P229F Code 6.7 Cummins-Causes and Solutions

The code P229F indicates a problem or performance issue with the nitrogen oxide sensor. It has various causes, including an engine misfire or a misaligned NOx sensor. The code can also indicate a failing DEF injector or a soot build-up on the sensor.

The earlier symptoms of the code P229F include reduced performance and a check engine warning light illuminating. Other symptoms are the vehicle going to limp mode and reduced engine acceleration and power. Repairing and fixing the failing parts most of the time solves the problems.

In this guide, I will explain the reasons and solutions of the code.

Table: What Triggers Code P229F on Cummins 6.7 Engines

Code P229F On Cummins 6.7



Faulty NOx SensorRepair or replace the NOx sensor
Misfire in the engineRepair the failing parts causing a misfire
A Failing Def injectorClean the DEF injector or replace it with a new one
NOx Sensor out of rangeReconnect the sensor or replace it with a new one

P229F Code and Possible Solution Explanation

P229F Code

The following part explains the above causes of the Code P229F on Cummins engines and how I fix the error.

1. Failing NOx Sensor

Most diesel engines, including the Cummins 6.7L, have two NOx sensors. The sensors can fail or malfunction due to soot building up on the sensor or a damaged cable. When the sensor has a problem, it cannot regulate the emissions correctly and might trigger the P229F code.


Soaking the NOx sensor in a cleaning solvent, like a fuel injector cleaner, for 3 to 4 hours repairs it. Afterward, spray a carburetor or throttle cleaner on the sensor. (our pick: Gumout 510013 High Mileage Fuel Injector Cleaner)

However, if the damage is extensive, you might need to replace the sensor. A new sensor costs between $400 and $800, but buy one with a warranty. Also, replace the NOx sensors and modules together for proper calibrations.

2. Engine Misfire

While an engine misfire is a symptom of a failing NOx sensor, it can also be the cause. The misfire happens if any of its cylinders fail to produce power. It can be caused by a faulty part, like a spark plug or an oxygen sensor. (1)


Most times, replacing the faulty part fixes the problem with the NOx sensor. However, during the fault period, the sensor can contribute to more misfires and more damage by sending the wrong information.

If that’s the case, you might need to replace the sensor when replacing other parts.

3. Failing DEF Injector

A DEF injector and a diesel fuel injector add smidgins of diesel fuel to the exhaust of a catalyst. In the exhaust, it evaporates to form ammonia and Carbon dioxide to help reduce NOx in the air. Contaminated, it can fail and possibly trigger the code P229F on your vehicle.


One way of repairing a DEF injector is by performing the reductant injection quantity test. The test involves the injector spraying the diesel for two minutes straight, and after repeating this several times, it can unclog it.

Also, you can use a steam cleaner to clean the crystalized exhaust fluid or replace the injector.

4. The Upstream or Downstream NOx Sensors Have Drifted out of Range

The nitrogen oxide sensors on the after-treatment system can be out of range or malfunctioning. One of the two sensors can give a low voltage because of soot buildup causing issues. The sensor’s harness can also be opened or shorted, causing the DTC code.


Secure the sensors tightly on their respective positions on the system. Also, verify the connection between the NOx sensor and the sensor modules and correct any mistakes. Sometimes, you might have to replace the sensors to fix the problem completely.

What Are the Symptoms of The Issues Causing Code P229F

P229F code symptom

1. Reduced engine power

Since the code signifies a problem in the after-treatment system; it directly impacts the drive train. The engine underperforms and is unable to reach maximum RPMs.

2. The vehicle gets into limp mode

Like in many cars, the RAM 2500 trucks, vehicles that use Cummins 6.7L engine, get into limp mode to protect against damage. If it regularly gets to limp mode, it can signify a developing issue, like a failing NOx sensor.

3. Warning Lights

Like the check engine light, the warning lights notify the driver of a developing problem. Issues like engine misfires that cause the diagnostic trouble code are known to make the check engine light illuminate.

4. The vehicle’s overall performance reduces

Any vehicle with emission problems performs poorly. The engine often misfires, causing reduced acceleration and poor fuel economy. The malfunctioning parts increase because each failing part directly impacts the other.

Some of the above symptoms can have other causes and signify different problems. To know for sure, perform a diagnostic test which you can do, or get a professional to do it. Also, if you notice any of the above symptoms, it’s best to visit an auto repair shop as soon as possible.

Read More- 

  1. How to Solve P2459 Code 6.7 Cummins Issue
  2. What is the Meaning of P2262 Code In a 6.7 Cummins


How Long Does It Take to Diagnose Code P229F?

The code P229F can take between 45 minutes and one hour to diagnose. If you have a diagnostic system, like the OBD-II, you can perform the diagnostic at home.

Can You Drive Your Vehicle with the Code P229F?

Yes, you can drive your vehicle to a safe spot or a repair shop if there is one nearby. However, don’t drive too far and if possible, call a professional instead of risking further and costly damage.

Bottom Line

Like other diesel engines, the powerful 400-horsepower 6.7L Cummins turbo engine uses a NOx sensor on its after-treatment system. They help control emissions as per regulations by monitoring the exhaust gas concentration. If they fail, they trigger the diagnostic trouble code P229F.

The failure has many causes, as covered in the sections above, followed by their possible solutions. The symptoms can help determine the problems before the DTC code for earlier repair. However, My suggestion is; always perform tests before repairs because the NOx sensor can’t differentiate between NOx and ammonia.


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