The average, working diesel particulate filter (DPF) reduces air-polluting particulate matter emissions by 95%, improves a truck engine’s longevity and performance, and keeps drivers in compliance with federal law.
Without one, drivers can face fines, the impoundment of their vehicles, and even license suspension.
When they're functioning well, DPFs improve fuel efficiency in the long run. But dysfunctional DPFs are another story.
Low-functioning and broken filters dramatically reduce efficiency, damage other engine parts, emit foul odors, and, most dangerously, sharply increase the risk of engine fires. As a driver, it’s vital to stay alert to signs of DPF trouble.
In this guide, our heavy-duty vehicle experts here at Point Spring & Driveshaft Co. explain what warning signs to look out for. Then, professional technicians detail the most common DPF problems, how to solve them, and tactics to prevent frequent recurrence.
What Is a Diesel Particulate Filter?
A diesel particulate filter (DPF) is part of the engine’s exhaust system. It’s a cylindrical device with a sensor connected to the engine control unit (ECU). Its body sits between the sensor, turbocharger, and the NOx trap on one side, and the exhaust pipe on the other. It functions to collect solid soot particles from diesel exhaust.
DFP Parts & Components
A DPF is composed of five parts. These are:
The diesel oxidation catalyst (DOC)
This receives exhaust from the turbocharger through its inlet
The inlet incorporates an exhaust gas recirculation (EGR) valve
The venturi tube
This creates a low-pressure region to direct airflow
Mixer
This receives and blends exhaust, air, and diesel exhaust fluid (DEF) injected upstream
The multi-component filter substrate
Components include a ceramic "honeycomb-like" structure, soot particle traps, and, optionally, soot-oxidating coatings of platinum or ceria.
The outlet, which connects directly to the tailpipe
What Is a DPF Filter’s Purpose?
The purpose of a DPF is to limit air pollution. It traps particulate matter waste generated by a diesel engine, to prevent them from contributing to air pollution.
5 Common Issues With Diesel Particulate Filters (And How To Solve Them)
DPFs receive unfiltered exhaust, pumped in by the turbocharger. Though this is the DPF’s purpose, over time the accumulation of soot can cause clogs in the filter. The DPF can also accrue damage over time. Clogs and structural damage both cause DPF dysfunction.
Signs of Clogged or Damaged DPF Filter
Ideally, the "check engine" warning light will turn on if the engine's DPF becomes too clogged or dysfunctional. But even if it doesn't, it's wise to pay attention to other warning signs:
Fuel efficiency drops dramatically
Cabin begins to smell like diesel, or there's a strong odor throughout
Exhaust smoke volume increases, and smoke becomes darker
Drivers have trouble starting the engine
Often, a dysfunctional DPF has one of five problems.
DPF Components Are Defective or Clogged
All DPF components can become clogged with soot or damaged. The most common sources of clogs and dysfunction are:
EGR valve
Venturi tube
Mixer
Outlet (cooler)
Examine these parts for buildup or breakage first.
Incorrect Oil Type (Exacerbating Soot Buildup)
An engine with a DPF isn’t compatible with every type of oil. Vehicle manuals specify the necessary traits of compatible oils. In general, oils that limit soot buildup in DPFs include:
Low SAPS oil
Low Ash oil
ACEA C3 standard oil
Faulty or Damaged Fuel Injectors
A poorly functioning fuel injector doesn't spray fuel effectively. This causes inefficient burns that generate too much soot. It can also damage the DPF by overloading its components.
If a fuel injector is low quality or damaged, it must be replaced.
Dysfunctional Turbocharger
When a turbocharger is dysfunctional, it can alter the air-fuel ratio in a hazardous way.
If the turbocharger doesn’t heat to a high enough temperature, it can’t trigger DPF regeneration or burn off excess soot. This, in turn, increases backpressure and causes soot clogs.
Infrequent or Ineffective Regenerations
DPF filter regeneration is the process that clears out the filter substrate. Regeneration burns the soot at a high heat, transforming it into CO2. It can be passive, active, or forced.
Infrequent or ineffective regenerations allow soot to accumulate in the filter indefinitely, until it stops working. Different issues can prevent regeneration efficacy, including:
Air conditioning problems
Turbocharger trouble