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6.6L Duramax LML

The 6.6L Duramax LML was introduced for the 2011 model year. It features an advanced exhaust aftertreatment system that includes selective catalytic reduction technology. This aftertreatment system requires the use of diesel exhaust fluid (DEF), a urea based solution that is perpetually injected into the exhaust stream at variable rates to reduce NOx (nitrous oxides) emissions. GM claims that the system reduces NOx levels by 63 percent compared to the previous Duramax LMM. The SCR system was a necessary addition allowing the 6.6L Duramax engine family to continue to meet increasingly stringent Federal emissions regulations. The LML was ultimately retired following the 2016 model year, being replaced by the next-generation L5P.

6.6L LML Duramax Engine Specs, History, & Information

The LML Duramax is a heavily altered derivative of the previous LMM, with General Motors claiming that the updated platform had been engineered with 60% newly designed components (i.e. not carried over from previous models). Topping the list of changes is an updated engine block casting, new oil pump design, higher strength pistons and connecting rods, improved main bearing design, and rerouted oil passages. Additionally, the fuel dilution concerns of the previous LMM were circumvented by the introduction of the "9th injector" (downstream injector), a fuel injector dedicated solely to introducing fuel into the exhaust stream during active regeneration cycles. This technique, as opposed to the post-injection method, significantly reduced fuel dilution and eliminated the cylinder washing concerns that were quickly identified in the LMM. Additionally, the LML became the first generation Duramax diesel to be certified for biodiesel usage in blends up to 20% (B20; 20% biodiesel, 80% petroleum diesel).

Although the implementation of the SCR system was met with heavy scrutiny, it came with the advantage of reduced regeneration cycles and DPF loading rates as it allowed for a more flexible engine calibration that did not rely heavily on air-to-fuel ratio management to reduce NOx emissions. Instead, the new system permits the engine to produce higher NOx emissions since they are ultimately converted by the exhaust aftertreatment system. As a result of the transition to the SCR system and less frequent active regeneration cycles, fuel economy was greatly improved on the LML when compared to the previous generation. GM's official statement on the matter is that the LML achieved an 11% fuel mileage gain over the previous LMM.

6.6L LML Duramax Specs

Engine Family:

6.6L Duramax diesel (Duramax 6600)

RPO Code:

LML

VIN Code:

8 (8th digit of VIN)

Assembly Site:

DMAX engine plant, Moraine, Ohio

Applications/Production Years:

2011 - 2016 Chevrolet Silverado 2500 HD, 3500 HD
2011 - 2016 GMC Sierra 2500 HD, 3500 HD

Displacement:

6.599 liters (6.6 liters nominal), 402.62 CID (403 CID nominal)

Configuration:

90 degree V-8

B10 Life:

Not specified

B50 Life:

Not specified

Bore:

4.055 inches (103.00 mm)

Stroke:

3.897 inches (99.00 mm)

Bore/Stroke Ratio:

1.04 (marginally oversquare)

Compression Ratio:

16.0 : 1

Firing Order:

1-2-7-8-4-5-6-3

6.6L Duramax LML cylinder numbers

Engine Block Material:

Cast gray iron, induction hardened, deep skirt engine block

Cylinder Head Material:

Cast aluminum alloy

Injection System:

Direct injection
Bosch high pressure common rail system, piezoelectric fuel injectors
Bosch CP4.2 injection pump
30,000 psi (2,000 bar) max injection pressure

Aspiration:

Turbocharged, air-to-air intercooler
Water-cooled Garrett GT3788VA variable vane turbocharger (VVT)

Minimum Cylinder Pressure:

300 psi (minimum compression test pressure)

Reciprocating Assembly:

Fracture split forged alloy steel connecting rods
Nitrided forged steel crankshaft
Forged steel camshaft
Cast iron main bearing caps

Valvetrain:

Overhead valve (OHV), standard cam-in-block, mechanical roller lifters
4 valves per cylinder (32 valve)

Cold Start Aid(s):

Traditional glow plug system, 1 per cylinder

Engine Oil Capacity:

10 quarts with oil filter change

Engine Oil Spec:

See viscosity chart at 6.6L Duramax LML service guide

Lube Oil Filter P/N:

ACDelco PF2232

Fuel:

Ultra low sulfur diesel (ULSD) or max B20 biodiesel blend

Peak Horsepower:

397 hp @ 3,000 rpm

Peak Torque:

765 lb-ft @ 1,600 rpm

Idle Speed:

~ 680 rpm @ operating temperature

Governed Speed:

3,450 rpm (electronically governed), ~3,000 rpm max shift speed

Emissions Equipment:

Selective catalytic reduction (SCR, requires diesel exhaust fluid), diesel particulate filter (DPF), diesel oxidation catalyst (DOC), exhaust gas recirculation (EGR) w/ dual EGR coolers & EGR cooler bypass circuit, downstream fuel injector (9th injector)

Coupled Transmissions:

Allison 1000 6 speed automatic

Engine Weight:

Approx. 835 lbs

Engine Dimensions:

