Problems With a Duramax LLY

by Roger Shao
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First introduced in 2004, the Duramax LLY engine is a 32-valve turbocharged diesel engine made popular by the Hummer H1, Chevy Silverado and GMC Sierra. Upgrades over previous years included a Garret turbocharger that allowed General Motors to meet new diesel truck emission standards while maintaining the original power-to-weight ratio. While powerful, the turbocharger has caused several issues vehicle owners have discovered through extended use.

Turbocharger Inlet Mouthpiece

The most common issues LLY owners encounter include decreased fuel mileage, overheating and poor turbo response. These symptoms result from the inlet mouthpiece of the Garrett turbocharger having to fit into a smaller engine space. The redesigned mouthpiece includes a sharp ridge that causes restricted and turbulent airflow and severely taxes the compressor. With time, the turbocharger will become less responsive, resulting in decreased fuel mileage.

Drive belt chirp

Another issue commonly encountered by LLY owners is a squeak or chirping noise heard from the engine's drive belt as the driver shuts off the truck. Some owners also hear the noise during starts and occasionally during operation. To solve the issue, replace the belt with a new GM accessory drive belt.

Fuel Injectors

The LLY's previous incarnation in the Duramax family of engines, the LB7,came about in 2001. A known defect of the LB7 engine centered on its propensity for fuel injector failure that led GM to extend the engine's warranty to seven years/200,000 miles. To ward off similar problems on the LLY, GM changed the valve covers to allow easy injector replacement. This modification has not prevented issues of fuel leakage and other issues, however.


Heavy-duty engines such as the Duramax LLY often have to tow heavy loads across long distances. In situations such as hot weather or steep inclines, the LLY has been known to overheat. To compensate for the increased thermal output in these situations, the installation of a secondary cooling fan might do the job.

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