2011-2014 GMC Duramax LML Parts & Upgrades

What GM changed for the 2011 Sierra HD

The Sierra HD carried its 2007-2014 cab into 2011 and got an entirely new chassis under it. Eleven fully boxed frame assemblies raised bending stiffness by 92 percent and torsional stiffness by roughly five times. Forged-steel upper and cast-iron lower control arms ride on five torsion-bar rates matched to front axle weight, the rear went to three-inch-wide asymmetrical leaf springs — two-stage on the 2500HD, three-stage on the 3500HD — and the brakes went to 14-inch rotors front and rear with stiffer calipers and hydroboost assist run off the power steering pump. A larger steering gear and a higher-pressure pump came with it. Towing is the point of all of it: a 2011 Sierra 3500HD was rated up to 16,000 lb conventional and 20,000 lb fifth-wheel or gooseneck at a 27,500 lb GCWR, with payload to 6,335 lb and GVWR as high as 13,000 lb, while the 2500HD topped out at 13,000 lb conventional. Trailer sway control and an integrated trailer brake controller were part of the package, and the exhaust brake works through the turbo's vanes rather than a separate butterfly. The engine is the fifth-generation 6.6L Duramax: a 90-degree V-8 with four valves per cylinder, a cam-in-block pushrod valvetrain, 16.0:1 compression, 397 hp at 3,000 rpm and 765 lb-ft at 1,600 rpm, assembled at DMAX in Moraine, Ohio. Behind it the Allison 1000 six-speed, RPO MW7, runs 3.10 in first through 0.61 in sixth; no manual was ever offered. The rear axle is the AAM 11.5-inch with its 14-bolt cover, 3.73 standard and 4.10 available, and 4WD trucks use the AAM 9.25-inch independent front differential. Trims ran WT, SLE, SLT and Denali across Regular, Extended and Crew Cab, with the 3500HD in single or dual rear wheel.

Where these trucks give trouble

Start with the simple faults, because they imitate the serious ones. Factory charge-air boots split or blow off and the crimp-style clamp on the center silicone boot gives up, which reads as a whoosh or whistle, smoke, lost power and an underboost code P0299. On the turbo, the Garrett GT3788VA's bearings are rarely the issue — the vane position sensor is, and it shows up as lag, soft throttle response, reduced power and P2563 or P003A. The oil-pressure vane solenoid is the other half of that job and should measure 3.4-4.2 ohms at about 73 F. Up-pipes crack at the bellows and leak exhaust ahead of the turbo, which you hear as a tick under the hood and see as soot around the joint. Cold-start complaints usually land on the glow plugs and the glow plug control module mounted on the driver's side of the turbo near the firewall, covered by GM bulletin PIP5217, with per-cylinder codes P0671 through P0678 or circuit codes P0380 and P0382 — but a cold start pulls around 120 amps for the plugs and the intake heater, so look at both parallel batteries and the cables before condemning anything. The front end wears the way every heavy independent-front-suspension truck wears: idler and pitman joints loosen on high-mileage trucks, the factory tie rods are light for the weight and lighter still under oversize tires, and the result is wander, a clunk when you turn and tires worn unevenly. Shocks fade somewhere past 60,000 miles and a leveled truck on stock dampers rides harsh; rear leaves sag on trucks that live loaded. Behind the engine, the Allison's C3 clutch pack only sees fluid when it is applied and runs hot, the 2011-and-up TCM drops main line pressure to about 80 psi at cruise to save fuel, and the converter's thin stator and flexing front cover are what let go first under heavy towing. Normal transmission temperature is 175-195 F, 205-215 F is expected with a trailer, and anything sitting over 220 F is a warning, with 240 F the stated ceiling. On the cooling system, water pump seals and bearings commonly fail around 100,000 miles, the mild-steel bypass tube between the pump and the thermostat housing rusts and seeps at its O-rings, a surge-tank cap that no longer holds pressure is the usual answer to coolant that vanishes with nothing on the driveway, and a thermostat fitted upside down or at the wrong rating will build pressure and push coolant out the overflow. EGR cooler clogging appears on the common-failure lists for this engine. Short-trip trucks load the particulate filter with soot and ash and regen constantly, and NOx sensor failure is the most common emissions-system fault on the platform, heavily documented on 2011 trucks, which received extended coverage — expect a Service Emissions System message, a P20EE that returns after a clear, and a countdown toward derate.

