Introduction
When a DPF warning light appears, most garages jump straight to:
• Forced regeneration
• Chemical cleaning
• Or replacement quotes
But a blocked DPF is rarely the root problem.
It’s usually the result of another fault.
The only reliable way to diagnose a DPF issue is through live data. Not guesswork. Not generic fault codes. Real sensor values.
This guide explains exactly how to diagnose a blocked DPF using live data, which parameters to check, what healthy readings look like, and how to identify the true cause of repeated DPF problems.
Why Fault Codes Alone Are Not Enough
Common DPF-related fault codes include:
• P2002 – DPF efficiency below threshold
• P2463 – High differential pressure
• P242F – DPF restriction / ash accumulation
These codes tell you what the ECU sees, but not why it happened.
Live data shows:
• Whether the DPF is genuinely blocked
• Whether regeneration is failing
• Whether another engine fault is creating excess soot
That distinction saves expensive mistakes.
Key Parameters to Log
A proper DPF diagnostic log should include:
• Differential pressure across DPF (mbar)
• Exhaust gas temperature pre-DPF
• Exhaust gas temperature post-DPF
• Calculated soot load (%)
• Distance since last regeneration
• Regeneration status (active/passive)
• Vehicle speed and RPM
Optional but valuable:
• MAF g/s
• Injection quantity
• Lambda
These values together tell the full story.
What Healthy DPF Data Looks Like
At steady motorway cruising:
• Differential pressure: low and stable
• Pre-DPF temperature: 250–400°C
• Post-DPF temperature: slightly lower
• Soot load: gradually rising
• Regeneration: passive or occasional active
After a successful regen:
• Soot load drops sharply
• Differential pressure returns to low baseline
This is a healthy self-cleaning system.
Signs of a Blocked or Blocking DPF
1) High Differential Pressure
Symptoms:
• High mbar readings at idle or light throttle
• Pressure rising quickly with RPM
Indicates:
• Exhaust restriction
• DPF filling with soot or ash
2) Frequent Active Regenerations
Symptoms:
• Regeneration triggered every 50–100 miles
• High exhaust temperatures often
Indicates:
• Excess soot production
• Underlying engine fault
• Short-journey driving pattern
3) Regeneration Fails to Complete
Symptoms:
• Regeneration status active
• Temperatures rise
• Soot load does not drop
Indicates:
• Interrupted regens
• Temperature not reaching burn threshold
• Faulty temperature sensor
• Exhaust leak
4) High Soot Load With Normal Driving
Symptoms:
• Soot load climbing quickly
• Vehicle driven on long journeys
Indicates:
• Over-fuelling
• Faulty injectors
• EGR stuck open
• Boost leak
• Poor remap
5) High Ash Load
Symptoms:
• Soot regen works
• Differential pressure remains high
• Ash load model near maximum
Indicates:
• Permanent DPF filling
• Cleaning or replacement required
Ash cannot be burned away.
Using Live Data to Find the Root Cause
DPF blockages often come from:
• Faulty EGR → excess soot
• Boost leaks → rich combustion
• Weak turbo → low exhaust temps
• Bad injectors → poor atomisation
• Incorrect tuning → excess fueling
Live data exposes these upstream issues clearly.
Fixing only the DPF without fixing the cause leads to repeat failure.
When a Forced Regeneration Is Appropriate
A forced regen is useful when:
• Soot load is high
• No mechanical faults present
• Vehicle has failed passive regens due to driving pattern
But it is not a fix if:
• Differential pressure remains high afterward
• Regens fail repeatedly
• Underlying faults exist
Live data before and after confirms whether the regen actually solved anything.
Why This Matters for Customers
Data-led diagnosis:
• Prevents unnecessary DPF replacement
• Saves money
• Builds trust
• Differentiates professional service from guesswork
Most DPF horror stories come from misdiagnosis, not bad filters.
The Takeaway
A DPF should never be diagnosed by fault codes alone.
Live data tells you:
• Whether the DPF is blocked
• Whether regeneration is working
• Whether another engine fault is causing the issue
Proper diagnosis means:
Fix the cause, not just the symptom.
Need a Proper DPF Diagnosis?
We carry out full live-data DPF diagnostics, identify the true cause of blockage, and advise the correct repair or software solution. No unnecessary replacements. Just accurate answers.