P24AA

Particulate Filter Restriction - Ash Accumulation Performance

P24AA is a generic OBD-II powertrain diagnostic trouble code: Particulate Filter Restriction - Ash Accumulation Performance. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P24AA
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P24AA means

P24AA is set when the ECM determines that the diesel particulate filter has accumulated ash beyond an acceptable threshold, causing a restriction that affects filter performance. Unlike soot, ash is a non-combustible residue derived primarily from engine oil additives that cannot be removed by regeneration and accumulates permanently over the filter's service life.

The ECM estimates ash loading using a long-term model based on mileage, oil consumption history, and differential pressure trends after successful regenerations. When the modeled ash level or the measured residual pressure drop after a completed regeneration exceeds calibrated limits, P24AA is set to indicate that the filter requires servicing or replacement.

This code is typically associated with high-mileage vehicles and is expected to appear as the DPF approaches the end of its service life. It may also appear prematurely on vehicles with high oil consumption or that have used incorrect oil specifications, which accelerate ash accumulation. DPF cleaning or replacement is the normal corrective action.

Common causes

Most-frequently reported root causes when P24AA is logged.

  • 1
    Normal long-term ash accumulation from engine oil combustion byproducts over high mileage.
  • 2
    Excessive engine oil consumption accelerating ash deposition beyond normal age-related rates.
  • 3
    Use of engine oil with a high SAPS (sulfated ash, phosphorus, sulfur) content not approved for DPF-equipped engines.
  • 4
    Coolant leak into the combustion chamber contributing to non-combustible residue deposits in the DPF.
  • 5
    Extended oil change intervals allowing degraded oil to produce higher ash content.
  • 6
    Faulty differential pressure sensor causing premature ash accumulation detection.
  • 7
    Incorrect ECM ash accumulation model reset after a previous DPF cleaning or replacement.

Symptoms drivers notice

MIL illuminated, often accompanied by a DPF service or replacement warning.
Elevated exhaust back pressure measurable even after a successful soot regeneration.
Gradual reduction in engine power and fuel economy as ash restriction increases.
Frequent soot regeneration cycles initiated as the ECM compensates for elevated baseline pressure.
DPF regeneration warning light that remains on even after a forced regeneration.

How to diagnose P24AA

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and read all DTCs; note any oil consumption or fuel system related codes alongside P24AA.
  2. 2
    Review DPF ash accumulation model data and mileage since last DPF service in scan tool live data or service history.
  3. 3
    Check differential pressure after a completed regeneration to confirm elevated residual pressure consistent with ash loading.
  4. 4
    Verify engine oil specification in use and review oil consumption between service intervals.
  5. 5
    Inspect for coolant or oil leaks that could be contributing to premature ash accumulation.
  6. 6
    If ash loading is confirmed, arrange DPF cleaning or replacement as appropriate.
  7. 7
    After service, reset the DPF ash accumulation model in the ECM using the scan tool to clear the fault.

Vehicles where we've handled P24AA

Platforms in our catalogue with confirmed P24AA coverage.

BMW 320D
2016

Related powertrain codes

Frequently asked questions

Can regeneration remove ash from the DPF?

No. Regeneration only burns off accumulated soot. Ash is a non-combustible residue that can only be removed by professional cleaning or DPF replacement.

How long does a DPF typically last before ash becomes a problem?

DPF service life for ash accumulation varies widely by vehicle and oil consumption but is commonly in the range of 100,000 to 150,000 miles under normal conditions.

Will using the correct engine oil prevent P24AA?

Using a low-SAPS oil approved for DPF-equipped engines slows ash accumulation significantly but cannot prevent it entirely over high mileage.

Is DPF cleaning a permanent fix for P24AA?

Professional DPF cleaning can restore filter capacity and clear the fault when combined with an ECM ash model reset, but the DPF will continue to accumulate ash and may require replacement eventually.

Disabling P24AA in software

RaceTune can permanently disable P24AA — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

ECUs with a P24AA disable in our catalogue

Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.

  • Bosch EDC17C50 verified 1 software version

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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