The Most Common 2021 GMC Sierra Transmission Problems: A Comprehensive Guide

Nov 14, 2023

If you are in the market for a capable full-sized pickup truck but don’t want to pay new vehicle prices, the 2021 GMC Sierra 1500 seems like a great choice. This vehicle has a bold front grill, built-in steps on either side of the bed, various trim and equipment options, and a few powerhouse engine options.

However, once you look past the truck’s bold, appealing exterior, you will find that it is known for a handful of manufacturing defects and mechanical issues. Whether you have already made your purchase or are considering investing in the 2021 GMC Sierra 1500, you need to familiarize yourself with these issues to protect your rights as a consumer.

Hundreds of vehicle owners have reported 2021 GMC Sierra transmission problems. In fact, GM had to start replacing eight-speed transmissions in 2021 models of Sierras and Chevrolet Silverados just a few months after their hallmark trucks hit the market.

In this 2021 GMC Sierra transmission problems breakdown, we will highlight the malfunctions you must know, including performance issues, rough shifting, and total transmission failures. We also discuss this full-sized truck’s overall reliability and other 2021 GMC Sierra 1500 problems, such as power equipment failures, engine issues, and more.


Is the 2021 GMC Sierra Reliable?

According to Consumer Reports, the 2021 GMC Sierra was one of the least reliable pickup trucks when released. Since then, various mechanical issues have further eroded this truck’s reputation.

Surprisingly, 2021 GMC Sierra transmission problems were not at the top of Consumer Reports’ list of concerns. At the time of the initial report, the manufacturer had addressed many of the GMC Sierra transmission problems that had plagued previous models. However, in the years following the launch of the 2021 Sierra, many of the same old issues emerged, including:

  • Shuddering
  • Harsh shifting
  • Loss of power
  • Hesitation

The 2021 GMC Sierra 1500 has also demonstrated issues with its brakes, in-car electronics, power equipment (i.e., windows, locks, etc.), and engine.

To make matters worse, the 2021 version of the GMC Sierra has been the subject of at least four different recalls. GM issued two recalls for the vehicle’s seat belts and one for its ABS system. They also had to recall hundreds of Sierras to address the aforementioned eight-speed transmission malfunctions. In addition, several full-sized pickups outpaced the 2021 Sierra regarding reliability that year, including the Ford F-150 and the Ram 1500.

Despite all this, the Sierra still sold very well, and thousands are on the road across the country. Admittedly, the vehicle offers a luxurious riding experience, is available in several packages, and looks great.

That said, with so many documented issues, you need to keep a close eye on your GMC Sierra, especially while it is under the original factory warranty. As long as you have a valid factory warranty, you will be protected from any significant issues that might arise.


2021 GMC Sierra Problems

Any mass-produced vehicle will inevitably experience some problems. After all, manufacturing processes are far from perfect. But some makes and models, including the 2021 GMC Sierra 1500, are prone to far more issues than your average car or truck.

Some 2021 GMC Sierras experience so many problems that they can be classified as “lemons.” This term refers to any vehicle that experiences a significant malfunction or defect that makes it unsafe to drive. Suppose a dealer cannot sufficiently repair a faulty vehicle after a set number of attempts (usually three or four in most states). In that case, they may have to replace the vehicle or refund the owner under the Lemon Law.

Defects to non-critical equipment, such as turn signals or side mirrors, do not make a vehicle a lemon. However, transmission, brake, engine, and power equipment failures can create serious safety issues for drivers. Unfortunately, the 2021 GMC Sierra is known for all sorts of problems that can make them unsafe to drive, including the following:

Faulty Brakes

The GMC Sierra 1500 is a relatively heavy full-sized pickup truck. Considering how large the truck is, the last issue you want to encounter is faulty brakes. However, this is one of the significant problems the truck is known for.

Some critical components of a vehicle’s braking system are the calipers, master cylinders, and rotors. If any of these parts is compromised, you can experience reduced braking power or a total brake failure.

On their own, faulty brakes are a big concern. This 2021 GMC Sierra issue is magnified by the fact that brake issues can emerge without warning. Even if you pay close attention to your vehicle and its performance, sudden malfunctions could leave you with a significant braking power decrease. That increases the likelihood of a traffic accident, which could cause severe injuries for all involved.

If your GMC Sierra is experiencing brake issues, immediately take it to the dealer. If you believe the vehicle is unsafe, consider having it towed to the dealer. When a repair is being made under warranty, the dealer/manufacturer will usually cover the cost of the tow as well.

Pay close attention to your stopping power to mitigate the risks of braking problems with your 2021 GMC Sierra. If you ever notice a sudden decrease in braking power or hear an unusual noise when pressing the brake pedal, you may have a problem on your hands.

Engine Issues

For the 2021 Sierra model year, GMC offered the following five engines options:

  • 2.7L turbocharged engine with 310 horsepower
  • Duramax 3.0L turbo-diesel engine with 277 horsepower
  • 4.3L V6 engine with 265 horsepower
  • 5.3L Ecotec3 V8 engine with 355 horsepower
  • 6.2L EcoTec3 V7 engine with 420 horsepower

2021 GMC Sierra engine problems are not as common as transmission issues. However, the two most powerful 2021 Sierra engines are known for a few major issues.

