2009 GMC Sierra 2500HD Problems: 4 Known Issues

On the 2007-2010 GMC Sierra 2500HD 6.6L Duramax V8 (RPO LMM), the 2007.5-2010 6.6L Duramax RPO LMM was GM's first Duramax with a diesel particulate filter, and the early calibration regenerates far too often. Owners on duramaxforum.com and dieselplace.com report the truck entering regen every 100-200 miles, and in trucks used for short trips, heavy idling or slow towing the regen cycle is repeatedly interrupted before completion. Soot then accumulates faster than it burns off, the differential pressure across the filter climbs, and the truck eventually refuses to self-regen at all and derates. The excess fuel injected late in the cycle for regeneration also washes down the cylinder walls and dilutes engine oil. This is an LMM-specific pattern; the pre-2007.5 LBZ has no DPF, and the LML added SCR/DEF which changed the regen strategy.

On the 2003-2013 GMC Sierra 2500HD, gMT800 and early GMT900 Sierra 2500HD instrument clusters use tiny stepper motors to drive each needle, and those motors fail as a matter of course. The speedometer sticks, reads wildly wrong or flutters; the fuel, temperature, oil pressure and voltmeter needles drop dead or sit at false values. On a diesel HD truck the loss of the coolant temperature and oil pressure gauges is genuinely dangerous because the driver loses the early warning of an overheat. GM acknowledged the condition and ran Special Coverage Adjustment 07187C, extending coverage to 7 years/70,000 miles - that program has long since expired while the failures continue.

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 2001-2014 GMC Sierra 2500HD, the electric-shift NV246/NV263 transfer case on Sierra 2500HD trucks is positioned by an encoder motor mounted to the case, with a sensor ring inside it reporting shaft position back to the Transfer Case Control Module. Moisture and road salt corrode the encoder motor and its sensor ring, and the dash selector switch itself develops open contacts. When the TCCM loses a valid position signal it illuminates "Service 4WD" and refuses to shift. The classic pattern owners describe is a truck that will still drop into 4LO but will not engage 4HI, because the module can drive the case to its travel extremes but cannot stop it at the intermediate position. C0327 is the code that identifies it.