2018 GMC SIERRA 2500HD

Typical onset: 60,000-150,000 mi

Symptoms: Sudden loss of power and white smoke from exhaust, Metal shavings throughout entire fuel system, Hard starting or no-start after pump failure, Fuel contamination requires complete system flush

Fix: When the CP4.2 pump grenades, metal debris circulates through injectors, fuel rails, and lines. Requires replacement of pump, all eight injectors, fuel rails, lines, tank cleaning or replacement, and sometimes complete engine teardown if metal entered cylinders. 40-80 hours labor depending on contamination severity.

Estimated cost: $8,000-20,000

Typical onset: 80,000-120,000 mi

Symptoms: Transmission fluid puddles under front of truck, Burnt transmission fluid smell, Low transmission fluid warnings, Leaking at crimped fittings or cooler itself

Fix: The Allison 1000 cooler lines corrode at crimp points and the cooler develops pinhole leaks. Requires replacement of hard lines and/or external cooler assembly. Lines alone are 3-4 hours; cooler adds another 2-3 hours if radiator must come out for access.

Estimated cost: $600-1,400

Typical onset: 70,000-110,000 mi

Symptoms: DEF system fault message with derate warning, Poor DEF quality or incorrect fluid detected message, Tank heater element failure in cold climates, Speed limited to 55 mph after countdown expires

Fix: DEF tank heater elements fail, allowing fluid to crystallize in lines and injector. Often requires tank replacement ($800-1,200 parts), DEF injector ($400-600), and sometimes NOx sensors. Tank R&R is 4-6 hours; injector adds 2-3 hours. Flush lines thoroughly.

Estimated cost: $1,500-3,000

Typical onset: 60,000-100,000 mi

Symptoms: Clunking when shifting from Park to Drive, Excessive driveline vibration under load, Visible cracking or separation of rubber mount, Transmission movement visible during throttle application

Fix: The Allison's weight and torque crack the transmission crossmember mount. Replacement is straightforward: support transmission, remove crossmember, install new mount and bushings. 1.5-2.5 hours including alignment check.

Estimated cost: $250-500

Typical onset: 100,000-150,000 mi

Symptoms: White smoke from exhaust under load, Coolant loss with no visible leaks, Rough idle and reduced power, Coolant in exhaust or exhaust gas in coolant

Fix: EGR cooler develops internal cracks, allowing coolant into exhaust stream or vice versa. Requires EGR cooler replacement and sometimes EGR valve cleaning. Cab must come up for proper access on this chassis. 8-12 hours with cab removal, EGR cooler ($800-1,200 parts).

Estimated cost: $2,500-4,000

Typical onset: 90,000-140,000 mi

Symptoms: P0299 or P0046 turbo underboost/overboost codes, Black smoke under acceleration, Lack of power especially when towing, Audible grinding or squealing from turbo area

Fix: Carbon buildup on variable vane mechanism causes sticking, reducing boost control. Can sometimes be cleaned in place with specialized solvents (3-4 hours), but often requires turbo removal, disassembly, and cleaning or actuator replacement (6-9 hours). Complete turbo replacement if bearing damage present.

Estimated cost: $1,200-3,500

Symptoms: Extended cranking before starting, especially cold, Intermittent loss of prime requiring repriming, Air bubbles visible in clear fuel filter housing, Rough idle that clears after running a few minutes

Fix: The fuel filter housing develops cracks or O-ring seals fail, allowing air into the low-pressure side. Requires housing replacement or seal kit installation with thorough priming procedure. 1.5-2.5 hours including bleeding system. Sometimes multiple components leak simultaneously.

Estimated cost: $300-700