What Is Code SPN 3223 FMI 7? (Freightliner Cascadia Guide)

One of the things about these SPN codes is that there are far more than most people will count. Most people will give up once they reach one hundred but that is not even the tip of the iceberg when it comes to SPN fault codes. You won’t exhaust the supply at any time in your life.

This SPN code stands for “NOx Inlet Sensor failure to activate”. it can also stand for “NOx RAW Sensor Not Ready After Dewpoint Enable Check” Either way you will end up replacing the NOx sensor and maybe both of them.

To learn more about this code and what it means just continue to read our article. It explores the topic so you have the best information available to handle the repair quickly and easily. It is also not a tough fix to solve.

What is SPN 3223 FMI 7?


This code is telling you the NOx Inlet Sensor failure to activate message. What that means is that you most likely have a problem with one or both of the NOx sensors in your exhaust system.

As usual, the standard first step is to hook up the DiagnosticLink and see if there are other codes triggered at the same time. If there are, then you need to resolve and clear those codes first before tackling this simple problem.

We say simple simply because there are only 5 steps you need to take before this problem should be resolved. Should be is the operative word as not all repairs remain simple once you start on them.

Once those other codes are resolved, you will need to disconnect the SCR Inlet NOx sensor harness connector. Then check the wires and connectors for signs of damage, corrosion, signs of moisture, or other problems that would interfere with communications in this system.

If you find any damage, then make repairs to those components. However, if you don’t find any damage, then you need to replace the SCR inlet NOX sensor. The last step is the most important and it goes like this:

Drive vehicle for ten minutes after AS105: NOx Sensor Dewpoint enabled Inlet parameter changes state from zero to one and fault code goes inactive. Does AS105: NOx Sensor Dewpoint enabled Inlet parameter change state from zero to one and fault code stay inactive?”

If the fault code stays inactive, then clear all codes and release the vehicle. But if it is still active, you will have to replace theAftertreatment Control Module (ACM) and verify the repair.

SPN 3223 FMI 7 Freightliner Cascadia


We have seemed to jump the gun again and have given you all the information you need to know about this brand of the engine in the previous section. The repair process is the same as stated above and as we said earlier, this is not a complicated repair.

It will just take a little time to get to the heart of the problem and replace the right part. The key would be to make sure you resolve any other code that appears with this one.

The one step we left out in the previous section is #4 and it goes like this - “Using DiagnosticLink, monitor parameter AS105: NOx Sensor Dewpoint enabled Inlet while performing verification drive.”

There is no yes or no option to this step. Just go immediately to step 5 which may be the most important step once you start repair work. The purpose of the NOx sensors is to monitor the nitrogen oxide levels.

The inlet sensor monitors those levels before they are treated and the outlet sensor monitors those levels after they are treated. This information is used by the ECM to determine how much DEF is needed to treat the nitrogen oxide and reduce the amount going into the atmosphere.

If you have the MIL warning light illuminated, you should not experience a shutdown but you may experience a slight derate if you do not take care of the problem as quickly as you can.

ATS Electric System Problem Detected SPN 3223

There is an electrical side to this component that may trigger the SPN 3223 fault code. There is a list of possible sources for the NOx sensor not activating and we already discussed the last two. Here is the list of possible sources:

1. Damaged pins

2. Bent pins

3. Spread pins

4. Corroded pins

5. Unseated pins

6. Damaged wire

7. Faulty SCR inlet NOx sensor

8. Faulty Aftertreatment Control Module (ACM)

The first 6 are all mentioned in step #2 of the repair steps mentioned earlier. You need to check for damage on all of these components to get the NOx sensor up and working again.

When you find the damaged parts, then repair them as needed. There are no special techniques or tools involved that we are aware of and none have been mentioned.

Once you have completed the repair you should do a parked regen to clear the fault codes and verify the repair. If no fault comes up, then the problem has been solved.

If you see the 520363 fault code along with the SPN 3223 FMI 7 code, then that means "Selective Catalyst Reduction Inlet NOx Sensor Circuit Failed Open.” What that stands for is that the sensor has failed completely and you need to replace it.

SPN 3223 Aftertreatment 1 Intake Gas Sensor Heater Control FMI 7


Here is what this code means: “Exhaust Emission Controller aftertreatent 1 intake gas sensor heater control mechanism system not responding or out of alignment.” That is a mouthful to say and to write.

What this means is that the “NOx Raw Sensor not ready after Dewpoint enable inspection”. In other words, the sensor failed to activate. The repair is also not that difficult and it goes like this:

Connect DiagnosticLink. Are there any other fault codes?

1. a Yes; Repair other fault codes first.

1. b No; Go to step 2.

2. Disconnect the Selective Catalytic Reduction (SCR) Inlet NOx sensor harness connector.

3. Inspect the SCR Inlet NOx sensor and harness connector for signs of damaged, bent, spread, corroded, or unseated

(pushed out) pins, signs of moisture in the connector, or wire damage near the connector. Are any signs of damage


3. a Yes; repair as necessary. Verify repair.

3. b No; replace the SCR Inlet NOx sensor. Refer to section "Removal of the GHG14 Selective Catalytic Reduction Inlet NOx Sensor".

It is the same basic repair you had to do for the same code but with different components. Go to step 5 above to get to the final step to fix this problem. The same code will require the same repair no matter the engine or component affected.

The information for the fix for this section was made into an image and you can read it at this link.

SPN 3223 FMI 5


Unfortunately, there is only one mention of this code in the resources we have available. But no repair information was given for it. Just for the other fault code SPN 3223 FMI 3. What The SPN 3223 FMI 5 code stands for is “about Lambda Sensor Heater Open Circuit: Lambda Sensor Heater Open Circuit; Lambda Sensor Heater Open Circuit.”

The only repair advice we have come across is to replace the O2 sensor. Once replaced you will have to calibrate the new sensor. This may be the same repair for SPPN 3223 FMI 3 which stands for:

O2 Sensor Heater Control Circuit (high Side), Short-circuit To Battery: Aftertreatment 1 Intake Gas Sensor Heater Control Voltage Above Normal, Or Shorted To High Source; Lambda Sensor Heating: Shortcut To Battery Highside Switch”

There is not much information available at this time and we suggest you talk to a qualified mechanic to get more details on this error code. You will need the service maxx or Neds software to do the recalibration and if you do not have that, you will need to go to a mechanic anyways.

The O2 sensor is a vital part that helps control EGR functions as well as other components' operations. It is a must-repair and not something you can let slide for a week or two.

One word about displaying fault codes.

This link has a good explanation of this topic and the first part goes like this: “The ability to display diagnostic trouble codes (DTC) is an optional feature.

The customer must order feature 16HKT IP CLUSTER DISPLAY On Board Diagnostics in Gauge Cluster in order to retrieve fault codes using the electronic gauge cluster (EGC). Otherwise, Diamond Logic Builder Software (DLB) must be used to retrieve fault codes. “

Some Final Words

Finding solutions for the different fault codes is not always easy. Some fault codes are more common than others and there is a wealth of information available.

Other times they are not common and nothing is available to help solve the problem. Fault codes help but not all the time.

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