced DPF regeneration with the DEF injector disabled; readings should be nearly identical. A difference of over 50 ppm points to a faulty sensor

1. 1

   Disconnect the sensor

   Unplug the electrical connector from the NOx sensor control module. Depending on the machine, this may be located in a sensor box along with the outlet sensor module.

2. 2

   Remove the sensor probe

   Use a specialized cutaway socket (often 22mm or 7/8") to remove the sensor probe from the exhaust pipe bung. Be aware it may be seized.

3. 3

   Clean the threads

   Use a thread chaser or tap (typically M20x1.5) to remove any carbon buildup or corrosion from the exhaust bung threads to ensure the new sensor is not damaged during installation.

4. 4

   Install the new sensor

   Thread the new sensor probe into the exhaust bung, starting it by hand to prevent cross-threading. Tighten the sensor to the manufacturer's specified torque value.

5. 5

   Mount the control module and connect

   Secure the new sensor's control module and plug in the electrical connector.

6. 6

   Clear fault codes

   Use a diagnostic tool to clear the active fault codes from the ECU.

7. 7

   Verify the repair

   Operate the machine under normal conditions, bringing the exhaust system up to operating temperature to ensure the fault code does not return. A forced regeneration or specific system test may be required.