2021 GMC 5.3 engine problems include:

  • Engine stalling
  • A lack of power or acceleration
  • Shuddering

2021 GMC 6.2 engine problems include:

  • Engine stalling
  • Inability to accelerate past a certain threshold
  • Shuddering

Engine stalling is particularly dangerous, as it can prevent you from accelerating or cause your vehicle to come to a dead stop. Engine stalling is especially concerning if it occurs when you’re attempting to merge into traffic or clear an intersection. In some cases, drivers did not experience a full-fledged stall, but their vehicles would not accelerate past 60 miles per hour.

Typically, your vehicle’s check engine light should inform you of an issue with your powertrain. However, with the 2021 GMC Sierra, your engine light may not come on until your vehicle has already begun shuddering or stalling.

If you experience stalling issues, take your truck to the dealership immediately. Also, promptly address any warning lights, including the check engine light. The sooner you have your vehicle inspected by a licensed professional, the better your chances of preventing any severe damage. And as always, have your truck towed if you believe driving is unsafe.

Power Equipment Failures

The 2021 GMC Sierra is known for its user-friendly and sophisticated infotainment system. Its higher trim levels have an exceptionally robust interior and set of electrical equipment, including a touchscreen interface, heated and cooled seats, power mirrors, windows, locks, and much more.

With so much power equipment packed into this full-sized pickup truck, it is no surprise that the 2021 GMC Sierra is known for several malfunctions. One of the most dangerous is an electrical fire. In rare instances, a short in the wiring system can cause overheating and potentially a fire.

Do you remember those convenient power seats we mentioned? They can also malfunction, leaving you unable to adjust your seating position. Under the best circumstances, being unable to modify your seats can be mildly inconvenient. But if your seat is stuck in an extreme position, you may experience reduced visibility and limited access to your pedals, steering wheel, and shifter.

Another piece of power equipment that can fail is the power steering system. A vehicle’s power steering system reduces the force you need to exert to turn your steering wheel. This feature makes it easier to control your vehicle at low speeds.

If the power steering system fails suddenly, maneuvering your vehicle will be more challenging. Navigating curves and tight turns will be especially difficult with no power steering. Other power equipment that can fail in your 2021 GMC Sierra includes electric mirrors, locks, windows, the power sunroof, and your tailgate release system.

Transmission Problems

The GMC Sierra 1500 transmission offers two options: an eight-speed or a ten-speed automatic. An eight-speed transmission has eight different gears, whereas a ten-speed transmission has 10. The eight-speed option was the standard transmission for the 2021 model year, but specific Sierra 1500s were eligible for the ten-speed.

GMC Sierra transmissions are known for exhibiting a wide range of issues, which makes them one of the most unreliable components of the 2021 GMC Sierra pickup truck. The eight-speed transmission is undoubtedly the more troubled of the two options available for the 2021 model year.

In early 2021, GM had to replace several hundred eight-speed automatic transmissions in Chevy Silverado 1500 and GMC Sierra 1500 pickup trucks. The affected vehicles had a broken reaction carrier ring, part of the transmission’s rotating assembly and critical to its operation.

While GM reported that this would not directly impact safety, it could cause a total transmission failure. That potential result is likely why they opted to replace rather than repair the transmissions.

GM’s choice to preemptively replace these faulty transmissions demonstrated the company’s commitment to resolving Sierra’s ongoing transmission issues. Despite the 1500 Sierra’s many imperfections, 2021’s transmission problems have proven far less common than in previous years.

That said, even if your truck was not affected by the broken reaction carrier ring defect, you should be aware of potential problems. Some major issues that might occur include rough shifting, shuddering, and hesitation.

The first sign, rough shifting, happens when your vehicle has difficulty transitioning from one gear to another. You may hear a clunk or other unpleasant noise or feel a distinctive jump as your truck shifts into the next gear.

Then comes the second indication, a shuddering malfunction, as a vibration shakes the entire truck. It can occur at any gear but usually happens during rapid acceleration. And the third sign is hesitation, less severe as shuddering or rough shifting. However, it is characterized by a distinct delay during acceleration.

If you notice any of these 2021 GMC Sierra transmission problems, take action immediately — especially if you are approaching the end of your truck’s factory warranty.


Settle Your Lemon Law Claim With Timothy Abeel & Associates

Your truck may be a lemon if you have encountered repeated 2021 GMC Sierra 1500 transmission problems or other equipment malfunctions. The exact definition of a lemon varies by state.

However, a vehicle is generally considered a lemon if it has a significant defect or malfunction that makes it unsafe to drive. A faulty transmission, defective brakes, or a non-working engine are a few malfunctions that lemon vehicles often experience.

Your vehicle must have an unreasonable repair history or have been rendered unusable for an extended period due to repair-related delays to qualify for a claim under your state’s Lemon Laws.

While the exact number of repairs or out-of-service time varies by state, most jurisdictions require at least three repair attempts for the same issues or six repairs total. Under the out-of-service clause, your vehicle must have been unusable for approximately 30 days to be eligible.

To determine whether your GMC Sierra transmission problems or other mechanical defects make you eligible for a Lemon Law claim, connect with the experts at Timothy Abeel & Associates. Our streamlined Lemon Law process makes it easy to determine whether you have a case so that you can exercise your consumer rights.

Our experienced team of attorneys will evaluate your case, help you explore your options, and fight for justice on your behalf. To get started, connect with our team today.

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