BUY WITH CARE

The LB7 Duramax's defining defect is its fuel injectors. On the 2001-2004 6.6L diesel, the Bosch injectors crack or erode internally (owners and a GM owner-notification letter quoted in the complaint texts describe injector body cracks, ball-seat erosion, and high fuel return), and the failures recur -- one owner reports replacing injectors four times. Because the LB7's injectors sit under the valve covers, replacing all eight is a labor-heavy, expensive engine-top job, and GM's special coverage for it has long since expired. Worse, a failed injector can dump diesel past the rings into the crankcase, over-filling the oil and diluting it; several complaint texts describe fuel mixing with the oil and, in the worst cases, the engine seizing. The truck also tends to simply shut down when an injector fault trips.

Check — On any LB7, ask whether the injectors have been replaced and when, and treat original high-mileage injectors as a large pending expense. Check the oil level and smell for diesel dilution (an over-full, thin, fuel-smelling dipstick is a red flag), watch for hard starting, rough running, knock, excessive white smoke, and a rising oil level between changes.