05 Allison 6 Speed Transmission Problems with Solution

Many vehicles use Allison’s 6-speed transmission system, which is known for its reliability and performance.

It was one of the most powerful transmissions you were proud to have in your vehicle in 2006.

Currently, Allison produces 8 and 10-speed transmissions, which are upgrades of the 6-speed transmission, but the Allison 6-speed transmission is still worth having in your car.

In this article, I have discussed some major Allison 6 speed transmission problems and their solutions.

The Allison 6-speed transmissions have 05 common problems, including faulty gear selectors, transmission limp modes, wrong adjustments, fluid leakages, and faulty parts.

Let us discuss them thoroughly with easy solutions.

1. Allison 6 Speed Transmission Problems: Faulty Shift Selector

allison 1000 6 speed transmission problems

Allison’s 6-speed transmission has problems with shift selectors and delays responses.

It is possible that the gear won’t work correctly when you increase the vehicle’s speed and change gears.

This is because of a faulty gear or shift selector.


Your transmission needs to be diagnosed quickly; otherwise, it could damage other parts.

For proper treatment, take the vehicle to a dealership or a repair shop.

2. Limp Mode

duramax allison transmission 6-speed problems

It is common for the 6-speed transmission to go into limp mode.

The limp mode is triggered when the system detects anything wrong with the transmission or if the transmission is damaged.

Allison uses this feature as a protective measure.

Activating this mode locks the vehicle into third gear and reduces engine power and vehicle speed.

When the car goes into limp mode, make sure the transmission system is working correctly.


The limp mode is activated when heavy loads exceed the vehicle’s capacity limit.

Another reason is coolant running out.

To avoid limp mode, avoid excessive loading and add coolant if necessary.

Use high-quality coolants for better performance.

Should the problem persist after applying the procedure, take the vehicle to the dealer.

Learn: How to Get Allison Transmission Out of Limp Mode

3. Mis Adjustment

6 speed allison transmission problems

Your vehicle may need transmission adjustment if you replace the transmission system and experience transmission problems.

This problem is caused by improper installation of the transmission.


Check the installation properly.

Consult a qualified mechanic if you are having trouble checking the adjustment.

4. Fluid Leakage

Transmission Fluid Leakage

Allison’s 6-speed transmission has a leakage problem, which leads to low fluid levels.

Take it seriously and conduct the necessary measurements.


For an immediate solution, seal the leaks.

A mechanic can then provide you with a proper diagnosis.

The solution to this problem can be seen in the video below:

5. Faulty Parts

If your transmission adjustment is imperfect, one or more parts may be faulty.

Your transmission may have a faulty part if it does not work properly.


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

  1. Torque converter
  2. The oil pumps
  3. The valve body
  4. The electronic wiring
  5. The Bushings
  6. The P2 Planetary
  7. The C2 hub
  8. The C2 clutches
  9. And input shaft

The part mentioned will cause Allison 6-speed transmission problems.

Check these parts if your transmission isn’t working.

Signs of Allison Transmission Going Out

Allison transmissions require proper maintenance and care.

If the transmission is not maintained properly, the chances of wear and tear increase and result in a costly repair.

However, it is not always possible to identify whether a transmission is in good condition or not.

Therefore, I have mentioned some major signs of Allison transmissions going out.

The symptoms of a bad transmission are:

  • Check engine warning light
  • Delay response
  • Transmission fluid leaks
  • Grinding or clunking noise

These signs are red flags for your Allison transmission and when you notice them take your vehicle to a repair shop as soon as possible.

What Year Did the 6 Speed Allison Come Out?

Allison’s 6-speed transmission was introduced in 2006.

In the years prior to it, GM trucks were equipped with Allison 5-speed automatic transmissions.

Which GM Vehicles Use 6 Speed Transmission System?

A large number of pickup trucks use Allison 6-speed transmissions.

