A blocked diesel particulate filter (DPF) is one of the most common issues diesel mechanics deal with. Most modern diesel vehicles will attempt a passive or active regeneration on their own while driving, but when that fails, you need to force one manually using a scan tool. Here is what the process looks like, what can go wrong, and what tool you need to do it properly.

Quick recap: what is a DPF and why does it block?

The DPF is a filter in the exhaust system that captures soot particles from diesel combustion. Over time, it fills up with soot and needs to be cleaned out by burning the soot off at high temperatures. This is called regeneration.

Passive regeneration happens automatically during highway driving when exhaust temperatures are high enough. Active regeneration is triggered by the ECU when the DPF reaches a certain soot load, using post-injection fuel to raise exhaust temperatures. Both happen without driver involvement.

The problem is that many diesel vehicles in Australia spend a lot of time on short urban trips or stop-start driving where exhaust temperatures never get high enough to regenerate properly. The DPF fills up, the vehicle goes into limp mode or throws a DPF warning, and you need to intervene.

What is a forced DPF regeneration?

A forced DPF regen (also called a stationary regen or service regen) is a manually triggered regeneration process initiated through a scan tool. Rather than waiting for the right driving conditions, you command the vehicle's ECU to start the regeneration cycle immediately while the vehicle is stationary.

The process raises exhaust temperatures to around 550 to 650 degrees Celsius, burning off the accumulated soot. A full cycle typically takes 20 to 40 minutes.

Before you start: check these things first

Not every blocked DPF situation calls for a forced regen. Before connecting the scan tool, check:

• The DPF soot load percentage. Most scan tools will show this as a live data value. If it is above 80 to 90%, a forced regen may work. If it is at 100% or near it, a regen may not succeed and the DPF may need to be removed and cleaned or replaced.
• Whether there are any related fault codes preventing regeneration. A faulty DPF pressure differential sensor, a failed temperature sensor, or an EGR fault can all block the regen from starting. Fix these first.
• Engine oil level and condition. Diesel engines use post-injection to raise DPF temperatures, which can push unburnt fuel into the oil. If the oil is already contaminated, it needs to be changed before and after a forced regen.
• Coolant temperature. The engine needs to be at full operating temperature before a forced regen will initiate.

The forced regen process

Step 1 — Connect and identify the vehicle

Connect your scan tool to the OBD2 port with the ignition on. Select the vehicle and navigate to the engine ECU or exhaust aftertreatment system.

Step 2 — Check live data

Before initiating the regen, check the DPF soot load, DPF pressure differential, and exhaust temperature values. Confirm the engine is at operating temperature and there are no blocking fault codes.

Step 3 — Start the forced regen

Navigate to Special Functions or Service Functions and select DPF Regeneration or Diesel Particulate Filter Regen. The scan tool will typically display a checklist of pre-conditions. If everything is met, you can start the process.

The vehicle will need to be in park or neutral with the handbrake on. Do not attempt this inside a building. The exhaust temperatures are very high and the exhaust output is significant. Do this in an open area or with the exhaust vented outside.

Step 4 — Monitor the process

Keep an eye on the DPF soot load and temperature values as the regen runs. Most scan tools will show these in real time. The process should bring the soot load progressively down. A normal cycle takes 20 to 40 minutes.

Do not switch off the ignition or disconnect the scan tool while the regen is running.

Step 5 — Confirm completion

Once the regen is complete, the scan tool will indicate success and the DPF soot load should be significantly reduced, ideally below 20%. Clear any DPF-related fault codes and test drive the vehicle to confirm normal operation. Not every model of car will let you know the DPF regen is complete but if the RPM drops back to normal you can check your live data to confirm.

What if the regen fails or will not start?

If the scan tool will not initiate the regen, or the regen fails partway through, the most common causes are:

• A fault code blocking the process that has not been cleared
• The DPF soot load is too high for a regen to succeed (usually above 90 to 95%)
• A faulty DPF pressure sensor giving incorrect readings
• An EGR system fault preventing proper exhaust management
• Low fuel (the post-injection process uses fuel rapidly)

If the soot load is at 100% and the regen will not complete, the DPF typically needs to be removed for a chemical clean or replacement.

Sometimes you can trick the ECU into thinking you have replaced the DPF by doing a DPF data reset or replacement if thats an option for that vehicle. Then re-attempt the DPF burn.

Which scan tools support forced DPF regen?

You need a scan tool with DPF regeneration in its special functions menu. From our range, the following all support DPF regen on supported vehicles:

• Autel MK808K-BT
• Autel MS906 Pro
• Autel MaxiCheck MX900
• Autel MaxiCOM MK900
• Launch X431 ProS V5.0
• Launch X431 ProS Elite
• Topdon TopScan Pro
• Topdon ArtiDiag900BT

Coverage varies by vehicle brand and model.

Can you do a DPF regen without a scan tool?

Technically, you can attempt to trigger a passive or active regen by doing a long highway drive at sustained RPM. Some diesel owners have success with this for lightly blocked DPFs. But for a heavily soot-loaded DPF where the vehicle is in limp mode, a scan tool is the only reliable option for a stationary forced regen.

Bottom line

Forced DPF regen is a routine service function for any workshop handling modern diesel vehicles. Having a scan tool that supports it means you can handle DPF issues in-house rather than referring them to a dealer or specialist. For the volume of diesel vehicles on Australian roads, it is a function that will pay for itself quickly.

Need help choosing a scan tool with DPF regen support for your vehicle range? Browse our range or contact our Australian support team.