Diesel Engine DPF Filters Explained

Diesel Particulate Filters (DPFs) are one of the major additions to exhaust systems in recent years. DPFs are designed to clean exhaust and eliminate soot, carbon, and that characteristic diesel smell. Downstream from the DPF is the VGT turbo, which relies on its strong airflow to drive the turbine. 

Like any EGR system component, regular maintenance is key in keeping your DPF in service. To ensure your VGT Turbo and your diesel engine as a whole are running as they should, we're taking you through the things you should keep an eye out for!

You can also watch our video for more information:



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The Introduction of the DPF

When the DPF first came out, there were a number of challenges that arose. As with any new technology, they weren't always perfect out of the box and we saw a tremendous amount of DPFs that would crack, fail, or break.

This caused a big issue, because at that point they were either out of warranty and manufacturers wouldn't stand behind them, or, if they weren't used or maintained properly, they didn't qualify for a warranty.

So, essentially, they were expensive and they weren't very durable or reliable. If they failed, operators were then faced with two options: putting a $3,000-7,000 DPF on, or just putting a pipe on and eliminating it. In the end, you would see people deleting them, and that was probably the start of our experience with DPFs. They just weren't made as well as they are today.


Symptoms of Diesel Engine DPF Failure

Like most other failures in your diesel engine, there are a few key symptoms you can watch out for to let you know if you have a failing DPF filter. Here are four symptoms to look for if your DPF is in need of service:

  • DPF Differential Pressure Sensor Alert will appear on the dashboard, alerting you that the DPF is plugged.
  • Cracks can appear on the DPF filter, which can also cause black smoke to emit from the tailpipes. 
  • Soot might appear in the tailpipe. The DPF may be damaged internally, allowing soot to pass through the filter and out of your tailpipe. 
  • Your VGT turbo isn't spooling properly.

Want to know more about VGTs? Read our VGT Turbocharger Failure Diagnosis!

How are These Problems Related to Your DPF Filter?

In most cases, a DPF filter problem is the result of another failed engine component that hasn't been diagnosed. Upstream failures can lead to excess carbon and soot production. Injectors not firing properly or timing issues are both common factors that lead to DPF plugging. 


failing dpf filter injector problems | Highway & Heavy Parts


If your injectors are worn and you're not spraying fuel in at the right pressure, then the atomization is not proper and the fuel to air ratio isn't right. Then, it doesn't burn as clean as it should and we start to see more particulate matter generated, which begins to plug the filter. Once this starts to plug, it has a cascade effect. The plug builds up faster and faster, because the problem is multiplied.

Bore polishing can also lead to DPF failures. If the engine does not have APR rings installed and carbon builds up on the top and side of the piston, the temperature will not be correct and it won't burn correctly. 

When the DPF light shows up on the dashboard, drivers are faced with forced regenerations that take them off of the road. Ignoring the problem leads to a complete failure of the filter. As we mentioned earlier, this has caused OEMs to void the warranties because of little or no maintenance on the filter. Then you're faced with that $3,000-7,000 replacement bill for a new DPF.


failing dpf vgt turbo problems | Highway & Heavy Parts


Similarly, VGT turbos can be damaged from a failing DPF.  The turbine wheel on the exhaust side of the VGT is downstream from the DPF and is driven by forced exhaust gases.  In the event that the DPF gets plugged and airflow is reduced or blocked, the turbine wheel will not be able to spool up properly.  The compressor wheel on the cold side is also affected by the slow turbine speed, not being able to bring in enough cold air for combustion.  The result is your VGT not performing at optimal specs.


What Can You Do To Keep Your DPF Operating Properly?

The best way to prevent DPF filter issues in your diesel engine is to do regular maintenance on it. Make sure that you're cleaning your DPF filter to help prevent buildup and clogs. 

To properly clean the DPF, it must be removed from the vehicle and put through a special cleaning process. Regens alone will not do the job. DPF filters should be cleaned every 6 months to maintain proper performance.

Learn what other engine maintenance you should perform regularly in our blog about preventive maintenance!


Even though it's not a part you probably think about often, your DPF filter can have a huge impact on the overall function of your diesel engine. Keep yours running great and let HHP help you with any problems you might have!


Need help with your DPF or any other diesel engine part? Call our ASE Certified Techs at 844-304-7688, or, you can always request a quote online!