Used Duramax LML (2011-2016): what to check before you buy

1Before you go

Run the VIN and ask for the paperwork on the campaigns below: a done recall or program is a solved problem, an open one is a free repair the seller has not had done.

• Run the VIN

  It confirms the engine and lists the campaigns for that model year. Whether a recall is still open on this VIN: nhtsa.gov/recalls.

• Programs, extended coverages and emissions recalls
  • Special Coverage 29400 · Special coverage / warranty extension · 2013-2015 Silverado/Sierra HD
  • Special Coverage 14652 · Special coverage / warranty extension · 2011-2012 Silverado/Sierra HD (2010-2012 Express/Savana)
  • Special Coverage 14653 · Special coverage / warranty extension · 2011-2014 Silverado/Sierra HD
  • Special Coverage 15457 · Special coverage / warranty extension · 2011-2015 Silverado/Sierra HD

  Plus 5 service bulletins on the recalls page.

2Cold start and idle

Ask the seller not to start or warm the engine before you arrive. Most of these only show on a cold engine; then let it idle and listen.

• Bosch CP4.2 high-pressure pump failure and fuel-system contamination
  • sudden loss of power / rough running, then a no-start as rail pressure collapses
• Glow plug / control module cold-start service (LML)
  • hard starts only when cold; glow-plug circuit codes (often bank-specific)
• Piezo injector failures / replacement economics (LML)
  • injector balance/contribution codes, rough idle, fuel dilution of oil
  • hard starting after sitting; one-cylinder miss under load

3Scan for codes

A basic OBD-II reader shows stored and pending codes; on a diesel ask a shop for a full scan if you can. These are the codes our records tie to known failures on this engine.

What a code means on each engine: trouble codes by engine.

4Hood up and underneath

Engine off, in daylight, with a flashlight.

• Bosch CP4.2 high-pressure pump failure and fuel-system contamination
  • metal shavings in the fuel filter housing; the CP4's internal cam/c-roller wears through and sends debris down the high-pressure lines into the rails and injectors

  To confirm: cut open the fuel filter first: metal particles = CP4 cascade, stop cranking

• DEF system failures: tank heater, dosing, quality (LML)
  • crystallized DEF at the doser; heater circuit faults in cold weather

  To confirm: read the specific DEF DTC family and test the heater circuit for an open before replacing the tank

• Cooling system wear: water pump, fan clutch, oil cooler (LML)
  • coolant seepage at the water pump weep hole; bearing growl

  To confirm: pressure-test the system; verify thermostat and fan clutch operation under load before radiator replacement

• EGR valve / cooler carbon and coolant service (LML)
  • coolant loss traceable to the EGR cooler; carbon buildup at the valve

  To confirm: command the EGR valve with a bidirectional tool before replacing it

5Test drive

At least 20 minutes, including a highway run and a hill or a load if you can.

• DEF system failures: tank heater, dosing, quality (LML)
  • 'Service DEF System - See Dealer' with a countdown to a speed-limited mode
  • repeated DEF-related codes; tank/level-sensor assembly replacements
• VGT turbo vane carbon / actuator wear (Garrett VVT)
  • underboost codes (P0299), limp mode under load, whistling/whoosh changes
  • gradual power loss traced to stuck VGT vanes (carbon) or a worn actuator
• Cooling system wear: water pump, fan clutch, oil cooler (LML)
  • overheating under tow traced to a locked/loose fan clutch
• DPF regeneration service (retained system)
  • frequent regens, derate warnings on short-trip duty
• EGR valve / cooler carbon and coolant service (LML)
  • EGR flow codes, hesitation under load
• NOx sensor failures (LML SCR system)
  • check-engine light with NOx circuit codes; DEF/SCR system warnings
  • failed emissions readiness after sensor replacement without calibration

What it costs if you find it

Parts budgets from our repair recipes for this engine: Dave's Auto Center's prices where Dave's lists the part, approximate OEM and maker catalog prices (rounded) for the rest; labor not included. A campaign listed next to a failure may make the repair free on a covered truck: check it by VIN.