Then there is the fuel system, which is why this engine has the reputation it has. There is no factory lift pump: the gear pump inside the Bosch CP4.2 pulls from the 36-gallon tank through the passenger-side filter head with its manual primer and water-in-fuel sensor, then feeds twin rails and eight piezo injectors at roughly 30,000 psi — and that same diesel is the pump's only lubricant. US ULSD is thinner than the fuel the CP4.2 was designed around. Most failures arrive with no warning at all; when there is one, it is long cranking, a stall that will not restart, surging or hesitation, a rhythmic knock from the pump, or a low rail pressure code such as P0087. What makes it such a big repair is where the debris goes: through the rails, the injectors and the high-pressure lines, and back toward the tank. The piezo injectors themselves hold up well — nearly every damaged set we open up is downstream of a pump. Two details worth knowing on this platform: GM left off the fuel cooler the LMM had, which is cited as one reason pump temperatures sit higher, and the filter head itself can crack and let air in or fuel out, so a fuel smell with hard starting and a stumble is worth a look before you assume the worst.

If your Sierra works for a living

Towing hardware comes first on a work truck. A deep transmission pan and an auxiliary cooler hold towing temperatures under about 215 F, and a plug-in monitor on the OBD-II port shows transmission temperature, EGT, boost, rail pressure, DEF level and regen status without touching a calibration; a 52 mm gauge-mount unit of the Banks iDash class reads dozens of CAN parameters and logs to a card, though some kits ship without an OBD-II cable because they are built to daisy-chain off a pedal module. If you pull heavy, a billet-cover multi-disc converter and TCM tuning to lift that 80-psi cruise pressure are the two changes that earn their keep, and they belong together. Rear air springs of the LoadLifter 5000 type cover 2011-2019 2500 and 3500 trucks, run 5-100 psi and level up to 5,000 lb. An underbed gooseneck ball of the B&W Turnoverball type bolts to existing frame holes on 2011-2015 trucks with 6.5 or 8-foot beds, takes a single four-inch hole in the bed floor, is rated to 30,000 lb gross trailer weight and 7,500 lb tongue, and accepts a drop-in fifth-wheel adapter. A higher-plate-count engine oil cooler and a finned aluminum cover on the AAM 11.5 add oil volume and heat capacity for grade work.

If you are keeping it for the long haul

Everything on a high-mileage LML starts at fuel supply. A lift pump with filtration of the FASS Titanium or AirDog class gives the CP4.2 positive, de-aerated fuel through water separation ahead of a fine final filter, mounts to the bed bolts and taps the factory lines, and it is the one upgrade worth doing whatever your power goals are. Pair it with a case-return bypass kit so a failing pump pushes its debris toward the tank side instead of the rails, and a fuel pressure regulator with a screen that will not collapse. Run a lubricity additive every tank, keep the tank above a quarter, never run it dry, shorten the fuel filter to a 10,000-mile interval and cut the old one open to look for glitter. Owners who want the question closed for good go to a CP3: the S&S Diesel Motorsport 50-state kit carries CARB Executive Order D-756-4, needs no tuning, keeps the factory fuel pressure regulator and leaves every emissions component where GM put it, and it is about two days in the bay. On the cooling side, swap the mild-steel bypass tube for stainless with fresh O-rings while the water pump is off, choose a pump with a cast metal impeller, and pressure test the system rather than guess when coolant is going somewhere. Trucks that tow in Florida heat can take a high-flow or lower-temperature thermostat kit and a thicker-core aluminum radiator. If the heads ever come off, ARP studs and a correct multi-layer gasket are the standard move, though a stock-power truck rarely needs them. High-flow manifolds and up-pipes with stainless bellows end the cracked-bellows problem permanently.

Leveled, lifted and stopped

The 2011 chassis carried straight through the 2015 body change, which is why suspension parts are catalogued 2011-2019 and why nothing from a 2001-2010 truck fits. BDS Suspension builds 4.5-inch and 6.5-inch kits with a no-torsion-bar-drop design, plus coilover conversions that clear 35-inch tires on a diesel 4WD. Bilstein 5100 and B8 dampers, Fox and Rancho units cover the shock side. Once the truck is leveled and on wide tires the front end needs help: aftermarket upper control arms are called for past about 11.50 inches of tire width, heavy-duty tie rods and sleeves replace the light factory pieces, a pitman-and-idler support brace takes the slop out of the linkage, and severe-duty pitman and idler arms are there when the originals are worn. Have it aligned to the published 2011-2019 recommendations after any of that work. Lifetime-warranty tapered-roller front hubs are listed 2011-2019 in both single and dual rear wheel and both drivetrains. For brakes, drilled and slotted rotors with ceramic pads are offered for SRW trucks, and stainless braided lines — with extended fronts for lifted trucks — firm up the pedal on a hydroboost system.

