2021 GMC Sierra 3500 HD

The 2021 GMC Sierra 3500 HD is a heavy-duty pickup truck known for its towing and hauling capabilities. Engine options include the 6.6L L8T V8 gasoline engine producing 401 horsepower and 464 lb-ft of torque and the 6.6L Duramax L5P turbodiesel V8 engine producing 445 horsepower and 910 lb-ft of torque. The gasoline engine is paired with a 6-speed automatic transmission, while the diesel engine is paired with a 10-speed Allison automatic transmission. Owners generally appreciate the Sierra 3500 HD’s powerful engine options, comfortable interior, and advanced technology features. Common dislikes include the truck’s large size, which can make it difficult to maneuver in tight spaces, and some reports of reliability issues.

Engine

6.6L L8T V8 Gasoline

• No Issues Found

6.6L Duramax L5P Turbodiesel V8

• Fuel Injector Failure
  • Description/Symptoms: Rough running, misfires, decreased fuel economy, and the smell of diesel fuel in the exhaust. In severe cases, engine damage can occur.
  • Solution: Replacement of the faulty fuel injector(s). It’s recommended to replace all injectors if one fails due to the potential for other injectors to fail soon after.
  • Estimated Cost to Fix: $800 - $1200+ per injector.
  • Recalls: None Found
• CP4 High-Pressure Fuel Pump Failure
  • Description/Symptoms: Engine stalling, no-start condition, metallic debris in the fuel system, and potential for widespread fuel system damage.
  • Solution: Replacement of the CP4 pump and potentially other fuel system components. A CP3 conversion is a popular, more reliable alternative.
  • Estimated Cost to Fix: $3000 - $10,000+ depending on the extent of the damage and parts used.
  • Recalls: None Found

Transmission

6-Speed Automatic (Paired with 6.6L L8T)

• No Issues Found

10-Speed Allison Automatic (Paired with 6.6L Duramax L5P)

• Torque Converter Shudder
  • Description/Symptoms: A vibration or shudder felt during light acceleration, typically between 30-50 mph.
  • Solution: In some cases, a transmission fluid flush with updated fluid can resolve the issue. In more severe cases, torque converter replacement is necessary.
  • Estimated Cost to Fix: $300 - $500 for a fluid flush, $1500 - $3000+ for torque converter replacement.
  • Recalls: None Found
• Harsh or Delayed Shifts
  • Description/Symptoms: Hard or jerky shifts between gears, especially during acceleration or deceleration. Delayed engagement when shifting from Park to Drive or Reverse.
  • Solution: Software recalibration of the transmission control module (TCM) may resolve minor issues. Valve body replacement or complete transmission overhaul might be needed for more severe cases.
  • Estimated Cost to Fix: $100 - $300 for recalibration, $800 - $2000+ for valve body replacement, $3000 - $6000+ for transmission overhaul.
  • Recalls: None Found

Suspension

• No Issues Found

Electrical

• Infotainment System Glitches
  • Description/Symptoms: Freezing, screen blackouts, slow response times, Bluetooth connectivity issues, and Apple CarPlay/Android Auto malfunctions.
  • Solution: Software updates from the dealer, or infotainment system reset or replacement.
  • Estimated Cost to Fix: $0 - $200 for software updates (often covered under warranty), $500 - $1500+ for infotainment system replacement.
  • Recalls: None Found
• Sensor Failures (E.g., Blind Spot Monitoring, Parking Sensors)
  • Description/Symptoms: False alerts, non-functional sensors, and error messages on the driver information display.
  • Solution: Replacement of the faulty sensor.
  • Estimated Cost to Fix: $200 - $500+ per sensor depending on location and type.
  • Recalls: None Found

Exterior

• Cracked Tail Lights
  • Description/Symptoms: Cracks develop in the outer lens of the tail lights. Can lead to moisture ingress and further damage.
  • Solution: Replacement of the tail light assembly.
  • Estimated Cost to Fix: $200 - $400+ per tail light.
  • Recalls: None Found

Interior

• Heated/Cooled Seat Malfunction
  • Description/Symptoms: Seats either not heating/cooling at all, or providing inconsistent or inadequate heating/cooling.
  • Solution: Diagnosis of the heating/cooling element, blower motor, or control module. Replacement of the faulty component.
  • Estimated Cost to Fix: $200 - $800+ depending on the component replaced.
  • Recalls: None Found

Summary

The 2021 GMC Sierra 3500 HD has some potential issues to be aware of. The Duramax diesel engine may experience fuel injector or CP4 pump failures, which can be costly to repair. The Allison 10-speed transmission can exhibit torque converter shudder or harsh shifting. Electrical issues, especially with the infotainment system and sensors, are also reported. Exterior and Interior issues are relatively minor compared to the engine and transmission concerns. Overall, prospective buyers should thoroughly inspect the truck and consider getting a pre-purchase inspection, especially if it has the Duramax engine, to identify any potential problems. The severity of the issues ranges from minor inconveniences to major repairs, with costs ranging from a few hundred dollars for sensor replacements to several thousand for engine or transmission overhauls.