Emissions

P24B4 — Diesel Particulate Filter Soot Load Too High

Severity: medium Drive with care, to a shop

What P24B4 means

The engine control unit uses a differential pressure sensor and a soot model to estimate how loaded the particulate filter is, and it found the level above the allowed limit. Normally the filter burns off soot during periodic regeneration at high exhaust temperature. When regeneration fails or is skipped, back pressure rises and power drops.

Symptoms

  • DPF or check engine light on
  • Reduced power and sluggish acceleration
  • Higher fuel consumption
  • Frequent regeneration attempts, cooling fan running after shutoff
  • Rising oil level from fuel dilution
  • Limp mode

Possible causes

  1. Mostly short trips and city driving that never heat the filter enough
  2. Interrupted regenerations after earlier warnings
  3. Faulty differential pressure sensor or clogged or damaged sensor lines
  4. Faulty exhaust temperature sensors
  5. Injector, EGR valve or fuel delivery problems
  6. Wrong or worn oil with high ash content
  7. Heavily clogged or damaged filter

How to diagnose

  1. Read all codes and freeze frame data, and look for related EGR, boost or injector codes
  2. Check soot load, distance since last regeneration and oil level with a scan tool
  3. Test the differential pressure sensor readings at key-on and under load
  4. Inspect sensor hoses, wiring and connectors for damage or blockage
  5. Compare exhaust temperature sensor readings before and after the filter
  6. Check for exhaust leaks and verify EGR and turbo operation
  7. Run a forced regeneration with a scan tool and check the result

Common fixes

  • Highway drive at steady speed for about 20-30 minutes
  • Forced (service) regeneration with a scan tool
  • Replacing the differential pressure sensor or its lines
  • Repairing root causes such as EGR, injectors or temperature sensors
  • Oil change using the manufacturer-specified low-ash oil
  • Professional cleaning or replacement of a clogged filter

Questions and answers

Can I drive with P24B4?

Briefly, yes, but get a highway drive in soon to let the filter regenerate. Waiting too long can clog the filter so badly it needs professional cleaning or replacement.

How do I clear P24B4?

If there are no other faults, try a long steady highway drive. If the light stays on, you need a forced regeneration and a check for the underlying cause.

Why does my DPF clog so quickly?

Short city trips are the usual reason, but bad sensors, a faulty EGR valve or injector problems can also be behind it. Check these or the issue will 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.