Diesel Trouble Codes

P242F — Diesel Particulate Filter Restriction - Ash Accumulation — L5P Duramax

Diesel Particulate Filter Restriction - Ash Accumulation

Updated October 15, 2026

What it means

The DPF ash load has reached its service limit. On the L5P the DPF needs cleaning or replacement once ash reaches the limit.1

Most likely causes

  1. DPF ash load at service limit — Ash is non-combustible residue from oil consumption and normal operation; it accumulates over time and cannot be removed by regeneration. The ECM sets P242F when modeled ash mass exceeds the service threshold.1
  2. DPF physically clogged or damaged — Internal blockage or substrate damage increases backpressure and can be misinterpreted as ash restriction. Inspect DPF for cracks, melted substrate, or external damage that raises restriction.1
  3. DPF differential-pressure sensor or tubing fault — Erroneous pressure readings can cause the ECM to calculate excessive ash load. Check sensor supply/ground, signal, and pressure tubes for leaks, blockage, or moisture.1
  4. Excessive oil consumption / oil ash ingress — Worn components or injector issues increase oil entering the exhaust, raising ash accumulation rate. Verify oil consumption and address engine oil-related sources before DPF service.1

How to diagnose

  1. Verify freeze-frame and confirm P242F is present with no accompanying DPF pressure sensor circuit codes.
  2. Read DPF ash mass / soot load and distance-since-last-regeneration data with a scan tool. High ash mass supports service limit.
  3. Inspect DPF differential-pressure sensor and tubing for leaks, blockage, or moisture; compare sensor voltage to spec at idle and elevated RPM.
  4. Perform a manual service regeneration if allowed and monitor completion; persistent high ash mass after successful regen indicates ash limit.
  5. Check engine oil consumption and look for signs of oil entering exhaust (e.g., oil in intake, injector leakage). Address oil-related causes before DPF replacement.
  6. If ash mass is at service limit and no sensor faults are present, remove DPF for professional cleaning or replacement per GM service information.

Common mistake to avoid

Cleaning or replacing the DPF before checking its pressure sensor and tubes. Cracked, melted, plugged or wet sensor tubes, or a failing sensor, can set DPF codes while the filter itself is fine. They are cheap to check; clear and verify them before touching the filter. Source: FleetRabbit — P2002 DPF efficiency code causes and fixes.

Parts and tools you may need

Tools you’ll need

Rough cost and difficulty

Likely repairPartsShop laborWho usually does it
Internal engine repair (cost depends on teardown findings)Depends on findingsDepends on findingsShop
DPF differential pressure sensor$80–$3000.5–1.5 hrsEasy DIY
DPF professional cleaning (bake and blow)$300–$7001–3 hrsShop
DPF replacement$1,500–$4,0001–4 hrsShop

Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.

When to see a pro

If the DPF requires removal, cleaning, or replacement, or if oil consumption or engine faults are suspected, have a qualified diesel technician perform the work. Do not attempt high-pressure fuel or exhaust system service without proper training and equipment.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources

  1. Curated DTC seed — L5P Duramax (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎

Repair videos: P242F on the L5P Duramax

Third-party videos, not ours — picked for this engine. Confirm anything against the factory service information for your truck.

How To Test DPF Differential Pressure Sensor. Diagnostic — O'Rileys Autos · 715K views