2021 GMC Sierra 2500 HD Service and Repair Manual

This factory service and repair manual for the 2021 GMC Sierra 2500 HD adds flex fuel to the gasoline V8's description, so the 6.6L overhead-valve V8 of 401 cubic inches runs gasoline or flex fuel and the 6.6L turbocharged diesel V8 of 403 cubic inches remains the working alternative. Bodies are a 4-door crew cab pickup, a 2-door standard cab pickup and a 4-door extended cab pickup, in Base, AT4, Denali, SLE or SLT trim. Procedures, specifications, torque values, wiring diagrams and diagnostics are given for each engine and body.

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

Trims covered

• Base
• AT4
• Denali
• SLE
• SLT

Known issues on the 2021 Sierra 2500 HD. Six recalls appear on the federal record. One covers brake pressure modulator valve bolts left loose during assembly, so the two halves may not seal and water can get in and short the circuit. Another covers a transmission control valve that can fail and lock the rear wheels. Two more cover seat belts: brackets not secured to the front-row center seat frame, and wrong bolts at fastening points. A tailgate release switch that shorts on water intrusion and a spare tire mismatch that defeats antilock control complete the list. Owners filed 51 complaints, mostly on the power train.