My 2011–2016 Duramax shut off and won't restart. Is it the CP4 pump?

Short answer: On the LML Duramax (2011–2016 HD trucks), an engine that suddenly dies and won't restart, sometimes with fuel pressure codes, is often a failed Bosch CP4 high pressure fuel pump. When it fails it can shed metal through the injectors, rails, lines and tank, so the fix is replacing most of the fuel system. Owners report $10,000–$15,000 bills. Some convert to the older-style CP3 pump to avoid a repeat.

Symptom: The engine shuts off while driving or at a stop and won't restart, a hard start or rough running beforehand, a check engine light with fuel rail pressure codes, or metal flakes found in the fuel filter.

What to check first

1. Get off the road safely. You lose power, and power steering assist gets heavy once the engine stops.
2. Don't keep cranking it. A failed pump can push more metal through the system.
3. Have the fuel filter cut open or inspected for metal, and the codes read (a fuel pressure code such as P0087, fuel pressure too low, can show up).
4. Call your insurance company. Owners say some policies covered this repair.
5. If you're near the 5-year/100,000-mile powertrain warranty, have the dealer call GM for help before you pay.

Likely causes

1. Failed CP4 high pressure fuel pump. Owners on Duramax Forum and Diesel Place describe the CP4 failing without warning and sending metal through the whole fuel system.
2. Water or poor fuel. Owners recommend extra filtration, a lift pump and keeping water out of the fuel to improve the odds.

What it usually costs

A 2016 GMC 2500 Denali owner was quoted $15,000 at the dealer for a full fuel system replacement; others said $10,000–$11,000 had been more common. On Diesel Place, one owner's pump failed at 68,000 miles and the $10,500 repair was covered by warranty, and another was quoted $12,000 out of warranty. One owner whose truck was 9,000–10,000 miles past warranty said GM covered it after his dealer called. Owners say a CP3 conversion kit from an independent shop can keep the total under $10,000.

Is it safe to keep driving?

No. If the pump fails the engine can shut off in traffic with no warning. Have it towed. If yours is still running fine, there's nothing to do but maintain it well. Verify with a mechanic.

DIY or shop?

Shop for most owners. Some experienced owners install CP3 conversion kits themselves, but the trucks usually need a tune adjustment afterward and contaminated parts must all be replaced.

Recalls, bulletins and complaints in plain words

• No recall covers the CP4 pump on these trucks. NHTSA's recall list for these years only shows separate dual-fuel-tank sensor recalls on gas-engine 3500s.
• NHTSA complaints: 167 keyword-matched complaints for Chevrolet Silverado 2500 and 3500 HD 2011–2016 (of 1,164 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-18; keywords: fuel pump, cp4, cp-4, high pressure, injection pump, metal, fuel system, stall) (NHTSA returned no complaint data for 24 model-year queries).

What owners report

• In 2016 CP4 fuel system replacement on Duramax Forum, a 2016 GMC 2500 Denali HD owner's engine shut off as he pulled onto his street; the dealer quoted $15,000 for the whole fuel system. Members said $10,000–$11,000 used to be typical, suggested an independent shop and a CP3 conversion, and said to check insurance.
• In Have they fixed the CP4 issue yet? on Diesel Place, owners shared failures: one at 68,000 miles cost $10,500 under warranty, another was quoted $12,000, and one owner just past warranty got GM to cover it. Others recommended a lift pump with extra filtration and keeping the tank full.

My take

My advice as a former finance manager: if you're buying a used LML, ask whether the CP4 has been converted or replaced, and price an extended service contract that clearly covers the fuel system. Read the exclusions. This is the repair that sinks budgets.

Vehicle focus: 2011–2016 Chevrolet Silverado 2500HD and 3500HD and GMC Sierra 2500HD and 3500HD with the 6.6L LML Duramax.

Safety / mechanic note

A failed pump can shut the engine off in traffic. Verify with a mechanic.