How We Test DPF Flow Before and After Cleaning

If your DPF has been cleaned but the warning light keeps coming back, it might never have been properly tested. Many garages offer a “clean” without actually checking if the filter flows like it should. That’s why every DPF we clean — on-car or off-car — is tested with real equipment, and the results are shared with you.

Why Flow Testing Matters

A DPF might look clean on the outside, but inside it could still be full of compacted ash. If the filter’s flow is still restricted, the vehicle’s ECU will detect rising back-pressure and cancel regeneration. This causes limp mode, increased fuel use, and possible MOT failure.

Without testing, you have no idea if your clean worked. That’s where we come in.

Our Testing Equipment

We use calibrated pressure and flow tools designed specifically for DPF units. For off-car cleans, we test each filter before and after the flush to measure:

• Back-pressure resistance
• Flow rate under controlled pressure
• Soot and ash percentage reduction

We log this data and include a printed report in your return package or hand it over in person if you visit the garage.

Before and After Example

Here’s a typical result from one of our recent DPF cleans:

• Before Clean: 98% blocked, pressure 90 mbar at idle
• After Clean: 5% blocked, pressure 6 mbar at idle

These readings show that the filter was restored to factory flow levels — no guessing, no “seems better” guesswork.

What About On-Car Testing?

During an on-car clean, we use live data from the vehicle’s ECU. This includes:

• DPF pressure sensor readings
• Pre- and post-clean exhaust gas temperature
• Calculated soot load

We monitor these readings throughout the clean and ensure that pressure and soot values drop before signing off the job.

Will I Get a Copy of the Results?

Yes. Every job includes a paper or digital report showing the flow test outcome. You can keep this for service history or hand it to your local mechanic when reinstalling the DPF.

This also supports MOT retests or customer Warranty (Terms & Conditions apply) claims if needed — giving confidence that your filter is performing properly.

What If the Filter Fails the Test?

If your DPF fails pressure testing — due to melted internals, oil contamination, or physical damage — we’ll let you know before proceeding. There’s no charge if we can’t clean it. You can then decide whether to replace the unit or diagnose upstream engine issues first.

We’re fully transparent — no “half cleaned” jobs or spray-and-go methods.

Need a Tested DPF Clean?

If you want the job done right, with data to back it up, call 07827533529 or book your DPF clean here.

We’ll test, clean and confirm the job’s complete — and provide full flow readings with every clean.