2023 GMC Sierra 3500 HD Service and Repair Manual

This factory service and repair manual for the 2023 GMC Sierra 3500 HD deals with a single displacement in two very different forms: a 6.6L turbocharged diesel V8 of 403 cubic inches, and a 6.6L naturally aspirated V8 of 401 cubic inches burning gasoline or flex-fuel. Five trims are covered — AT4, Denali, Pro, SLE and SLT — over crew cab and extended cab pickups, a standard cab pickup, and cab and chassis units in four- and two-door form, each with its own specifications and diagnostics.

Engines covered

• 6.6L V8 (403 cu in) — OHV, turbocharged, diesel
• 6.6L V8 (401 cu in) — OHV, naturally aspirated, gasoline or flex-fuel

Body styles covered

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

Trims covered

• AT4
• Denali
• Pro
• SLE
• SLT

Known issues on the 2023 Sierra 3500 HD. One recall stands against this model year, and it concerns the power-unlatching tailgate: water reaching the gate-release switch can short it and let the tailgate open while the truck is under way, dropping unsecured cargo into traffic. Twenty-eight owner complaints are logged, half of them on the power train, with the electrical system and tires behind. The transmission and driveline procedures, body wiring diagrams and tailgate service steps in this manual are where those two threads meet.