The Duramax engine has evolved from the original LB7 series to the LLY, LBZ, LMM and then the LML series.
The LB7 was used from 2001 model year until mid 2004 model year.
In mid 2004 the LLY series was released.
In mid 2006 the Duramax changed again. The early 2006 engines were still called LLY and the later 2006 and 2007 “Classic” became the LBZ. This creates some confusion as the 06 LLY is distinctively different from the 04.5-05 LLY.
The 2006 LLY and LBZ engines are essentially the same.
The LMM began in the new body style GMT 900 series trucks in 2007, and was replaced in the 2011 model year with the current LML. The simplest way to verify which series you have is the VIN# of the truck.
The 8th digit is the engine ID and it will either be a 1, 2, D, 6 or 8.
• 01-04.5 LB7 is a 1
• 04.5-05 LLY is a 2
• 06 LLY is a 2 (uses same injectors as LBZ)
• 06-07 LBZ is a D
• 07-10 LMM is a 6 (new body style GMT 900 series)
• 11+ LML is an 8
Example: 1GCHK29143EXXXXXX for LB7 and 1GCHK29245EXXXXX for LLY. It is important to note that as while the engines are essentially the same at the core, the electronics, turbochargers, electronics, and injectors are different among the variants. The 10th place in the VIN number identifies the model year on these vehicles. The example above shows the 2003 model year LB7 and 2005 LLY.