2 1

On-car DPF Cleaning

Focus on DPF On-car cleaning




Diesel Particulate Filters (DPF) are now the new normal for Diesel vehicles, so no doubt your shop has had its fair share of DPF issues through the door by now.

In this article rather than harp on the theory of DPF’s, I want to share a real case study, along with some tips and ways to repair DPF systems.

Case Study

2015 LW Ford Focus 2.0 – 53,456km – Check Engine Light (CEL), DPF warning light on solid

P2463-00 | Diesel Particulate Filter – Soot Accumulation

P246B-00 | Vehicle Conditions Incorrect for Diesel Particulate Filter Regeneration.

P165B-07 | Grill Shutter A Performance /Stuck. Mechanical Failure

On our first test drive, the vehicle did have symptoms of a blocked DPF – sluggish performance and raised DPF differential pressure sensor readings.  Below I have plotted our DPF pressure sensor readings (in mbar) against some trusted maximum values taken from BMW service information that I use as a general guide on all DPF’s.


DPF Differential Pressure Readings

Our partially blocked DPF


BMW Maximum permissible for Active Regen (mbar)
Idle 22 3
2000rpm 283 150
Regeneration Danger (2000rpm) 300+


At first you may glance past the Active Grille Shutter related fault code and charge right to the DPF, but you remember that DPF faults are most often a symptom, not the root cause.  If you are currently saying, “Active Grille what?”, a great analysis of the system can be found at:


Operating the grille shutters – easiest option on this model is watching the full sweep they will do at engine start-up – we could see that some of the vanes would jam, while the motor could be heard still trying to move them.  Impact damage to the vanes from road debris was the cause.

As cited in the aforementioned research link, the Active Grille Shutters are required to be open during DPF regeneration to allow airflow over the DPF, avoiding this 600°C+ exhaust furnace from damaging itself and nearby components.  Since the shutter system was not operating correctly, the PCM would not dare attempt an Active Regeneration for fear it would not be able to open the shutters.  The customer swears the CEL didn’t come on individually, rather that the DPF light came on, and then the CEL as well shortly after, even though they had attempted a highway speed drive.  The fact a CEL wouldn’t come on for a shutter issue that will effect DPF regeneration may be poorly written Ford software strategy or an embarrassed customer stretching the truth, but it does give weight to scanning cars for fault during servicing.

With a new set of vanes fit, the Active Grille Shutter system was now operating correctly and we could turn our attention to the symptom – the blocked DPF.  This is a fairly low km car that had an obvious system fault, so it is reasonable to assume the majority of the blockage in the DPF is burnable soot, as opposed to non-burnable ash which will build up in the DPF over time and eventually require professional cleaning or replacement of the DPF.

Given the very large backpressure, close to 300mbar, a forced regeneration would not be advisable, and in this case it wasn’t even offered on the scantool.  Many manufacturers are actually now starting to take the forced regeneration option off the scantool as it is abused by many and when actuated carelessly will result in melted DPF’s.

Instead, we carried out an on-car chemical DPF clean.  Many additive suppliers now offer a kit specifically designed for cleaning of the DPF with very little disassembly required.  We were using a Powermaxx product from Bluechem Australia, with the main component being a supplied pressurised canister which foams the Powermaxx DPF Top Gun Cleaner solution, designed to be sprayed into any accessible exhaust port post turbo, pre DPF.

In this case, our Ford had a very easily accessible exhaust gas temp sensor pre DPF, so we removed the sensor and, following the supplied instructions, applied the pressurised chemical into the DPF over the course of approximately 10 minutes.  We have also had great success on other models carrying out the process by spraying into the pre DPF pressure sensor hose, when it is a more convenient access point.

A tray was set up behind the vehicle, catching the sooty foam that you will sometimes emit from the exhaust.

After the process, the DPF pressures were greatly reduced, with a maximum reading at 2000RPM of 7mbar.

The fault codes were able to be cleared and a test drive was taken to clear any remaining chemical from the exhaust, and give the vehicle the opportunity to carry out a regeneration if it desired.  As DPF pressures were already reduced so greatly, the vehicle was happy and did not attempt regeneration, there was no need for it to, the product had already broken down the soot effectively even before the test drive.

This on-car cleaning process has worked well for us on a range of vehicles, with most requiring it after a split induction hose has caused large blockage, such as the Holden Captiva which often arrives in reduced power (limp) mode, with a soot reading of 200% due to the common intake hose split underneath the battery.

These chemicals offer a cost-effective, safe way to restore DPF’s back to service, however there are certainly situations when it is not applicable, such as:

  • A vehicle with a high ash reading. Ash loading is a theoretical calculated number, as ash will build in the DPF during normal use, and cannot be burnt out.  Removal of ash requires off-car cleaning methods or replacement of the DPF.  Some manufacturers will bring on a warning and fault code once an ash limit has been reached, with many providing the number in their service information – eg. From Erwin, 2011 VW Amarok 2.0L, Limit for changing DPF = 175ml.
  • A vehicle with DPF blockage due to melting of the DPF substrate, often caused by a forced regeneration at excessive soot levels (often a result of tricks like bypassing built-in safety guards by deceiving the ECU by bleeding off some of the pressure in the differential pressure sensor hose so the ECU sees lower pressure and allows a forced regen).
  • DPF plausibility fault codes can be set due to a DPF that flows too well – by monitoring for at least some backpressure, or sometimes for temperature change across the DPF during regeneration, these codes stop people fitting a straight DPF delete pipe, but can also pick up faults like internally cracked DPF’s.