How Our DPF Flow Test Proves the Job’s Done Right

You’ve paid for a DPF clean. The warning light’s off. But how do you know the filter’s actually clear and flowing like it should? That’s where our before-and-after DPF flow testing makes the difference.

Every DPF that comes through our workshop is tested both before and after cleaning. You get a printed report showing exactly how blocked it was and how well it’s flowing now — so you can see the results in black and white.

In this post, we explain how flow testing works, why it matters, and how it protects your engine and your wallet long after the cleaning is done.

What Is a DPF Flow Test?

Our flow test measures the resistance inside your diesel particulate filter. The more soot and ash packed into the core, the harder it is for exhaust gases to pass through. We use a specialist pressure-rig that forces air through the filter and records the flow rate.

The result is shown in millibar (mbar) pressure — a clean filter typically reads below 5 mbar. Blocked units can read 50, 70 or even 90+ mbar. Our test proves exactly where your filter stands.

What Happens During the Test?

• Step 1 – Visual Inspection: We check for cracks, melted cores, and oil contamination. No point testing if the DPF is physically damaged.
• Step 2 – Initial Flow Test: The filter is mounted to our calibrated airflow bench. We measure the back-pressure across the full unit and record the result.
• Step 3 – Cleaning Process: The DPF is flushed with detergent and heat, then air-blasted to remove all soot and ash.
• Step 4 – Final Flow Test: Once dry and cool, we test again. The result is logged and printed, showing a clear “before” and “after” value.

This report stays with the job and acts as proof that the cleaning has worked — ideal for garages, fleet operators, or drivers needing MOT confidence.

Why Flow Testing Matters

Not all DPF cleaning is equal. Some services just spray chemicals through the pipe and hope for the best. Without a flow test, you’re guessing whether the filter is really clean — or just temporarily cleared.

Our process gives you hard data:

• Confirms the blockage level before cleaning
• Proves restored performance after cleaning
• Builds trust with your garage or customers
• Supports Warranty (Terms & Conditions apply) claims or return-to-lease checks

If you’ve ever asked, “Is my DPF actually clean?” — the flow test is your answer.

On-Car Cleaning? Still Tested.

Even with our on-car DPF clean, we use live data to monitor back-pressure via the sensors. We compare readings before and after the flush and regen, so you see the pressure drop in real time.

We check soot load, regen history, and pressure readings at idle and under load. If the values don’t return to spec, we don’t sign the job off.

Off-Car? The Gold Standard.

Our off-car DPF clean gives you the most complete reset. The filter is removed, chemically soaked, flushed both ways, and fully dried. Only then do we test and record the final flow. If it passes, you get the printout with your filter. If it fails, we don’t charge — and we’ll explain your options.

What the Numbers Mean

These values help you and your mechanic decide whether to refit the filter, run a regen, or investigate upstream issues like injectors or oil consumption.

What If My Filter Fails the Test?

If your DPF has melted, collapsed internally, or been filled with engine oil, no amount of cleaning will restore proper flow. In those cases, we stop the process and contact you before going any further. We’ll explain the issue and help you source a replacement if needed.

Our terms and conditions explain when a Warranty (Terms & Conditions apply) applies and what causes might void the guarantee (Terms & Conditions Apply) — including underlying faults like turbo seals or bad injectors.

When You Might Need a Flow Test

• After the DPF warning light returns shortly after cleaning
• When buying a used DPF or suspecting a cheap clean
• To prove the DPF is working before MOT
• To show your customer or leasing company that work was done properly

Included With Every Job

At DPF Clean, we don’t charge extra for testing. It’s part of the process — and the only way we can stand behind our work. You get the data, the results, and the peace of mind.

We also back every job with a 6-month flow guarantee (Terms & Conditions Apply). That means if soot builds up again under normal driving and no faults are present, we’ll re-clean it once free of charge. See our FAQs for more details.

Get Proof, Not Promises

Ready to get your DPF sorted properly? Whether you drive in or post your filter, we’ll test it, clean it, and prove the result.

Call 07827533529 or contact us online to book your DPF flow test and cleaning today.