Exhaust Aftertreatment: Function & Maintenance

By Keith Kramlich, National Product & Training Manager at Takeuchi US

Regen Error – Monitor display varies by TL & TB Models.

It happens far too often: the operator hears the alarm or sees a notification the machine needs to perform a regeneration (regen), and instead continues to go on about their day. The payoff for finishing a day’s work: potential damage to the aftertreatment system, turbo charger or engine.

Was it worth it? When the owner/operator receives a bill for thousands of dollars in diagnostic and repair costs, likely not.

This article will help explain the exhaust aftertreatment purpose and function as well as proper care and maintenance practices to ensure your machine stays operational and productive.

About Exhaust Aftertreatment

Owning a machine equipped with a Tier IV engine requires different maintenance practices than older generation engines. There are also different variations of aftertreatment systems depending on the engine’s horsepower (hp).

These different variations, include:

  • Diesel Particulate Filter (DPF), which includes a Diesel Oxidation Catalyst (DOC)
  • DOC
  • DOC plus Selective Catalyst Reduction (SCR)
  • DOC, DPF and SCR


A DPF filter traps particulate matter (PM), also referred to as soot. PM is responsible for the black color in diesel exhaust and is a result of incomplete combustion. The particulates are trapped in the DPF until the soot load is to a point where a regen is required.

The regen process will oxidize the PM to decrease the soot load. However, ash is left behind, which is not combustible and must be removed by having the DPF removed and professionally cleaned.

The ash comes from burned engine lubricants, so it is vital to use low ash engine oil. Additionally, most manufacturers recommend professionally cleaning the DPF once every 3,000 hours to remove the ash. Of course, this interval can increase depending on operator use, fuel and engine oil types used.


DOCs are used on engines over 25 hp. The DOC assists in the oxidation of PM. During regen, extra fuel is injected into the combustion chamber of the exhaust stroke to significantly increase the temperature of the DOC. Once a certain temperature is reached (typically 500 to 600 degrees C and hotter), the soot begins to burn.


Most manufacturers are required to utilize SCR and DEF systems on engines over 75 hp. This system injects DEF, also known as UREA, into a special catalyst. This converts nitrogen oxide (NOx) into nitrogen, water and small amounts of carbon dioxide. This process can reduce NOx levels up to 90 percent.

The advantages of this system are cleaner emissions. Disadvantages can be added expenses with higher engine and maintenance costs. And, unfortunately there is no avoiding this.

Technology Helping the Cause

Regen procedures can differ between manufacturers. In most cases, the machine’s information system will alert the operator when a regen is occurring or when the operator needs to perform a regen.

Fortunately, today with advanced electronics and engine monitoring systems, new engines are incredibly intelligent. These systems will detect when the soot level is increasing in the DPF and will make a decision on if it needs to run a regen or not.

For instance, Takeuchi has an auto-regen feature. In the event of an auto-regen, if the engine RPM, engine load, exhaust and engine temperatures are in the proper range, the engine will perform a regen while the machine is still operating to decrease the soot load.

Performing a Stationary Regen

If the parameters are incorrect, the machine will warn the operator the machine needs to be parked for a stationary regen. For this, the operator should do the following:

  • Park in a safe area
  • Idle the machine all the way down
  • Lift the safety bar
  • Ensure engine coolant temperature is at or above 65 degrees C
  • Push/hold the regen enable switch until the engine idles up

Once finished, the engine will automatically idle back down, the regen signal will no longer be present, and the operator can get back to work.

Failure to Run a Regen

What happens to the machine if the operator does not comply to the regen? In this case, the soot will continue to increase until a threshold is reached where the machine will start to de-rate. If continued, catastrophic engine damage can occur.

At the point of machine de-rate, an authorized dealer will need to use the engine diagnostic software to either clear the code and force a regen, or, in extreme cases, the DPF will need to be removed and professionally cleaned prior to clearing the code.

The good news: in nearly all cases, it can be fixed. However, engine damage can occur if multiple regens are forced in a short amount of time, or if the engine continues to operate with a plugged or highly restricted DPF.

By not having the DPF professionally cleaned, it will cause “hot spots” and result in premature failure of the DPF. During the regen process, some fuel ends up in the engine oil, which is normal. But performing multiple regens back-to-back will cause the engine oil to start becoming diluted with fuel, which can cause disastrous damage to the engine.

Maintenance: More Common Mistakes

We often see the same mistakes being committed during regen. For starters, make sure to use low ash oil (CJ4 or CK4 is required). By not using this oil, it causes increased ash accumulation resulting in premature maintenance. Additionally, use ultra-low sulfur diesel.

Other mistakes include:

  • As said, ignoring regen requests
  • Using low-quality DEF (can damage DEF injection system)
  • Accidentally pouring diesel fuel into the DEF system (damages the quality and pressure sensors in the DEF injection system, in addition to damaging the SCR. A mistake like this can cost upwards of $10,000)
  • Removing the DPF and blowing it out with an air hose (this is illegal as it blows all the pollutants caught by the DPF into the atmosphere. The DPF needs to be professionally cleaned)

Any ulterior cleaning method needs to be approved by the manufacturer. At Takeuchi, we only recommend the conventional method of “baking” the DPF in a specialized DPF regeneration oven. No other method of treating is recommended.

When it comes to machines, never put off tomorrow what should be done today. It never pays to.