Deutz-Fahr SPN 3364 FMI 2 – ACM 2.1 / MCM2 / MCM2.1: NOx Sensor (Downstream SCR): Measured value out of tolerance

The downstream Nitrogen Oxide (NOx) sensor provides readings that are implausible or outside the expected parameters. This disrupts the exhaust gas cleaning process, often resulting in an illuminated AdBlue/Check Engine light, increased DEF (AdBlue) consumption, and engine derate (limp mode).

• 6105
• 6110
• 6120
• 6130
• 6140
• 6150
• 6160
• 6170
• 6180
• 6190
• 7200
• 7250
• 7300
• 7340
• 9300
• 9340
• 9370
• 9400

1. 1

   Inspect the wiring harness leading to the downstream NOx sensor for chafing, melting, or corrosion

2. 2

   Check the exhaust piping between the SCR catalyst and the downstream NOx sensor for exhaust leaks

3. 3

   Verify DEF (AdBlue) quality for contamination, dilution, or expiration

4. 4

   Check for upstream faults (e.g., active codes for the AdBlue dosing pump SPN 4334 or SCR temperature sensors SPN 3480)

1. 1

   Preparation

   Turn off the engine, disconnect the battery, and allow the exhaust system to cool completely.

2. 2

   Locate the Sensor

   Find the downstream NOx sensor on the exhaust tailpipe, located after the SCR catalyst.

3. 3

   Disconnect Electronics

   Carefully unplug the sensor's electrical connector from the machine's wiring harness.

4. 4

   Remove the Sensor

   Use a specialized NOx/O2 sensor socket (usually 22mm) to unscrew the sensor from the exhaust pipe.

5. 5

   Install the New Sensor

   Apply a small amount of anti-seize compound to the threads of the new sensor (if not pre-applied by the manufacturer), ensuring none gets on the sensor probe. Thread it in by hand to prevent cross-threading, then torque to OEM specifications. Ensure the sensor is installed at the correct angle (bosses directed upward) to prevent condensation from pooling on and destroying the sensor tip.

6. 6

   Reassembly

   Reconnect the electrical connector and secure the wiring harness away from extreme heat sources.

7. 7

   Clear Codes

   Reconnect the battery, connect a diagnostic tool, and clear the SPN 3364 FMI 2 fault code.

8. 8

   Validation

   Run the engine through a warm-up cycle or perform a forced SCR system test/regeneration via the diagnostic tool to verify the sensor is reading within tolerance.