Emissions

P24AF — Particulate Filter Regeneration Incomplete

Severity: medium Drive with care, to a shop

What P24AF means

The engine control unit began a forced burn-off of soot in the particulate filter, but the cycle was interrupted or did not reach its goal. Regeneration normally raises exhaust temperature, often with extra fuel, while temperature and differential pressure sensors monitor progress. If soot remains, the ECU stores the code and turns on the warning light.

Symptoms

  • Check engine or DPF warning light on
  • High soot load shown on a scan tool
  • Higher fuel consumption
  • Loss of power or limp mode
  • Cooling fan running longer, hot exhaust after shutdown
  • Frequent regeneration attempts

Possible causes

  1. Regeneration interrupted by the driver: engine shut off mid-cycle, repeated short trips
  2. Another fault that made the ECU abort the regeneration
  3. Insufficient fuel dosing for heating: injectors or dosing system
  4. Exhaust gas temperature too low (EGT sensors, oxidation catalyst)
  5. Faulty differential pressure sensor or clogged sensor hoses
  6. Heavily clogged or damaged particulate filter
  7. Exhaust leak

How to diagnose

  1. Read all codes and freeze frame data and fix related faults first
  2. Check soot load, distance since the last regeneration and oil condition (fuel smell, rising level)
  3. Review exhaust temperature and differential pressure sensor readings, cold and running
  4. Inspect pressure sensor hoses and wiring for cracks, blockage and corrosion
  5. Check injectors, fuel pressure and the dosing system
  6. Inspect the exhaust for leaks
  7. Run a service regeneration with a scan tool and watch filter inlet temperature
  8. If it will not regenerate, assess whether the filter needs cleaning or replacement

Common fixes

  • Perform a forced (service) regeneration with a scan tool
  • Drive 20-30 minutes at steady highway speed as the manufacturer recommends
  • Replace faulty temperature or pressure sensors
  • Repair injector or fuel delivery problems
  • Change engine oil if diluted with fuel
  • Clean or replace the particulate filter

Questions and answers

What does P24AF mean?

The control unit started burning off soot in the particulate filter, but the process did not finish. Soot remains in the filter, so the code was set.

Can I drive with P24AF?

For a short time, yes, but the longer you wait the more the filter clogs. Find the cause soon and complete a regeneration.

How do I clear P24AF?

Fix the cause first and complete a regeneration, either with a scan tool service procedure or a highway drive. Just clearing the code without that will let it return.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.