GMC Duramax Diesel Parts

Engines in the Sierra and Canyon

Three separate engine families carry the Duramax badge on a GMC, and mixing them up is the most expensive mistake in diesel parts buying. The 6.6L V8 is the heavy-duty engine, fitted to the Sierra 2500HD and 3500HD in single and dual rear wheel form across every trim from the work truck to the SLT, AT4 and Denali. It arrived as the LB7 in 2001, became the LLY in 2004.5, the LBZ for 2006 and the 2007 Classic, the LMM for 2007.5 through 2010, the LML for 2011 through 2016, and the L5P from 2017 forward. Separately, the Sierra 1500 carries the 3.0L LM2 and LZ0 inline-six, and the Canyon carries the 2.8L LWN four-cylinder. A half-ton or a Canyon takes none of the 6.6L hardware.

Buying for an older Sierra

Age changes what goes wrong. An LB7 keeps its Bosch injectors under the valve covers in brass cups, so injector work and valve cover work are the same job, and a truck burning oil or running rough usually needs that area opened up. The LLY carries the LB7 bottom end behind a larger variable-geometry turbo, and its cooling system is the part that struggles once the truck is working or towing. The LBZ is the one owners chase: no particulate filter, GM had already sorted the LB7 injector and LLY cooling complaints, and the faults left are small ones such as injector harness chafe, the 2006 glow plug module, water pumps and the leaks any twenty-year-old truck develops. The LMM carried that long block forward with emissions hardware attached, and its pistons can crack from the six-hole spray pattern on a heavily tuned truck, though a stock one commonly runs 250,000 to 400,000 miles.

The LML fuel system, and what the L5P changed

If you own a 2011 through 2016 Sierra, the fuel system deserves your attention before anything else on the truck. The Bosch CP4.2 pump takes its only lubrication from the diesel passing through it, GM fitted no lift pump from the factory, and a pump that comes apart pushes metal downstream into the rails and injectors, which turns a pump job into a fuel system job. Owners protect it with a lift pump, finer filtration and a lubricity additive from our fuel additive range, and with a CARB-numbered CP3 conversion where that is legal where you live. GM solved this for 2017: the L5P was a clean-sheet engine with the first factory lift pump the Duramax ever had and a Denso HP4 pump in place of the Bosch unit. Complaints on a 2017-and-later Sierra skew toward connectors, glow plug modules and sensors rather than hard parts, and the 2024 revision lifted output to 470 hp and 975 lb-ft.

Brands on the GMC side

Our GMC shelves lean on the same specialists our bays do. Pacific Performance Engineering and Wehrli Custom Fabrication between them cover coolant, oil and fuel hard parts across the whole 6.6L run. Merchant Automotive is where we go for Allison and driveline work, which on a Sierra matters as much as the engine. Fleece Performance Engineering and BD Diesel handle fuel and transmission upgrades, Mahle and Alliant Power the gaskets and OE-grade service parts, Mishimoto the cooling side, MBRP the exhaust, BDS Suspension the lift and leveling work, and Hot Shot's Secret the oil and additives. Injectors, turbo hardware, intakes and filters fill in around them.

Before you order

Two model years on the Sierra are split down the middle. A 2004 is an LB7 early in the run and an LLY later, and a 2007 is either an LMM or an LBZ-powered Classic, so the year on your registration does not settle it by itself. Beyond that: single and dual rear wheel 3500 trucks differ through the brakes, axles and hitch hardware; Sierra 2500HD and 3500HD parts do not fit a Sierra 1500, which is the 3.0L inline-six; Canyon parts are their own thing entirely; and the Savana vans and TopKick medium-duty trucks share engine families with the pickups but sit on different chassis, so treat their parts as separate. When the model year is not enough, your VIN and the door jamb build date are.

Frequently asked questions

Are GMC and Chevrolet diesel parts interchangeable?

On the heavy-duty trucks, almost always. A Sierra 2500HD and a Silverado 2500HD of the same year share the Duramax, the Allison and nearly all of the driveline and engine hardware, so a part listed for one normally fits the other. Body panels, grilles, lighting and trim are where the two diverge, so check fitment on anything you can see from outside the truck.

Which Duramax should I look for in a used Sierra?

Owners who want the least trouble tend to shop the LBZ from 2006 and the 2007 Classic, because its known faults are small and inexpensive next to the injector and pump problems that bracket it. An L5P from 2017 on is the other sound answer if the budget reaches, since it was a new engine with a factory lift pump and a different high-pressure pump. Whatever you buy, budget for fuel system maintenance on a 2011 through 2016 truck.

Do you stock parts for the Canyon 2.8L?

We do, and it has its own section in the menu above rather than sitting with the 6.6L parts. The LWN is a 2.8L four-cylinder with a complete Denso injection system, not a Bosch one, so guidance written for the CP4 trucks does not apply to it. Its big scheduled item is a toothed timing belt on an interference engine at 150,000 miles, which is not a job to put off.

What about the 3.0L Sierra 1500?

The 3.0L LM2 and LZ0 inline-six is a different engine from the 6.6L and takes none of its parts. Its timing chains, high-pressure pump drive and oil pump belt all sit at the back of the block against the firewall, which is why so much work on it turns into a transmission-out or cab-off job. Plan labor accordingly and order from the 3.0L pages.

Can I have the work done at your shop?

Yes. Southern Diesel Supply is a working diesel repair shop in Wildwood, Florida, and the parts listed here are the ones we fit for customers. Buy and book the job together if you are nearby; if you are further out, call and we will confirm the right part for your Sierra before it ships.

Not sure what fits your Sierra? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell.