05 Most Common Allison 6 Speed Transmission Problems [+Solution]

Allison 6-speed transmissions have gained a reputation in the automotive industry for their durability and reliability. Like any mechanical component, they are not immune to problems and malfunctions. In this article, we will explore some common Allison 6 speed transmission problems that vehicle owners may encounter, providing insights into the causes of these issues and potential solutions.

In 2006, the Allison 6-speed transmission was considered one of the most powerful and reliable vehicle transmissions. Now the company offers 8-speed and 10-speed transmissions that build upon the success of the original 6-speed design. These new models feature enhanced efficiency, improved gear ratios, and advanced electronic controls to optimize performance.

Which GM Vehicles Use 6-Speed Transmission Systems?

The following vehicles are equipped with Allison 6-speed automatic transmissions:

GMC Sierra Denali2007-2013
GMC Sierra 2500HD/3500HD 6.02007-2014
GMC Sierra 15002009-2013
Chevrolet Silverado 15002010-2013
Chevrolet Silverado 2500HD/3500 HD2007-2014
Chevrolet Corvette2006-2013
Cadillac STS-V2006-2009
Cadillac XLR-V2006-2009
Cadillac Escalade EXT2007-2013
GMC Savana 2500-35002010-present
Chevrolet Suburban 15002009-2020
Chevrolet Express 2500-35002010-present
GMC Savana 2500 and 350020101-present
Chevrolet Tahoe2009-2020
GMC Yukon XL2009-2020
Chevrolet Silverado 2500HD/3500 HD2020-present
Chevrolet Silverado/GMC Sierra 15002014-2019
GMC Sierra 2500HD/3500HD2020-present

Allison 6 Speed Transmission Problems with Solution:

Allison 6 Speed Transmission Problems with Solution:

There are 5 major Allison transmission problems. Let discuss

Faulty Shift Selector:

Allison 6 Speed Transmission Problems with Solution:

The faulty shift selector poses a serious concern as it hampers the smooth transitioning between gears, especially when increasing the vehicle’s speed. When drivers attempt to change gears, they may experience delays or complete failure in engaging the desired gear.

This issue not only compromises the driving experience but also raises safety concerns since unexpected gear malfunctions can lead to accidents on the road.


Owners of Allison vehicles are urged to have their transmissions inspected by professionals if they notice any unusual delays or difficulties while shifting gears.

Limp Mode:

Allison 6 Speed Transmission Problems with Solution:

This mode is a protective measure if the system detects any abnormalities or damage within the transmission. By activating this mode, the vehicle is locked into third gear, and its speed is significantly reduced to prevent further damage. Ensuring the transmission system functions correctly when a car goes into limp mode is crucial.

The purpose behind activating limp mode is to limit any potential harm caused by continuing to operate with a damaged or malfunctioning transmission. By restricting the vehicle’s speed and locking it into third gear, Allison aims to prevent additional strain on the already compromised components and minimize any further damage that could occur.


It is a protective mechanism that activates when heavy loads surpass the capacity limit of the vehicle. This can happen when towing a trailer or carrying excessive weight in the trunk. When the limp mode is activated, the engine power is reduced significantly, limiting the vehicle’s speed and acceleration.

Another common trigger for limp mode activation is running out of coolant. The cooling system maintains an optimal engine temperature and prevents overheating. When coolant levels drop too low, the engine may experience overheating, leading to potential damage or malfunctions.

Note: Chevy Silverado is famous for its performance and durability. But there are also problems with transmission. To know the problems and their solutions, read this article. Chevy Silverado Transmission Problems with Solutions

Mis Adjustment:

Mis Adjustment:

When you replace the transmission system and start experiencing unexpected transmission problems, it could indicate a misadjustment issue. Misadjustment occurs when the newly installed transmission is not properly calibrated to your vehicle’s specifications, leading to various issues affecting its performance.


Check the installation properly or consult a qualified mechanic for proper installation.

Fluid Leakage:

Fluid Leakage:

Fluid leakage can be a serious issue regarding Allison’s 6-speed transmission. This problem often leads to low fluid levels, which can harm the overall performance and lifespan of the transmission.


  • To address this issue, it is crucial to regularly inspect the gaskets and seals for any signs of wear or damage. If identified, they should be replaced promptly by a professional mechanic using high-quality replacement parts.
  • Maintaining proper fluid levels during transmission is another important step in preventing fluid leakage.

 Faulty Parts:

Regarding the Allison 6-speed transmission, problems with faulty parts can be a persistent issue. These transmissions are renowned for their durability and efficiency, but even the best-designed systems can encounter flaws within their components. From worn-out clutches to malfunctioning solenoids, these faulty parts can cause a wide range of issues that affect performance and reliability.