Compliant power on the air side

What we list keeps the aftertreatment intact and carries paperwork. A CARB-exempt intake is the usual first move: the S&B 75-5075-1 covers 2011-2016 under EO D-590-15 with a cleanable KF-1062 element, and the Banks Ram-Air carries EO D-161-146. A larger intercooler of the Techni-Cooler 25988 type (EO D-161-114) adds most of a core's worth of volume and a much larger inlet, and the matching 25993 boost tube for 2012-2016 trucks (EO D-161-123) ends the blown-boot cycle with heavier silicone and constant-tension clamps. A DPF-back exhaust in four or five inch, aluminized or stainless, fits 2011-2019 and leaves every emissions component in place; a high-flow downpipe is available under CARB EO D-763-2 in the V-band version for 2011-2015 trucks. On the turbo, a drop-in variable-vane unit in the 63.5-66 mm range keeps the factory vane control and the exhaust brake while raising the airflow ceiling, and a larger inlet mouthpiece with three-inch cold-side piping and a CNC Y-bridge relieves the factory restriction. A healthy turbo with soot-stuck vanes is usually better cleaned than replaced — Roloc discs on the unison ring, high-temperature anti-seize on reassembly, and a hard pull now and then to keep the vanes moving. Injectors get matched to the fuel system, not ordered ahead of it.

Brands and part types on this page

The service side leans on Merchant Automotive — engine gasket sets, Allison converter-housing reseal kits, deluxe fuel filter head rebuild kits, water-in-fuel sensor O-rings, pass-through transmission connector seals, starter solenoids — with Mahle lower engine gasket kits and oil pan gaskets alongside, ACDelco TP3018 fuel filters, Allison gaskets, and Alliant Power injector, VGT and IPR pigtails. For the fuel system there are S&S Diesel Motorsport injectors, Exergy Performance fuel-system parts, FASS extreme water separator elements and S&B KF-1062 replacement filters. Pacific Performance Engineering covers chassis and engine-bay hardware with forged XR tie rod kits, drilled steering assembly kits, a diesel lift pump, Micropure XR oil filters and billet aluminum odds and ends, and BDS Suspension brings lift kits and heavy-duty tie rod kits. XDP MFG supplies the Xtra Cool direct-fit radiator and fuel filter adapter wrenches; Mishimoto Performance Parts and BD Diesel cover cooling and drivetrain hardware; Wehrli Custom Fabrication adds fabricated charge-air and engine-bay parts; MBRP handles exhaust with universal 409 stainless mufflers and resonators in aluminized and stainless steel; G&R Diesel lists turbo drain kits and Mean Green high-output alternators. Fluids and chemicals are Hot Shot's Secret Green Diamond CK-4 engine oils and fuel additives plus Lucas Oil. Edge Products covers monitoring with Insight CTS3 displays, EGT kits and pressure senders. The LML service tools are here too, the vane position sensor socket and the fuel filter head wrench being the two you cannot work around. Some items in the grid are universal-fit, so read the fitment line on the product page rather than assuming everything here is Sierra-specific.

