2012 GMC SIERRA 3500HD

Typical onset: 100,000-180,000 mi

Symptoms: sudden loss of power and white smoke, metal shavings in fuel filter, hard starting or no-start, fuel in oil (dilution), multiple injector codes

Fix: When the CP4.2 pump grenades, metal debris contaminates the entire fuel system. Requires replacement of pump, all injectors, fuel rails, lines, tank cleaning or replacement, and sometimes the lift pump. 20-30 labor hours depending on contamination severity. This is the nightmare scenario for LML Duramax owners.

Estimated cost: $8,000-15,000

Typical onset: 120,000-200,000 mi

Symptoms: reduced power and limp mode, excessive regen cycles, poor fuel economy (3-5 mpg drop), check engine light with P2463 or P244B codes, black smoke during regen attempts

Fix: DPF becomes irreversibly clogged, especially on trucks used for short trips or low-load duty cycles. Cleaning rarely works long-term at this stage. Replacement DPF plus forced regen procedure. 4-6 hours labor.

Estimated cost: $2,800-4,200

Typical onset: 80,000-150,000 mi

Symptoms: DEF quality poor warning, speed limited to 55 mph, countdown to reduced power, P20E8 or P20BA codes, DEF tank heater failure in cold climates

Fix: DEF injector, pump, or tank heater/sender failures trigger limp mode. DEF system is intolerant of contamination or crystallization. Replacement of failed component plus system flush and software relearn. 3-5 hours labor depending on component.

Estimated cost: $1,200-2,800

Typical onset: 90,000-140,000 mi

Symptoms: transmission fluid puddles under truck, pink or red fluid stains on driveway, low transmission fluid level, transmission slipping or delayed engagement if fluid loss severe

Fix: The quick-connect fittings on the cooler lines crack or O-rings fail, especially at the radiator connection points. Common on trucks in salt states. Replace both lines as a pair with upgraded fittings. 2-3 hours labor.

Estimated cost: $400-700

Typical onset: 150,000-220,000 mi

Symptoms: coolant loss with no external leaks, white smoke from exhaust, P0401 insufficient EGR flow code, overheating under load, coolant in intake tract

Fix: EGR cooler develops internal leaks allowing coolant into exhaust or clogs with soot. Requires EGR cooler replacement and often EGR valve cleaning or replacement. 6-8 hours labor due to cab clearance issues.

Estimated cost: $1,800-3,200

Typical onset: 120,000-180,000 mi

Symptoms: rough idle and white smoke, single cylinder misfire code, fuel smell in oil, hard starting when cold, significant power loss

Fix: LML injectors can fail from normal wear, causing return rate issues or internal leaks. Diesel fuel dilutes engine oil. Single injector replacement requires cab removal or pulling engine forward. 8-10 hours labor, but smart money replaces all 8 if mileage is high.

Estimated cost: $1,200-2,000 per injector, $6,000-9,000 for all eight

Typical onset: 140,000-200,000 mi

Symptoms: P0299 underboost code, black smoke under acceleration, sluggish throttle response, limp mode activation, turbo whistle or grinding noise

Fix: Variable geometry turbo vanes stick from carbon buildup or actuator failure. Can sometimes be cleaned if caught early, but usually requires turbo replacement or rebuild. 6-8 hours labor.

Estimated cost: $1,500-3,500