2016 GMC Sierra 2500HD Problems: 7 Known Issues

On the 2011-2016 GMC Sierra 2500HD, the Bosch CP4.2 high-pressure fuel injection pump used on the 2011-2016 LML (and LGH) Duramax diesel engines is prone to catastrophic failure that destroys the entire fuel injection system. Unlike its predecessor the CP3, the CP4.2 uses roller tappets riding on the cam that are lubricated only by the diesel fuel; when the fuel film is thin or the fuel is aerated, the rollers skid instead of rolling and the cam and tappet wear. When metal fatigue occurs, the pump shatters and sends metal debris throughout the entire high-pressure fuel system — contaminating all eight injectors, the fuel rails, return lines, and feed lines. Total repair cost runs $8,000-18,000. A class action lawsuit (Chapman v. General Motors) was filed against GM over 2011-2016 Silverado/Sierra HD Duramax trucks and was settled for owners who bought in seven states (CA, FL, IL, IA, NY, PA, TX). The same pump also fails in the Ford 6.7 Power Stroke (2011+) and the 2019-2020 Ram 6.7 Cummins.

On the 2011-2016 GMC Sierra 2500HD 6.6L Duramax LML, the LML Duramax EGR (exhaust gas recirculation) cooler is prone to coolant leaks internally, allowing coolant to enter the intake manifold and combustion chambers. Coolant in the intake causes white smoke, rough running, and potential hydrolocking of cylinders. The EGR valve also sticks open or closed from carbon buildup, causing rough idle, black smoke, and check engine lights. The EGR cooler failure can occur as early as 60,000 miles on trucks used in stop-and-go driving. GM bulletin 08-06-04-003D provides the EN-48974 adapter set for pressure-testing the EGR cooler for coolant leaks into the combustion chambers.

On the 2006-2016 GMC Sierra 2500HD, the Garrett variable-geometry turbocharger used on the LBZ, LMM and LML Duramax controls boost by pivoting vanes on a unison ring inside the turbine housing. Soot and carbon bake onto the ring over time and it begins to bind, so the actuator can no longer move the vanes to the commanded position. The ECM sees the mismatch and sets P003A (turbocharger position performance) and/or P2563 (turbocharger vane position sensor performance), usually together, and puts the truck in a reduced-power state. Trucks that idle a lot or run short trips soot the ring up fastest. Duramax forum and Diesel Place threads on these two codes run for hundreds of pages across 2006-2016 Sierra 2500HD trucks.

On the 2011-2019 GMC Sierra 2500HD, the Allison 1000 6-speed automatic transmission used behind the Duramax diesel in Sierra 2500HD/3500HD is widely regarded as extremely durable, but the Transmission Control Module (TCM) and solenoid pack do develop faults. Common issues include harsh 1-2 shifts, transmission sticking in one gear, slip codes, and the truck going into limp mode (3rd gear only). Using the wrong fluid or skipping fluid service is a common cause of premature solenoid wear. TCM software updates from GM address most calibration-related shift complaints.

On the 2015-2016, 2018-2019 GMC Sierra 2500HD, the side-curtain (roof-rail) air bag inflators fitted to certain 2015-2016 and 2018-2019 Sierra 2500HD cabs can have the inflator end cap detach during deployment, releasing compressed gas into the headliner and propelling the cap and headliner components into the occupant compartment. GM has issued a repeating series of NHTSA recalls covering this defect as the affected production population has been refined: 20V736000 and 21V504000 for 2015-2016 trucks, then 24V756000, 25V432000, 26V166000 and 26V325000 reaching 2018-2019 Sierra 2500HD Crew Cabs. Because a defective inflator can injure the very occupant the bag is meant to protect, NHTSA classes this as a serious safety defect rather than a nuisance.

On the 2011-2016 GMC Sierra 2500HD 6.6L Duramax V8 (RPO LML), the 2011-2016 6.6L Duramax RPO LML added selective catalytic reduction, and the aftertreatment hardware is the engine's most frequent expense. The DEF tank heater and level/quality sender assembly fails often, the DEF (reductant) injector crystallizes and clogs, and pre-2015 NOx sensors drift out of calibration and report false "DEF quality poor" faults. Because these are emissions-critical, the truck gives a countdown of remaining miles and then enforces a hard speed limit - 55 mph then 4 mph - regardless of whether the DEF fluid is actually bad. Owners on duramaxforum.com and silveradosierra.com report P20EE, P249D and P22FE as the recurring set. This is LML-specific; the LMM has no DEF system.

On the 2011-2023 GMC Sierra 2500HD, sierra 2500HD 4WD trucks use a front axle disconnect system with an electric actuator on the front axle. The actuator motor and position sensor commonly fail between 80,000-120,000 miles, causing the 4WD system to not engage, to partially engage (binding and vibration), or to throw a 4WD Service warning. Heavy-duty truck use — particularly towing and off-road — accelerates actuator wear. On 2019-2022 trucks, GM bulletin 20-NA-209 traces Service 4WD messages with DTCs C118D, C119B or C119C to water intrusion and corrosion in the front axle actuator connector and harness terminals.