How do I tell if I have a LB7 or LLY Duramax Engine?
In 2004 GM switched the Duramax engine offered mid year from the LB7 to the LLY. To figure out what engine is in your vehicle simply reference the VIN number.
Early 2004 Duramax engine was the LB7 (8th VIN digit = '1')
Late 2004 or 2004.5 Duramax engine was the LLY (8th VIN digit = '2')