What is the 2011-2022 GMC Sierra 3500HD Turbocharger VGT Vane Sticking and Boost Control Failure (Duramax LML/L5P)?

The variable geometry turbocharger (Garrett GT3788VA on LML, and similar VGT on L5P) used on 6.6L Duramax engines develops carbon buildup on the variable vanes, causing them to stick and resulting in loss of boost control. Owners report surging, lack of power under load, black sm… Repairs typically run $200-$3,500. Severity: high.

What is the 2015-2023 GMC Sierra 3500HD Trailer brake controller / integrated trailer brake module malfunction?

Sierra 3500HD owners towing heavy loads report intermittent trailer brake output loss, warning messages, or erratic gain behavior from the integrated trailer brake controller. NHTSA complaints and GM service bulletins/diagnostics commonly point to module/software issues, poor con… Repairs typically run $80-$900. Severity: high.

What is the 2020-2024 GMC Sierra 3500HD Electric power steering (EPS) assist loss / reduced assist warnings (new body style)?

On 2020+ Sierra 3500HD (T1 platform) with electric power steering, owners report intermittent loss of steering assist and warning messages such as "Steering Assist Reduced". NHTSA complaints and GM service information commonly point to EPS module/software issues, wiring/connector… Severity: high.

What is the 2015-2024 GMC Sierra 3500HD Diesel Injector Failure Causing White Smoke and Rough Running?

The Bosch piezoelectric fuel injectors on the Duramax L5P and LML engines can fail due to contaminated fuel, high-mileage wear, or internal electrical faults. A failed injector causes white smoke on startup, rough idle, misfires on the affected cylinder, and fuel dilution of the… Repairs typically run $600-$5,000. Severity: high.

What is the 2015-2024 GMC Sierra 3500HD Rear Leaf Spring Breakage Under Heavy Loads?

The rear leaf spring packs on the Sierra 3500HD are prone to breaking or cracking under sustained heavy loads, particularly when used for frequent towing, hauling, or with fifth-wheel hitches. The main leaf or secondary leaves fracture at the spring eye or center bolt area. Broke… Repairs typically run $400-$1,500. Severity: high.

What is the 2007-2020 GMC Sierra 3500HD Allison 1000/2000 Series Transmission Torque Converter Shudder?

The Allison 1000 and 2000 series automatic transmissions paired with Duramax engines in the Sierra 3500HD exhibit torque converter clutch shudder during light throttle cruising between 40–65 MPH as the TCC applies and releases. This is caused by degraded transmission fluid, worn… Repairs typically run $150-$2,200. Severity: medium.

What is the 2007-2022 GMC Sierra 3500HD Front Differential Actuator Failure Causing 4WD Engagement Problems?

The front axle disconnect actuator (also called the front axle engagement actuator or IWE—Integrated Wheel End) on four-wheel-drive Sierra 3500HD models is known to fail, preventing proper engagement or disengagement of 4WD. Owners report grinding noises from the front axle area… Repairs typically run $150-$800. Severity: medium.

What is the 2011-2020 GMC Sierra 3500HD Diesel Exhaust Fluid (DEF) System Failures?

The Duramax diesel Sierra 3500HD (2011+) equipped with the DEF/SCR emission system develops failures in the DEF tank heater, DEF quality sensor, and associated wiring. Wires to the DEF tank short out, and because they share a harness with the transmission, this can trigger both D… Repairs typically run $300-$2,000. Severity: medium.

What is the 2015-2024 GMC Sierra 3500HD Exhaust Manifold Cracking and Warping (Duramax L5P/LML)?

The cast iron exhaust manifolds on the Duramax diesel engine are prone to cracking and warping due to extreme exhaust gas temperatures and thermal cycling. Cracks typically develop at the manifold-to-head mounting points, causing exhaust leaks that produce a ticking noise on cold… Repairs typically run $800-$2,500. Severity: medium.

What is the 2015-2024 GMC Sierra 3500HD Steering Gear Box Leak and Excessive Play?

The recirculating ball steering gear box on the Sierra 3500HD develops fluid leaks at the input shaft seal and sector shaft seal, leading to power steering fluid loss and increased steering play. The heavy-duty application and large tires accelerate wear on the steering box inter… Repairs typically run $400-$1,500. Severity: medium.

What is the 2015-2020 GMC Sierra 3500HD Dashboard Instrument Cluster Pixel and Display Failure?

The instrument cluster in 2015-2020 Sierra 3500HD trucks suffers from LCD pixel failure, causing portions of the Driver Information Center (DIC) display to become unreadable. Individual pixels or entire segments go blank, making it impossible to read trip computer data, gear indi… Repairs typically run $150-$1,000. Severity: low.