Length:

Approx 30.0 inches

Width:

Approx 30.0 inches

Height:

Approx 32.0 inches

6.6L LML Duramax Horsepower & Torque Curves

6.6L Duramax LML horsepower and torque curves

6.6L Duramax LML horsepower and torque curves, 397 hp @ 3,000 rpm, 765 lb-ft @ 1,600 rpm

6.6L Duramax LML Emissions System

The emissions system on the 6.6L Duramax LML includes the following components:

Diesel particulate filter (DPF) - nearly eliminates particulate (soot) emissions by capturing larger particles. When the filter becomes loaded, the active regeneration process is initiated, the exhaust gas temperature is increased by introducing and incinerating fuel in the exhaust stream, and the captured particulates are burned into smaller byproducts that pass through the filter. Active regeneration cycles are estimated to occur at 700 mile intervals, however the actual intervals are largely impacted by the type of driving.

Exhaust gas recirculation (EGR) - an old technology designed to reduce NOx emissions by introducing exhaust gases back into the combustion chamber. The process lowers available oxygen and lowers combustion temperatures, reducing overall NOx emissions. The EGR cooler on the LML features a bypass circuit so that flow will not be impeded in the event that a cooler becomes clogged with soot.

Selective catalytic reduction (SCR) - utilizes and introduces diesel exhaust fluid (DEF), a urea based solution, into the exhaust stream to further reduce NOx emissions. The DEF tank is designed to last approximately 5,000 miles under normal operating conditions, although actual usage rates can vary widely depending on the type of driving/operation. An engine will enter a limp-mode state if the DEF tank is allowed to reach empty (see below for more information).

SCR & DEF System Overview

DEF is injected into the exhaust stream by means of a dosing nozzle, a type of fluid injector that perpetually supplies the exhaust system with DEF. The DEF tank on vehicles equipped with the Duramax LML is approximately 5 gallons in size and is designed to last around 5,000 miles of driving before requiring a refill. On Silverado and Sierra pickup trucks, the DEF tank fill is located under the hood on the passenger side near the firewall. On Savana and Express vans, the DEF tank fill is located in the fuel fill door.

The DEF system will initiate a series of illuminated warnings in the instrument panel display when the DEF fluid level's estimated range reaches 1,000 miles until empty. Subsequent warnings will follow as the DEF level continues to deplete. If the DEF fluid level is completely depleted, an "EXHAUST FLUID EMPTY" message will be displayed and upon the next restart the vehicle speed will be limited to 55 mph. If the tank remains empty, speed will be limited to 4 mph after the second subsequent refueling.

The system also monitors DEF quality. If the quality of the exhaust fluid is identified to be poor (i.e. diluted or otherwise contaminated), an "EXHAUST FLUID QUALITY POOR" message will be displayed in the instrument panel. If the problem is not corrected within 200 miles of driving, the vehicle speed will be limited to 55 mph and eventually 4 mph upon the next refueling. If the DEF system detects that it requires service (i.e. one or more malfunctioning components), a "SERVICE EXHAUST FLUID SYSTEM" message will be displayed on the instrument panel. Failure to service the system within 200 miles will result in speed being limited to 55 mph upon the next restart and 4 mph upon the next refueling.

Diesel exhaust fluid is highly corrosive and may cause severe engine damage if added to the diesel fuel tank; never put DEF in the fuel tank. It is standard procedure to replace the entire fuel system and clean the fuel tank anytime DEF is introduced into the fuel system. This repair bill can run in excess of $10,000 USD. Although the DEF tank location on the LML equipped Silverado/Sierra is widely unpopular and accessibility is limited, particularly on four wheel drive 3500 HD models, it's been placed there to reduce such incidents.

6.6L LML Duramax emissions aftertreatment system schematic

6.6L LML Duramax exhaust aftertreatment components - DOC, SCR, DPF

NOx Sensor Failures & SCR Related Problems

A large percentage of 2011 model year 6.6L Duramax LML diesels endured repeated reliability problems with the SCR and DEF systems. The DEF sensor, NOx sensor, and DEF pump are amongst the most commonly replaced components of the system. Additionally, problems were identified with DEF freezing in cold weather. The predominant reoccurring problem was failures of the NOx sensor, most often identified by a P20EE or P207F diagnostic trouble code (DTC).

Repeated NOx sensor replacements under warranty prompted GM to make significant changes to the design of the sensors and issue a 10 year, 110,000 mile warranty on the updated parts. Owners of what GM considers to be affected trucks were issued correspondences regarding the warranty information, however not all 2011 model year Duramax diesel owners are covered by this extended warranty. It is unknown how many trucks were affected and exactly what the VIN number cut-off was for those covered by the updated warranty. We've received reports of, and experienced similar problems with 2012 model year pickups, but not at the same frequency of the 2011 model engines.

Page Information

Last update: 11/21/2021

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Sources: GM technical data and original spec sheets, applicable owners manuals and Duramax diesel supplements, archived data (gm.com, gmfleet.com, gmpowertrain.com, and in print form)