To solve the problem, first, you need to check the following parts:

  • Torque converter
  • Oil pumps
  • Valve body
  • Electric wiring
  • Bushings
  • P2 Planetary
  • C2 hub
  • C2 clutches

Note: Like Chevy Silverado, GMC and Allison Duramax also faces transmission problems. But every problem has its solutions. To read the  Duramax Transmission solutions, their rebuild cost, benefits and disadvantages. Click Here 

Are 6 Speed Transmissions Good?

6 Speed Transmissions Good

When we see 6-speed Allison transmission reviews, it has many benefits.

Greatly Improves Fuel Economy:

This innovative technology is designed to greatly improve fuel economy, ensuring you get the most out of every drop of fuel. With its advanced features and intelligent design, this transmission offers several key benefits that make it an excellent choice for any vehicle owner looking to save on gas.

More Power Than Previous Generations:

Regarding power and performance, the Allison 6 Speed Transmission is setting new standards that surpass those of previous generations. With a host of benefits that enhance efficiency and functionality, this transmission has revolutionized the driving experience.

Reduced Engine Wear:

One of the most significant advantages of the Allison 6 Speed Transmission is the ability to minimize engine wear by providing precise gear shifts. By seamlessly transitioning between gears, this transmission ensures optimal engine RPMs at all times, preventing unnecessary strain on crucial components. With reduced friction and improved lubrication capabilities, you can also expect less heat generation within your engine.

Relaxed Driving:

One significant advantage of the Allison 6-Speed Transmission is its seamless shifting capabilities. With six gears at your disposal, this transmission ensures smooth transitions between gears, eliminating any jerks or jolts that can disrupt your driving rhythm.

Which is Better, 5 Speed or 6 Speed Automatic Transmission?

Which is Better, 5 Speed or 6 Speed Automatic Transmission?

While there are numerous similarities between 5-speed and 6-speed transmissions, the few fundamental differences make the 6-speed transmission superior. One significant advantage of the 6-speed transmission is its ability to allow the vehicle to operate at higher speeds while maintaining lower RPMs. This enhances the vehicle’s overall performance and contributes to reduced fuel costs.

How Do I Reset My Allison 6-Speed Transmission?

This step is crucial as it allows you to access the necessary controls without interference.  Now, in a swift motion lasting less than 3 seconds, move the shift selector from Neutral (N) to Drive (D), then back to Neutral (N), followed by Drive (D) again. Repeat this process once more by shifting from Neutral (N) to Reverse (R) and finally back to Neutral (N). N-D-N-D-N-R-N. This rapid sequence of movements prompts the system to reset itself effectively.

Final Words:

After Allison 6 Speed Transmission Problems and their solution, potential buyers and current owners must be aware of these potential issues and take appropriate measures to prevent or address them. Regular maintenance, proper fluid levels, and prompt repairs can help mitigate any potential problems.

If you are experiencing any issues with your Allison 6-speed transmission, it is recommended to consult with a certified mechanic or contact Allison Transmission directly for assistance. Taking proactive steps can ensure the smooth functioning of your vehicle’s transmission in the long run.


What are the common GM 6-speed transmission problems?

There are many problems and solutions to GM transmission.
One common issue owners report is a harsh shifting or jerking sensation when accelerating or decelerating. This can be caused by various factors, such as worn-out clutch plates, faulty solenoids, or even dirty transmission fluid.

Another frequently encountered problem is the transmission slipping out of gear while driving. This can be extremely dangerous and may necessitate immediate attention from a certified mechanic to prevent accidents on the road.

How much HP can a 6-speed Allison handle?

Depending on the specific model and configuration, a 6-speed Allison transmission can handle anywhere from 400 to 550 horsepower.

What are the solutions to Allison 2500 transmission problems?

One prevalent issue with the Allison 2500 transmission is slipping gears. This occurs when the transmission unexpectedly shifts into neutral or fails to engage properly.

To address this problem, a thorough inspection of the fluid level and quality is recommended. Low or dirty fluid levels can lead to inadequate lubrication, resulting in gear slippage. If necessary, replace the fluid filter and complete the system flush using manufacturer-recommended fluids for optimal results.

What are 6-Speed Allison Transmission Shift Selector Problems?

One of the key issues is rough shifting, where the transition between gears becomes noticeably jerky and uncomfortable for both the driver and passengers.

There are instances where the transmission refuses to shift into drive or reverse, leaving drivers stranded or unable to move their vehicles.

Another concern is the delayed response when shifting gears, resulting in a frustrating lag between pressing the gear selector and experiencing a gear change.

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