LLY Duramax: years, specs & known problems

By CarWhere Research · Updated

The LLY is the second-generation 6.6L Duramax, used from mid-2004 through 2006 in Silverado and Sierra heavy-duty pickups and identified by an 8th VIN digit of 2. It is rated 310 hp and added a Garrett variable-geometry turbo and EGR. Its best-known weakness is overheating while towing, followed by head gaskets.

GM introduced the LLY midway through the 2004 model year to meet tighter emissions rules. It kept the LB7's bore, stroke, block and CP3 pump, but moved the Bosch injectors outside the valve covers, added a valley-mounted EGR cooler and catalytic converter, and switched to an electronically controlled Garrett GT3788VA variable-geometry turbocharger. Torque rose from 520 lb-ft at launch to 605 lb-ft for 2006, and the 2006 LLY uses many parts that do not interchange with 2004–2005 engines.

The LLY combined the smallest radiator fitted to any Duramax with the extra heat load of an EGR cooler, so sustained towing in hot weather is where it struggles. Owners report fan-clutch, water-pump and clogged-radiator problems feeding that heat, and the higher drive pressure from the restrictive turbo inlet is linked to head-gasket failures over time.

LLY Duramax at a glance

GM 6.6L Duramax LLY V8 turbo-diesel (RPO LLY): model years, fuel and peak GM-published output
EngineModel yearsFuelPeak hpPeak torque (lb-ft)Documented problemsRecalls
GM 6.6L Duramax LLY V8 turbo-diesel (RPO LLY)2004.5–2006Diesel31060530

CarWhere lists 3 documented problems and 0 NHTSA recalls for the LLY Duramax, each with a source. Part of the 6.6L Duramax family.

LLY Duramax specifications

LLY Duramax: design facts (2004.5–2006)
SpecificationValue
Displacement6.6 liters (403 cu in), 90-degree V8[3]
Bore × stroke103 mm × 99 mm (4.06 × 3.90 in)[3]
8th VIN digit2[3]
Compression ratio17.5:1[1]
Fuel systemBosch common rail with CP3 pump; solenoid injectors mounted outside the valve covers[1]
TurbochargerGarrett GT3788VA variable-geometry, electronically controlled vanes[1]
Emissions hardwareEGR valve and valley-mounted EGR cooler; catalytic converter after the turbo[1]
TransmissionAllison 1000 five-speed automatic (the six-speed arrived with the LBZ)[4]
2006 changes2006 LLY differs substantially from 2004–2005 engines; many parts do not interchange[5]

LLY Duramax horsepower and torque by year

LLY Duramax: GM-published horsepower (hp) and torque (lb-ft) by model year and application
Model yearsApplicationHorsepower (hp)Torque (lb-ft)Source
2004.5–2005Silverado/Sierra HD pickup310 hp at 3,000 rpm; 520 lb-ft at 1,600 rpm310520[1]
2006Silverado/Sierra HD pickupTorque raised to 605 lb-ft at 1,600 rpm for 2006310605[2]

"—" means we could not confirm the figure from a primary source.

Which GM vehicles have the LLY Duramax?

GM models and model years offered with the LLY Duramax
ModelModel yearsNotes
Chevrolet Silverado 2500HD / 35002004.5–2006
GMC Sierra 2500HD / 35002004.5–2006

LLY Duramax problems and what to check

Overheating when towing (2004.5–2006)

Moderate

The LLY has the smallest radiator of any Duramax plus an EGR cooler adding heat, and its restrictive turbo inlet raises drive pressure. Under sustained towing, owners report high coolant temperatures, often made worse by a weak fan clutch, a failing water pump or a clogged cooling stack.[1]

Symptoms

  • Coolant temperature climbing on grades while towing
  • Fan not engaging strongly when hot
  • Coolant loss

Check before buying

  • Inspect the radiator and intercooler stack for debris
  • Check the fan clutch and water pump for play or leaks
  • Ask whether the truck has towed heavy loads regularly

Head gasket failure (2004.5–2006)

Major repair

Higher drive pressure and heat from the larger turbo working against a restrictive inlet are linked to blown head gaskets as LLY engines age.[1]

Symptoms

  • Coolant loss with no visible leak
  • Pressurized coolant reservoir
  • White exhaust smoke

Check before buying

  • Pressure-test the cooling system
  • Check for combustion gases in the coolant

Injector and injector-harness wear (2004.5–2006)

Moderate

LLY injectors fare better than the LB7's, but poor fuel quality or air in the fuel can cause failures as early as about 125,000 miles. The injector harnesses can also chafe from vibration and set injector circuit codes.[1]

Symptoms

  • Misfire or rough running
  • Injector circuit trouble codes

Check before buying

  • Scan for injector circuit codes
  • Ask for fuel-filter service history

Related GM research

Confirm a vehicle really has the LLY Duramax.

Engine and transmission RPO codes are recorded against the VIN. The CarWhere build sheet decodes a Chevrolet VIN into the factory-ordered option codes on record — engine, transmission, axle and packages. $9.99, instant.

Chevrolet build sheet by VIN

Frequently asked questions

What years is the LLY Duramax?

The LLY was used from midway through the 2004 model year through 2006 in Silverado and Sierra HD pickups. The LBZ replaced it during the 2006 model year.

How do I tell an LLY from an LB7 or LBZ?

LLY trucks carry a 2 as the 8th VIN digit, versus 1 for the LB7 and D for the LBZ. The RPO label in the glovebox also lists LLY.

How much horsepower does the LLY have?

The LLY is rated 310 hp at 3,000 rpm. Torque was 520 lb-ft at launch and 605 lb-ft for 2006.

Why do LLY Duramax engines overheat?

It has the smallest Duramax radiator plus an EGR cooler and a restrictive turbo inlet, so long towing climbs push temperatures up, especially if the fan clutch, water pump or radiator is worn or clogged.

Does the LLY have a DPF?

No. The LLY uses EGR and a catalytic converter, but the diesel particulate filter did not arrive until the LMM in 2007.5.

Sources

Ratings are GM-published figures as cited; descriptions are CarWhere’s own summaries of the sources below. Repair costs appear only where a source states them and vary by shop and region.

  1. Duramax History, Lesson 2: LLY — Drivingline
  2. Duramax V8 engine — Wikipedia (secondary reference)
  3. A Brief History Of Duramax Engine Specs — Diesel Army
  4. Duramax History, Lesson 3: LBZ — Drivingline
  5. 6.6L Duramax Diesel VIN ID Chart — DieselHub (secondary reference)

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Independent reference compiled by CarWhere — not affiliated with or endorsed by General Motors. Chevrolet, GMC, Cadillac, Corvette, Duramax, Vortec and the model names are trademarks of their owner.