Ordering for a Sierra

Body and lighting parts are make-specific: Sierra housings are not Silverado housings, so order by make as well as year. A 2011-2014 Sierra HD follows the 2007-2014 HD fitment for headlights, taillights, running boards, fender hardware and interior pieces, and none of it carries to the 2015-2016 trucks, which got a new cab. Mechanical parts run the other way, because the 2015 change was a body and not an engine, so engine hard parts generally cover 2011-2016. The exception is the turbo-to-downpipe joint, a V-band through early 2015 and a three-bolt flange from 2015.5, so turbos and downpipes have to match what is on the truck; DPF-back systems are also sold by cab and bed length, and dual-rear-wheel trucks route the tailpipe differently. Brake pads split three ways across this run — 2011, 2012-2014 and 2015-2019 — and again SRW versus DRW, so confirm whether the truck is a dually before ordering rear parts. Hubs are their own part for 2011-2019 in SRW/DRW and 2WD/4WD versions, which is also why you check the bolt pattern on the truck instead of against an older wheel. Air-side parts are the fussiest: intake kits are year-split inside 2011-2016 for some brands and a single part number for others, and charge-pipe kits are listed 2011 separately from 2012-2016. Order the vane position sensor by engine code, since the 763527-0712 unit covers LBZ, LMM and LML while the LLY takes a different sensor. Glow plug sets are listed 2006-2011 by one brand and 2006-2016 by GM, and the glow plug control module changed after 2012, so order those by exact year. NOx sensors are listed 2011-2014 separately from 2015 and 2016 and by upstream or downstream position, and the DEF tank reservoir is a 2011-only part. Underbed gooseneck kits are listed 2011-2015, and 2016 trucks that could be ordered with the factory gooseneck prep package take a different kit, so verify the year and whether that package is there; the gooseneck hole centers 44.75 inches from the rear of a short bed and 49.5 inches on a long bed, and air spring brackets need frame drilling when a gooseneck bracket already occupies the U-bolt location. One VIN check before any of it: the eighth digit is an "8" on an LML. The detuned LGH shares the engine family but never went into a Sierra pickup — it went into vans, and for 2011-2012 into some 3500HD chassis cabs at 335 hp and 685 lb-ft — so anything rating- or calibration-dependent has to match the VIN. Tuning and emissions-related hardware is listed only when it carries a CARB Executive Order; check that the order covers your exact model year.

Frequently asked questions

What does a Sierra HD Denali need that an SLE or SLT does not?

Mechanically, nothing. Every 2011-2014 Sierra 2500HD and 3500HD diesel got the same LML, the same Allison 1000 and the same AAM axles whatever the trim, so engine, fuel, cooling, brake and driveline parts are ordered by year, cab, bed and single-or-dual rear wheel rather than by badge. Trim only matters on the outside and inside: grille, lighting and bumper parts are make- and year-specific, and the Denali's are its own. Order those by make and model year, and send us the VIN if you are not sure which you have.

Can my 2011 Sierra 3500HD really pull 20,000 pounds?

Twenty thousand is the fifth-wheel and gooseneck figure for a 2011 3500HD, alongside 16,000 lb conventional, a 27,500 lb GCWR and GVWR as high as 13,000 lb; a 2500HD stops at 13,000 lb conventional. Which rating applies to your truck depends on cab, drivetrain, axle ratio and whether it is single or dual rear wheel, so go by the label in the door jamb and not the brochure maximum. At those weights the hardware matters more than the number: a gooseneck rated well past the trailer, air springs to take out the rear sag, and an eye on transmission temperature, which should stay in the 205-215 F band with a load behind you.

My Sierra whistles and feels soft under boost. Is the turbo done?

Usually not. Check the charge-air boots and the crimp-style clamp on the center silicone boot first; a split or blown boot produces exactly that whoosh, the smoke, the lost power and a P0299 underboost code. If the plumbing is tight, the vane position sensor is next, and it fails often enough on this Garrett unit to be treated as a wear item; look for P2563 or P003A. The vane solenoid is the third check and should read 3.4-4.2 ohms at about 73 F. Vanes stuck with soot are a cleaning job, not a new turbo.

Long cranks on cold mornings — glow plugs?

Maybe, but start at the batteries. A cold start pulls roughly 120 amps for the eight glow plugs and the intake air heater, both batteries sit in parallel, and corroded cables or one tired battery will give you the same long crank, white startup smoke and rough idle. If voltage holds up, the plugs and the glow plug control module on the driver's side near the firewall are next; GM addresses those concerns in bulletin PIP5217, and the codes run P0671 through P0678 by cylinder or P0380 and P0382 on the circuit. Order by exact model year, because the controller part changed after 2012.

What does regular service on one of these actually look like?

Engine oil is ten quarts of 15W-40 CJ-4 or CK-4, 5W-40 below 0 F, on the oil life monitor or 10,000 miles. The air filter is a 45,000-mile or four-year item and coolant is DEX-COOL in a 7.125-gallon system. On the Allison, GM calls for the external spin-on filter at 45,000 miles and a full service at 97,500 miles on the normal schedule or 45,000 under severe duty; DEXRON VI is the specification, and the heavier synthetic many owners run is a preference rather than a requirement. We shorten the fuel filter to 10,000 miles on these trucks and cut the old one open. And the obvious one: diesel exhaust fluid goes in its own filler only, because in the diesel tank it is corrosive enough to take the whole fuel system with it.

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