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How to Identify Your Duramax Diesel Engine Code

For the 2001 model year, General Motors finally replaced the Detroit Diesel 6.2L and 6.5L turbodiesel V8’s they had been using for 20 years, with a new 6.6L V8 developed in-house with Isuzu’s heavy truck division. The new engine was much more powerful than before, being developed from the beginning for turbocharging, and using Bosch common-rail injection with a CP3 injection pump for more precise fuel control. Coming out right when American consumers started switching from cars to trucks, it was a huge success; the engine factory in Ohio produced the millionth Duramax diesel less than 7 years after the first.

Like most diesel pickups, the Duramax has a reputation for durability and longevity. Still, with the miles and work these trucks see, it’s inevitable that some repairs can eventually come up. Ordering the correct replacement parts can be a little more difficult; while Ford has a new engine every few years (7.3 to 6.0 to 6.4 to 6.7L PowerStroke), General Motors has kept using derivatives of the same 6.6L casting, providing incremental updates along the way.

Each revision of the Duramax is assigned a new 3-digit RPO code, which is GM’s internal designation for a particular option. Your truck may have a Z71 sticker on the side of the bed indicating an off-road package; that is an example of an RPO code. Other famous ones include the Camaro Z28 or Corvette Z06. Because multiple versions of the Duramax were available in some years, knowing the engine code of your Chevy Silverado or GMC Sierra will make it much easier to ensure you get the correct parts the first time. You can either look it up by application or check the 8th digit of your truck’s VIN to confirm. Duramax Diesel engine RPO codes include:

 

LB7

VIN Digit: 1

Applications: 2001-Early 2004 Chevy Silverado and GMC Sierra, 2001-2005 Chevy Kodiak and GMC TopKick

Details: First version of the Duramax diesel. Known for fuel injectors leaking into the oil supply; see TSB #04039B. Also need to keep an eye on coolant temperatures and be proactive about cooling system repairs at risk of premature head gasket failure.

Single LB7 injector available here

Complete set of LB7 injectors (with seals and glow plugs) available here

49-State LB7 turbo available here

California emissions compliant LB7 turbo available here

LB7 diesel injection pump available here

LB7 fuel injection control module (FICM) available here

LLY

VIN Digit: 2

Applications: Late 2004 (2004.5) and 2005 Silverado, 2006 Hummer H1 Alpha

Details: First revision to the Duramax. Includes a variable geometry turbocharger; this means there are airflow vanes inside the turbo that can simulate a smaller turbo at low RPM (for faster spooling and less lag), then open up at higher RPM (for higher boost and more top-end power). Valve covers are redesigned to make it easier to replace injectors. First Duramax to use an EGR (exhaust gas recirculation) system.

Single LLY injector available here

Complete set of LLY injectors (with seals and glow plugs) available here

LLY turbo available here

LLY diesel injection pump available here

LLY fuel injection control module (FICM) available here

LBZ

VIN Digit: D

Applications: 2006 Silverado, Sierra, Kodiak and TopKick, 2007 Silverado and Sierra Classic (older GMT800 body style, NOT the newer GMT900), 2006 Chevy Express and GMC Savana full-size vans (first year of the vans offering the Duramax as an option)

Details: Often regarded by diesel enthusiasts as the best version of the Duramax. This version has stronger rods and engine block than the earlier LB7 and LLY trucks, without the emissions equipment of the newer LMM.

Single LBZ injector available here

Complete set of LBZ injectors (with seals and glow plugs) available here

LBZ turbo available here

LBZ diesel injection pump available here

LMM

VIN Digit: 6 for 2500/3500 pickups and vans, 9 for 4500/5500 Cab and Chassis Silverado, Sierra, TopKick or Kodiak

Applications: 2007-2010 Silverado, Sierra, Kodiak, TopKick, Express and Savana

Details: This engine was released with the all-new GMT900-chassis 2007 Silverado and Sierra. It features more emissions controls than any previous Duramax diesel V8, including a Diesel Particulate Filter (DPF).

Single LMM injector available here

Complete set of LMM injectors (with seals and glow plugs) available here

LMM turbo available here

LMM diesel injection pump available here

LML

VIN Digit: 8

Applications: 2011-2016 Chevrolet Silverado and GMC Sierra pickups

Details: Has a revised fuel system and programming to better comply with new emissions requirements, and better compatibility with biodiesel. Also has a urea-injection system (also known as diesel exhaust fluid, or DEF) for better emissions performance.

Single LML injector available here

Complete set of LML injectors available here

LML turbo available here

LML diesel injection pump available here

LGH

VIN Digit: L

Applications: Late 2010 (2010.5)-2016 Chevy Express and GMC Savana vans, 2011 Silverado and Sierra 4500/5500 cab and chassis (no pickup bed)

Details: Variant of the LML with different emissions programming, because the vans and cab/chassis trucks have different emissions requirements than the pickups.

Single LGH injector available here

Complete set of LGH injectors available here

LGH turbo available here

LGH diesel injection pump available here

L5P

VIN Digit: Y

Applications: 2017 and newer Silverado and Sierra

Details: Newest version of the Duramax; similar-but-not-identical hardware to the LML, with a different turbo and tune. 445 horsepower, 910 lb-ft of torque. This revision was intended to remain competitive with Ford PowerStroke and Ram Cummins diesel pickups.

L5P turbo available here

If you’re still unsure about what’s best for your vehicle, feel free to contact BuyAutoParts for knowledgeable assistance in getting the best replacement diesel parts for your vehicle. We carry guaranteed exact fit turbos, injectors, fuel pumps and more from known brands like Bosch, Garrett, Delphi, Stigan and more. All our parts professionals are here and ready to help!

Model 8th VIN Digit RPO Code
Chevy Express or GMC Savana Van D LBZ
Chevy Express or GMC Savana Van 6 LMM
Chevy Express or GMC Savana Van L LGH
Chevy Kodiak or GMC TopKick 1 LB7
Chevy Kodiak or GMC TopKick D LBZ
Chevy Kodiak or GMC TopKick 9 LMM
Chevy Silverado or GMC Sierra 1 LB7
Chevy Silverado or GMC Sierra 2 LLY
Chevy Silverado or GMC Sierra D LBZ
Chevy Silverado or GMC Sierra 6 LMM
Chevy Silverado or GMC Sierra 9 LMM
Chevy Silverado or GMC Sierra L LGH
Chevy Silverado or GMC Sierra 8 LML
Chevy Silverado or GMC Sierra Y L5P
Hummer H1 Alpha 2 LLY

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