Exhaust
Diesel Particulate Filter
The DPF traps soot from a diesel engine and burns it off during regeneration.
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Exhaust flow
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What it does
- Traps particulate matter (soot)
- Regenerates by burning soot at high temperature
- Monitored by differential pressure sensors
When it fails
- DPF warning light
- Limp mode (reduced power)
- Poor fuel economy
- Failed emissions test
How to diagnose
- Read DPF soot load and pressure sensors
- Check the regeneration happened recently
- Long-motorway drive may complete a regen
- Check for oil dilution from failed regens
Maintenance
- Drive regularly at speed to allow regeneration
- Use the correct low-ash oil
- Never remove the DPF where it is illegal
Use the diagnosis order. When a part fails, confirm each hypothesis with measurements before replacing anything — codes and symptoms overlap.
Related part
Catalytic Converter
The catalytic converter turns harmful exhaust gases into less harmful ones.