P246C on GMC: How to Diagnose & Fix
Diesel Particulate Filter Restriction - Forced Limited Power
1 GMC model · 1 documented issue · 1 critical · $300-$3,500 repair
P246C on GMC by model: symptoms, diagnosis and fix
The Duramax diesel DPF becomes clogged with soot under low-speed, short-trip, or heavy towing duty cycles that prevent complete passive regeneration. Owners report the truck entering limp mode, reduced power, and repeated active regen cycles that fail to fully clean the filter. GM TSB 14-06-04-003 addresses regen strategy calibration updates for LML and L5P engines.
Common Symptoms
- Reduced engine power / limp mode activation
- DPF warning light or message on DIC
- Frequent or incomplete regen cycles with elevated exhaust temps
- Excessive fuel dilution in engine oil
- Sulfur or burning smell from exhaust during failed regen
How to Fix
Forced active regen via Tech 2 or MDI scan tool; if clogging is severe, DPF removal and professional cleaning or replacement. Updated ECM calibration per TSB 14-06-04-003. Replacement DPF (ACDelco 84031507 or OEM equivalent) runs $800–$2,500. Extended highway driving after software update can restore function in mild cases.
Sources for this issue (1)
P246C code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P246C mean on a GMC?
P246C stands for "Diesel Particulate Filter Restriction - Forced Limited Power." This diesel emissions code sets when the engine control module detects that the diesel particulate filter (DPF) is so restricted with trapped soot or ash that exhaust backpressure has passed a calibrated limit, and it commands a forced reduced-power (limp) mode to limit exhaust flow and protect the engine and filter. The DPF captures soot from the exhaust and periodically burns it off in a process called regeneration; this code generally means something has been preventing successful regeneration. Ignoring it can lead to eventual filter damage. On GMC it is documented across 1 model: Sierra 3500HD.
What are the most common causes of P246C?
The most common causes of P246C are: Excessive soot buildup from too many short trips that block regeneration, Faulty DPF differential pressure sensor or clogged sensor hoses, Failed or incomplete regeneration cycles, Faulty exhaust temperature sensor, EGR system fault increasing soot production, Fuel injector or other engine fault causing heavy soot, Physically clogged or aging diesel particulate filter. The specific cause varies by vehicle.
How much does it cost to fix P246C on a GMC?
Published repair estimates on GMC range from $300 to $3,500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.