GMC · Known Issues

2020 GMC Sierra 3500HD Problems: 13 Known Issues

2020 model year · 1,865+ owner reports · Updated September 2026

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According to Au7o's analysis of 1,865+ owner reports, the 2020 GMC Sierra 3500HD has 13 documented known issues, with 7 rated critical. The most serious are CP4.2 High-Pressure Fuel Pump Catastrophic Failure ($10,000-$18,000 repair), DPF (Diesel Particulate Filter) Clogging and Regeneration Failure ($300-$3,500 repair), Turbocharger VGT Vane Sticking and Boost Control Failure (Duramax LML/L5P) ($200-$3,500 repair), Trailer brake controller / integrated trailer brake module malfunction ($80-$900 repair), Electric power steering (EPS) assist loss / reduced assist warnings (new body style), Diesel Injector Failure Causing White Smoke and Rough Running ($600-$5,000 repair) and Rear Leaf Spring Breakage Under Heavy Loads ($400-$1,500 repair). The most commonly reported issue is CP4.2 High-Pressure Fuel Pump Catastrophic Failure with 440 owner reports.

Frequently Asked Questions

What are the most common GMC Sierra 3500HD problems?

According to Au7o's analysis of 1,865+ owner reports, the 2020 GMC Sierra 3500HD has 13 documented issues. The most frequently reported are: CP4.2 High-Pressure Fuel Pump Catastrophic Failure, DPF (Diesel Particulate Filter) Clogging and Regeneration Failure, Turbocharger VGT Vane Sticking and Boost Control Failure (Duramax LML/L5P). Of these, 7 are rated critical and should be addressed promptly.

Is the GMC Sierra 3500HD reliable?

The 2020 GMC Sierra 3500HD has 13 known issues documented across 1,865+ owner reports. 7 issues are rated critical: CP4.2 High-Pressure Fuel Pump Catastrophic Failure and DPF (Diesel Particulate Filter) Clogging and Regeneration Failure and Turbocharger VGT Vane Sticking and Boost Control Failure (Duramax LML/L5P) and Trailer brake controller / integrated trailer brake module malfunction and Electric power steering (EPS) assist loss / reduced assist warnings (new body style) and Diesel Injector Failure Causing White Smoke and Rough Running and Rear Leaf Spring Breakage Under Heavy Loads. Prospective buyers should inspect for these issues and factor potential repair costs into their purchase decision. Regular maintenance following the manufacturer's schedule helps prevent many common problems.

How much does it cost to fix common GMC Sierra 3500HD problems?

Repair costs for known GMC Sierra 3500HD issues range from $80 to $18,000, depending on the specific problem and whether you choose DIY or professional repair. The most critical issue, CP4.2 High-Pressure Fuel Pump Catastrophic Failure, typically costs $10,000-$18,000 to repair. Au7o provides step-by-step DIY maintenance guides that can help reduce repair costs.

What is the 2011-2020 GMC Sierra 3500HD CP4.2 High-Pressure Fuel Pump Catastrophic Failure?

The Sierra 3500HD Duramax diesel uses the same Bosch CP4.2 high-pressure fuel pump as the 2500HD. The pump is prone to catastrophic failure that destroys the entire fuel injection system (all 6 injectors, fuel rails, return lines). The 3500HD is often used for heavier towing and… Repairs typically run $10,000-$18,000. Severity: high.

All 13 Known Issues

Other GMC Models

Frequently Asked Questions

What are the most common GMC Sierra 3500HD problems?

Is the GMC Sierra 3500HD reliable?

How much does it cost to fix common GMC Sierra 3500HD problems?

What is the 2011-2020 GMC Sierra 3500HD CP4.2 High-Pressure Fuel Pump Catastrophic Failure?

What is the 2011-2022 GMC Sierra 3500HD DPF (Diesel Particulate Filter) Clogging and Regeneration Failure?

When Issues Typically Appear

2011-2020 GMC Sierra 3500HD: CP4.2 High-Pressure Fuel Pump Catastrophic Failure#

2011-2022 GMC Sierra 3500HD: Turbocharger VGT Vane Sticking and Boost Control Failure (Duramax LML/L5P)#

2011-2020 GMC Sierra 3500HD: Diesel Exhaust Fluid (DEF) System Failures#

2015-2023 GMC Sierra 3500HD: Trailer brake controller / integrated trailer brake module malfunction#

2020-2024 GMC Sierra 3500HD: Electric power steering (EPS) assist loss / reduced assist warnings (new body style)#

2011-2022 GMC Sierra 3500HD: DPF (Diesel Particulate Filter) Clogging and Regeneration Failure#

2015-2024 GMC Sierra 3500HD: Diesel Injector Failure Causing White Smoke and Rough Running#

2015-2024 GMC Sierra 3500HD: Rear Leaf Spring Breakage Under Heavy Loads#

2007-2020 GMC Sierra 3500HD: Allison 1000/2000 Series Transmission Torque Converter Shudder#

2007-2022 GMC Sierra 3500HD: Front Differential Actuator Failure Causing 4WD Engagement Problems#

2015-2024 GMC Sierra 3500HD: Exhaust Manifold Cracking and Warping (Duramax L5P/LML)#

2015-2024 GMC Sierra 3500HD: Steering Gear Box Leak and Excessive Play#

2015-2020 GMC Sierra 3500HD: Dashboard Instrument Cluster Pixel and Display Failure#