Proper management of a truck’s diesel particulate filter (DPF) system requires an understanding of how the truck’s specific system works as well as what maintenance is needed and when. In the event that something goes awry, it’s also nice to have a fully functional diagnostic tool that can help solve a range of problems.

“The DPF has always been the bane of my existence,” says Chris Freeman, director of sales/training HD at Autel, a developer of intelligent diagnostics, detection, and analysis systems. “I can honestly say that 90 percent of the problems trucks see these days are DPF-related.”

A common issue modern trucks face is the DPF becoming clogged.

“The DPF will not work properly if it gets clogged, and then the aftertreatment system will cause power issues,” says Bruno Gattamorta, vice president of sales and marketing for Cojali USA, a manufacturer of technology and diagnostic tools. “There are five stages of aftertreatment issues, ranging from a lax warning light to the vehicle being placed into limp mode.”

To prevent an issue from escalating, regimented preventive maintenance is key.

“Regular maintenance is important to remove ash that builds up within the DPF before it becomes clogged, which can create high back pressure and more frequent regenerations,” says Bruce Balfour of Clean Diesel Specialists Inc. (CDS), an integrated data-logging, installation, retrofitting, cleaning, parts distribution, and compliance center. CDS is a longtime Cojali customer.

As Autel’s Freeman explains, a DPF system uses a series of regenerations (regens) to burn off ash. But if the system’s sensor says there is too much NOx in the system, it will force diesel exhaust fluid (DEF) into the system to help burn off the NOx. Sensors and DEF make what sounded like simple filter maintenance much more complex.

Freeman says another challenge for technicians is a lack of standardization in the industry. Some DPF systems, for example, include selective catalytic reduction (SCR) while others do not. Some have SCR but lack a DPF. Some systems have sensors on the DPF, but not on the SCR, or vice versa. Technicians often require a good all-makes diagnostic tool that will help them stay on top of this wide range of potential DPF-related issues.

What core functionality should a diagnostic tool have?

First and foremost, fleets need a diagnostic tool that is capable of executing the necessary DPF cleaning procedures. Fleets can’t always count on running regens. Forced (manual) regens often become necessary.

“Some fleets have to set up a schedule for performing manual regens, whether that is once a week or whatever,” Freeman says.

A good example is a fleet running city routes where vehicles rarely get up to the necessary exhaust temperature for a running regen to kick in.

For fleets looking to do a fair amount of forced regens, an all-makes aftermarket diagnostic tool makes sense. For example, Cojali’s Jaltest, an all makes diagnostics tool, allows a technician to launch a forced regen, reset the filter, and monitor all of the relevant measurements to ensure that the process is working adequately.

In addition to forced regens, CDS’ Balfour says any good diagnostic tool should do the following:

• Scan, read, and clear codes of the aftertreatment module and engine control module
• Conduct hydrocarbon 7th injector and DEF injector testing
• Run all tests for OE-specific aftertreatment systems (i.e. SCR efficiency, DOC efficiency, DPF efficiency, NOx sensor)
• Reset the ash counter, maintenance intervals, and filter replacement serial number coding 

Fixing the DPF via a regen is not always the solution. Sometimes the filter needs to be taken out of the truck and cleaned in order to remove an adequate amount of ash. Other times, the filter needs to be replaced. In either event, there must be a communication to the ECM that everything is ready to go with the DPF. This is the DPF reset function which Balfour referenced above.

“A lot of aftermarket diagnostic tools do not have this reset functionality,” Autel’s Freeman points out. “When shopping for software, make sure it will be able to perform these reset functions. It’s literally a five-minute process most of the time. But if you don’t have the functionality on your scan tool, that could turn into a very expensive three-day process where you may even need to call in help from a dealer.”

Beyond the filter

Filter maintenance represents just one step in the DPF system. In some instances, solving a DPF-related problem involves pinpointing where the problem originated in the first place. That is why Freeman says it’s important to consider the entire DPF system when seeking out diagnostic tool functionality.

For example, a tool should be able to address DEF performance.

“You want to be able to conduct a variety of tests including DEF pump tests, purge tests, DEF injector tests, tank heater testes, pipe heater tests, and others,” Freeman explains.

“A lot of times, DPF system issues trace back to the DEF,” Freeman continues. “I had a customer who wasn’t getting any DEF into the exhaust. After testing, we’d identified a problem with the DEF doser block. The customer originally thought it was an injector problem. We ran a test and ruled that out. The faulty doser valve needed to be replaced … which wasn’t great news, but we pinpointed the problem in a short amount of time which was most important.”

Another fleet using an Autel diagnostic tool had an issue with an engine going into air-intake derate mode when the vehicle was driven above 50 percent throttle. The technician discovered similar pressure levels on both sides of the turbocharger, which is odd because there should never be as much pressure on the exhaust side. On this particular truck, there were monitoring sensors on the DPF, but not the SCR. The DPF itself had imploded, sending debris in the DPF housing and SCR. That congestion caused additional pressure to build up and begin bleeding over to the exhaust side of the turbo. Because there were no sensors on the SCR, the ECM could not detect this problem.

“The technician was able to use our diagnostic tool to check pressure levels on both sides of the turbo,” Freeman says. “The technician was also able to connect a four-channel scope to the tool and read signals going into each of the sensors to verify the data. Essentially, this helped the technician avoid needlessly changing out a sensor, which would have cost money but not solved the problem.”

In the case above, no fault codes were triggered; the vehicle was just sent into derate mode. In most DPF-related instances, however, a fault code is triggered. In fact, several codes are sometimes triggered. A good diagnostic tool will help technicians analyze these “cascading codes” so they can determine how they are related, which occurred first, and how to go about pinpointing the actual problem that needs to be resolved.