2009 GMC SIERRA 3500HD

Typical onset: 150,000-250,000 mi

Symptoms: Heavy white or blue smoke on cold start, Coolant loss with no visible leaks, Excessive blow-by from crankcase, Metallic knocking noise that worsens under load, Fuel dilution in oil

Fix: LMM pistons can crack at the bowl rim, especially on tuned or hard-worked trucks. Requires complete engine rebuild or short block replacement. 40-60 hours labor for in-frame overhaul, more if pulling the engine. New pistons, rings, bearings, head gasket set, ARP studs recommended.

Estimated cost: $8,000-15,000

Typical onset: 100,000-180,000 mi

Symptoms: Hard starting or extended cranking, Rough idle with black smoke, Loss of power and poor fuel economy, Balance rates outside +/- 4 on scan tool, Check engine light with P0087 low fuel pressure codes

Fix: LMM injectors fail internally, often dumping fuel into cylinders and washing down cylinder walls (accelerating piston failures). Replace all 8 injectors as a set with updated versions, flush fuel system, change oil immediately. 8-12 hours labor. Do NOT replace just one.

Estimated cost: $4,500-6,500

Typical onset: 80,000-150,000 mi

Symptoms: Frequent regen cycles reducing fuel economy by 2-3 mpg, Derated power or limp mode, Check engine light with P2463 or P244B codes, Excessive exhaust backpressure, Black smoke during attempted regen

Fix: 2009 was first year for DPF on these trucks—system is crude. Clogged DPF requires replacement or professional cleaning. If regen system fails, also address dosing injector and pressure sensors. 4-6 hours labor for DPF replacement. Short trips and idling accelerate clogging.

Estimated cost: $2,000-3,500

Typical onset: 60,000-120,000 mi

Symptoms: Transmission fluid in coolant (strawberry milkshake in overflow), Coolant in transmission (burnt fluid, slipping), Leaking from cooler lines at crimp fittings, Harsh or delayed shifts after coolant contamination

Fix: The internal cooler in the radiator fails, allowing coolant and ATF to mix—catastrophic for the Allison. Requires radiator replacement, transmission flush or rebuild if contaminated, new cooler lines. If caught early (external leak only), 3-4 hours. If trans is contaminated, add 12-18 hours for rebuild.

Estimated cost: $800-1,200 (leak only), $4,000-6,000 (with trans damage)

Typical onset: 120,000-200,000 mi

Symptoms: No-start condition, Low fuel rail pressure codes, Metal shavings in fuel filter, Fuel system cuts out under heavy load, Long crank times

Fix: When the CP3 fails, it sends metal through the entire fuel system. Requires pump replacement, new injectors, fuel filter housing, flush all lines. Contaminated fuel rail must be cleaned. 10-14 hours labor. Always use quality fuel and change filters every 10k to prevent.

Estimated cost: $5,000-8,000

Typical onset: 90,000-150,000 mi

Symptoms: Coolant loss with no external leaks, White smoke from exhaust on startup, Steam from tailpipe, Overheating under load, Sweet smell from exhaust

Fix: EGR cooler develops cracks, pushing coolant into exhaust. Requires cooler replacement and full EGR system inspection. Many owners upgrade to aftermarket with better design. 5-7 hours labor. If ignored, coolant can flood cylinders and hydrolock the engine.

Estimated cost: $1,200-2,200

Typical onset: 80,000-140,000 mi

Symptoms: Clunking when shifting into drive or reverse, Vibration at highway speeds, Driveline shudder under acceleration, Visible sagging or torn rubber on mount

Fix: The transmission crossmember mount deteriorates from heat and weight, especially on trucks that tow. Simple replacement but requires supporting transmission. 1.5-2.5 hours labor.

Estimated cost: $250-450