GM Duramax 6.6L LMM: Specs, Engine Codes, Controllers & Maintenance

Engine Information · GM · Duramax · LMM

Duramax 6.6L LMM

The LMM combines the 6.6L Duramax’s towing torque with a diesel particulate filter. Pickup and commercial-van calibrations differ substantially, so a shared engine code does not mean a shared power rating or tune file.

USA & CanadaLMM HD pickup / LMM vanSpecs · Controllers · Maintenance

Duramax turbo-diesel cutaway — family reference; exact RPO unconfirmed. Photo by Aaron & Alli. Resized and framed for web. CC BY 2.0.

Engine construction

Specification	Details
Capacity / layout	6,604 cc · 90° V8
Bore × stroke	103 × 99 mm
Construction	Cast-iron block · aluminum heads
Valve gear	OHV · 32 valves
Fuel / induction	Common-rail direct injection · variable-geometry turbo
Compression	16.8:1

Codes & output

RPO / version	Power / torque	Key difference
LMM HD pickup	365 hp / 660 lb-ft	Pickup rating
LMM van	250 hp / 460 lb-ft	Commercial rating

SAE horsepower; torque in lb-ft. Ratings are for the stated application and fuel, rather than every vehicle with this RPO.

Vehicles & model years

Brand	Model	Model years	Platform / chassis	Engine RPO
GMC / Chevrolet	Sierra / Silverado HD	2007.5–2010	GMT900	LMM
GMC / Chevrolet	Savana / Express	2008–2010; confirm build/RPO	GMT610	LMM

U.S. and Canadian applications within the 2005–2026 matrix scope. Engine availability depends on trim, build date and emissions certification.

Engine controllers

Application / revision	ECM or PCM	Identification & function
LMM	Bosch E35B ECM	Adds DPF regeneration and soot-loading functions to injection, EGR and turbo control
Transmission	Allison A40/A50 or van-specific TCM	Pickup and van transmissions require their own calibration; read the module ID

Identify the module from its service number, operating-system ID and VIN. The ECM/PCM and transmission controller have separate calibrations on many applications; a matching RPO alone does not make a replacement module plug-and-play.

Common issues & maintenance

Fuel supply / hard startingAir leaks at the filter housing, restricted filters and excessive injector return flow can prevent rail pressure from reaching the starting target. Test supply vacuum and return flow rather than diagnosing from injector balance rates alone.
Turbo-vane controlSticking vanes, position-sensor faults and charge-air leaks can produce low boost or reduced power. Compare commanded and actual vane position and inspect hoses before replacing the turbo.
DPF regeneration problemsShort-trip use, failed pressure/temperature sensors and underlying fuel or air faults can interrupt regeneration. Establish the cause of excessive soot before forcing repeated regeneration.

Keep it healthy. Follow the VIN-specific oil and fuel-filter schedule, shortening service for towing, idling and repeated short trips where the manual requires it. Drain water from fuel when indicated, maintain the cooling stack and investigate falling rail pressure before replacing expensive fuel-system parts. Give normal regeneration a chance to finish and respond promptly to DPF warnings.

References & technical sources

Source	Reference
GM applications & RPO diagnostic matrices	View source
EFILive GM diesel controller families	View source
EFILive GM Diesel controller guide	View source
Fuel-system diagnostic reference	View source
GM Duramax output and identification bulletin	View source