2025 GMC Sierra 2500 HD Service and Repair Manual

Heavy-duty GMC buyers in 2025 choose from Pro, SLE, SLT, AT4, AT4X, Denali and Denali Ultimate, the last offered only with the diesel. Two engines cover the range: a 6.6L gasoline V8 that can also run on flex-fuel, and the 6.6L Duramax turbodiesel V8, each with an Allison ten-speed automatic. Regular, double and crew cabs carry over from the 2024 heavy-duty refresh. Because diesel emission hardware, cooling and towing systems differ sharply from the gas trucks, this factory service and repair manual keeps them separate, with procedures, torque values, wiring diagrams, diagnostics and maintenance schedules.

Engines covered

• 6.6L V8 — OHV, naturally aspirated, gasoline
• 6.6L V8 — OHV, naturally aspirated, flex-fuel
• 6.6L V8 — OHV, turbocharged, diesel

Body styles covered

• 4-door crew cab pickup
• 4-door extended cab pickup
• 2-door standard cab pickup

Trims covered

• AT4
• AT4X
• Denali
• Denali Ultimate
• Pro
• SLE
• SLT

Known issues on the 2025 Sierra 2500 HD. One recall is on federal record: trucks with the enhanced towing option and the 20-inch accessory wheel and tire package may carry a tire information label showing the wrong rear tire pressure, so the tires run underinflated and the monitoring system gives no warning. No owner complaints are recorded. This manual covers tire pressure specifications along with the relearn and diagnostic procedures for the tire pressure monitoring system.