P242F — Diesel Particulate Filter Restriction - Ash Accumulation — 6.7 Cummins (EGR + DPF, pre-SCR)

Diagnostic reference for 6.7 Cummins 2007.5–2012 (EGR + DPF, pre-SCR).

Updated October 15, 2026

What it means

P242F is Diesel Particulate Filter Restriction - Ash Accumulation. Generic definition: the DPF ash load has reached its service limit. On the 6.7L Cummins ash does not burn off in regeneration; at high mileage the DPF needs cleaning or replacement. Excess oil consumption speeds ash build-up.¹

Most likely causes

1. High-mileage DPF ash loading requiring service — Ash is incombustible residue from oil additives and normal wear. Over time it accumulates in the DPF substrate and raises backpressure. On this platform ash does not burn off in regeneration; at high mileage the DPF needs cleaning or replacement.¹
2. Excess engine oil consumption increasing ash input — Worn valve seals, turbo seal leakage, or blow-by can increase oil entering the exhaust. More oil raises ash accumulation rate and can trigger P242F earlier.¹
3. DPF differential-pressure sensor or hose fault causing incorrect ash-load calculation — A faulty DPF differential-pressure sensor or plugged/cracked sensor hoses can skew the calculated ash load and set P242F. Check the DPF pressure sensor hoses (cracked, melted or plugged) and the sensor; a bad reading upsets regeneration.²

How to diagnose

1. Verify freeze-frame and mileage; confirm sustained high DPF differential pressure at idle and cruise consistent with ash loading rather than transient soot.
2. Inspect DPF differential-pressure sensor and tubing for cracks, melting, oil contamination, or blockage; compare live differential pressure to expected values at idle and 2000 rpm no-load.
3. Review oil consumption history and inspect for sources of oil ingress to exhaust (turbocharger seals, valve seals, crankcase ventilation).
4. If sensor and plumbing are correct and pressure remains high, perform DPF ash-load service assessment per Cummins procedure; cleaning or replacement is required because ash does not burn off in regeneration.

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

• DPF differential pressure sensor
• DPF pressure sensor hoses
• DPF cleaning service or replacement DPF
• Oil consumption inspection items (turbocharger, valve seals, crankcase ventilation)

Tools you’ll need

• diesel exhaust fluid compatible scan tool — Reads DPF differential pressure, ash load, and regeneration data to confirm ash restriction versus sensor fault.
• digital multimeter — Tests DPF differential-pressure sensor supply, ground, and signal voltages against spec to rule out electrical faults.
• manometer or differential pressure gauge — Directly measures exhaust backpressure across the DPF to verify high restriction consistent with ash loading.
• borescope — Inspects DPF inlet/outlet and sensor tubes for soot plugging, oil contamination, or physical damage without removal.

Rough cost and difficulty

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 high exhaust backpressure is present, do not attempt high-speed road testing. Have a qualified diesel technician confirm differential pressure readings and perform DPF ash service or replacement using proper handling procedures.

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