2017 GMC SIERRA 3500HD

Typical onset: 80,000-150,000 mi

Symptoms: sudden loss of power, metal shavings in fuel system, hard starting or no-start, fuel in oil, entire fuel system contaminated

Fix: When the CP4.2 grenades internally, metal debris contaminates the entire fuel system—tanks, lines, injectors, lift pump, rails. Full fuel system flush/replacement plus all eight injectors, both fuel rails, lines, and pump. 20-30 hours labor depending on contamination severity. Many owners install CP3 conversion kit during repair to prevent recurrence.

Estimated cost: $8,000-15,000

Typical onset: 60,000-120,000 mi

Symptoms: reduced engine power message, check engine light with P20EE (SCR efficiency), DEF quality/heater codes, frequent active regens, poor fuel economy from incomplete regens

Fix: DEF injector clogs or fails, DEF heater grid shorts, or EGR cooler clogs causing regen problems. DEF injector replacement runs 2-3 hours, EGR cooler is 6-8 hours due to turbo removal. Diagnostic time critical—don't just throw parts. Short-trip driving accelerates issues.

Estimated cost: $800-3,500

Typical onset: 70,000-130,000 mi

Symptoms: transmission fluid spots under truck, fluid level dropping, cooler lines wet at frame rail connections, pink residue on frame, transmission overheating if severe

Fix: Factory quick-connect fittings on cooler lines corrode and leak where they meet the frame-mounted cooler. Both lines typically need replacement as plastic quick-connects become brittle. 2-3 hours labor, often caught during oil changes. Aftermarket braided line upgrades available.

Estimated cost: $400-800

Typical onset: 80,000-140,000 mi

Symptoms: clunk when shifting into drive/reverse, excessive vibration at idle, visible engine movement when revving, driveline shudder under load, transmission shifter feels loose

Fix: Diesel torque and weight tears rubber mounts, especially on trucks used for towing. Transmission mount is 1.5 hours, engine mounts 2-3 hours. All three typically done together for efficiency. Heavy towing accelerates wear significantly.

Estimated cost: $600-1,200

Typical onset: 100,000-180,000 mi

Symptoms: P0087 low fuel rail pressure, black smoke under acceleration, limp mode activation, turbo underboost codes, sluggish throttle response

Fix: Variable-geometry turbo actuator sticks from carbon buildup or actuator motor fails. Can sometimes clean and free up (3-4 hours), but often needs new actuator assembly (5-6 hours) or entire turbo if vanes seized. Tuned trucks see this earlier.

Estimated cost: $1,200-3,800

Typical onset: 120,000-200,000 mi

Symptoms: rough idle when cold, white smoke at startup, fuel dilution in oil, balance rate codes, hard starting, cylinder contribution faults

Fix: Piezo injectors leak internally or fail electrically. One bad injector often indicates others are marginal. Balance rates diagnose which cylinder. Single injector 2 hours, but most techs recommend doing multiple or all eight if mileage is high. Return rate testing critical.

Estimated cost: $800-6,500

Typical onset: 80,000-150,000 mi

Symptoms: clunk when accelerating from stop, vibration at highway speed, squeaking during turns, clicking under load, visible play in driveshaft

Fix: Heavy-duty use and torque wear U-joints and center carrier bearing. Front and rear driveshaft U-joints need replacement or full driveshaft if seized. 2-4 hours depending on how many joints and carrier bearing condition. Check carefully during every alignment.

Estimated cost: $500-1,400