2018 GMC Sierra 3500 HD

The 2018 GMC Sierra 3500 HD is a heavy-duty pickup truck known for its towing and hauling capabilities. Engine options include the 6.0L Vortec V8 (360 hp, 380 lb-ft torque) and the 6.6L Duramax turbodiesel V8 (445 hp, 910 lb-ft torque). The 6.0L is paired with a 6-speed automatic transmission, while the 6.6L Duramax is paired with an Allison 1000 6-speed automatic transmission. Owners often praise the truck’s powerful engines, comfortable ride (for a heavy-duty truck), and spacious cabin. Common complaints include the truck’s large size making it difficult to maneuver in tight spaces and some reliability concerns.

Engine

6.6L Duramax Diesel V8 (L5P)

• Fuel Injector Failure
  • Description/Symptoms: Rough running engine, misfires, excessive smoke, decreased fuel economy. Can occur on one or more injectors.
  • Solution: Replacement of faulty fuel injector(s). Requires specialized tools and knowledge.
  • Estimated Cost to Fix: $800 - $1200+ per injector (depending on labor and parts).
  • Recalls: None Found
• CP4 Fuel Pump Failure
  • Description/Symptoms: Engine stalls, won’t start, metallic debris in the fuel system, potential damage to the entire fuel system. The CP4 pump is known to fail catastrophically when contaminated with even small amounts of water or debris.
  • Solution: Replacement of the CP4 pump and potentially cleaning or replacing the entire fuel system (fuel lines, injectors, fuel rails, etc.)
  • Estimated Cost to Fix: $8,000 - $12,000+
  • Recalls: None Found
• Diesel Exhaust Fluid (DEF) System Issues
  • Description/Symptoms: “Service Exhaust Fluid System” message, reduced engine power, potential engine shutdown. Common causes include faulty DEF sensors, DEF pump failure, DEF heater failure, and DEF quality issues.
  • Solution: Diagnosis to determine the specific component failure, followed by replacement of the faulty component (sensor, pump, heater, etc.) or draining and refilling with fresh, high-quality DEF.
  • Estimated Cost to Fix: $300 - $2000+ (depending on the component)
  • Recalls: None Found

6.0L Vortec V8 (L96)

• Oil Consumption
  • Description/Symptoms: Excessive oil consumption, requiring frequent oil top-offs between oil changes. May be accompanied by blue smoke from the exhaust.
  • Solution: Diagnosis to determine the source of the oil consumption (worn valve seals, piston rings, etc.). Potential repairs include valve seal replacement, piston ring replacement, or engine replacement.
  • Estimated Cost to Fix: $500 - $5000+ (depending on the severity and repair required)
  • Recalls: None Found

Transmission

Allison 1000 6-Speed Automatic (Diesel)

• Torque Converter Shudder/Vibration
  • Description/Symptoms: Shudder or vibration felt during light throttle acceleration, typically in the 35-50 mph range.
  • Solution: Fluid flush, replacement of the torque converter.
  • Estimated Cost to Fix: $600 - $2500+
  • Recalls: None Found
• Shift Flare/Harsh Shifts
  • Description/Symptoms: Transmission slips or hesitates during shifts, or shifts harshly. Can be caused by low fluid, worn clutches, or valve body issues.
  • Solution: Fluid flush and filter change, valve body replacement, or transmission rebuild/replacement.
  • Estimated Cost to Fix: $200 - $5000+ (depending on the severity and repair required)
  • Recalls: None Found

6L90 6-Speed Automatic (Gas)

• Harsh Shifts
  • Description/Symptoms: Harsh or jerky shifts, particularly when cold. Could be caused by worn valve body components or issues with the TCM (Transmission Control Module).
  • Solution: Transmission fluid flush and filter change, valve body replacement, or TCM reprogramming/replacement.
  • Estimated Cost to Fix: $200 - $2000+ (depending on the severity and repair required)
  • Recalls: None Found

Suspension

• Leaf Spring Squeaking
  • Description/Symptoms: Annoying squeaking noise coming from the rear suspension, especially when going over bumps or turning.
  • Solution: Lubricating the leaf spring bushings and contact points. If the bushings are worn, replacement is necessary.
  • Estimated Cost to Fix: $50 - $500+ (depending on lubrication vs. bushing replacement)
  • Recalls: None Found

Electrical

• Battery Drain
  • Description/Symptoms: Battery drains overnight or over a few days, resulting in a no-start condition.
  • Solution: Diagnose and repair the source of the parasitic drain (e.g., faulty module, aftermarket accessory).
  • Estimated Cost to Fix: $100 - $500+ (depending on the complexity of the drain)
  • Recalls: None Found
• Infotainment System Freezing/Crashing
  • Description/Symptoms: Infotainment screen freezes, crashes, or becomes unresponsive.
  • Solution: Software update, replacement of the infotainment module.
  • Estimated Cost to Fix: $100 - $1200+
  • Recalls: None Found

Exterior

• No Issues Found

Interior

• Cracked Dashboard
  • Description/Symptoms: Cracks appearing on the dashboard, especially in warmer climates.
  • Solution: Replacement of the dashboard.
  • Estimated Cost to Fix: $800 - $2000+
  • Recalls: None Found

Summary

The 2018 GMC Sierra 3500 HD can suffer from a range of issues, with the most serious potentially stemming from the Duramax diesel engine’s fuel system. CP4 pump failures can be catastrophic and extremely costly. Other common issues include DEF system problems and potential issues with the Allison transmission. The 6.0L gas engine can also have oil consumption issues, while the infotainment system and electrical system can have gremlins that can be difficult to track down. Repair costs range from a few hundred dollars for simple fixes to over $10,000 for major engine or transmission repairs. While most issues aren’t inherently dangerous, a CP4 failure could cause a sudden engine stall, which could be dangerous if you’re towing a heavy load.