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

  • GMC Sierra Denali [2007-2013]
  • GMC Sierra 2500HD/3500HD 6.0 [2007-2014]
  • GMC Sierra 1500 [2009-2013]
  • Chevrolet Silverado 1500 [2010-2013]
  • Chevrolet Silverado 2500HD/3500 HD [2007-2014]
  • Chevrolet Corvette [2006-2013]
  • Cadillac STS-V [2006-2009]
  • Cadillac XLR-V [2006-2009]
  • Cadillac Escalade EXT [2007-2013]
  • GMC Savana 2500-3500 [2010-present]
  • Chevrolet Suburban 1500 [2009-2020]
  • Chevrolet Express 2500-3500 [2010-present]
  • GMC Savana 2500 and 3500 [20101-present]
  • Chevrolet Tahoe [2009-2020]
  • GMC Yukon XL [2009-2020]
  • Chevrolet Silverado 2500HD/3500 HD [2020-present]
  • Chevrolet Silverado/GMC Sierra 1500 [2014-2019]
  • GMC Sierra 2500HD/3500HD [2020-present]

Are All Allison 1000 Transmissions 6 Speed?

No, not all Allison 1000 transmissions are 6-speed.

Allison 1000 transmissions are available in 5-speed and 6-speed versions.

Are 6 Speed Transmissions Good?

The Allison 6-speed transmission is one of the market’s most popular and reliable automatic transmission systems.

It is widely used because of its many benefits.

Allison’s 6-speed transmission offers the following benefits:

  1. Greatly improves fuel economy
  2. More power than previous generations
  3. Reduced engine wear
  4. Relaxed driving

Which is Better 5 Speed or 6 Speed Automatic Transmission?

Which is Better 5 Speed or 6 Speed Automatic Transmission

There are many similarities between 5-speed and 6-speed transmissions.

Just a few fundamental differences make the 6-speed better than the 5-speed transmission.

6-speed allows the vehicle to run at higher mph with lower RPMs and which increases fuel mileage.

Allison 4000 Transmission Problems

Allison 4000 and Allison 6-speed transmission share some common characteristics, but they are not exactly same.

As a result, their problems are not the same.

Some common problems with Allison 4000 transmissions are:

  • Shifting Issues: The Allison 4000 transmission has shifting issues. Drivers often experience hard or delayed shifting, slipping gears, and clunking noises in Allison 4000 transmissions.
  • Performance Problems: Some drivers complain about power losses in Allison 4000 transmission. Including performance issues, unusual vibrations and leaking fluid are also common in this transmission.
  • Buring Smells: Some Allison 4000 transmissions have this problem. When burning smells coming from the transmission, take it seriously. Otherwise, it can cause severe problems.

How Do I Reset My Allison 6 Speed Transmission?

The easiest way to reset the Allison 6-speed transmission is as follows:

  1. Start the vehicle without starting the engine.
  2. In a quick motion (less than 3 seconds), move the shift selector N-D-N-D-N-R-N.

The warning light will be reset.

Read also: GM 10 speed transmission problems.


What is the common Allison 6 speed automatic transmission problems?

The most common Allison 1000 6-speed transmission problems are:

  • Vehicle stuck
  • Delay gear shifting
  • Leakages

How much HP can a 6 speed Allison handle?

A 6-speed Allison transmission can handle up to 400 to 550 hp and 500 to 1050 lb.-ft of torque.

How much is a 6 speed Allison transmission?

The cost of a 6-speed Allison transmission is approximately $6830 in the USA.

How do I know if I have a 6 speed Allison?

You can find the transmission type listed in your owner’s manual.

A window sticker also displays the name and model of the transmission system.

Is the Allison 2000 a 6 speed?

Yes, the Allison 2000 is a 6-speed transmission.

Allison 2000 transmission is designed for small buses and public transportation.

How much does a 6 speed Allison transmission weigh?

The approximate weight of a 6-speed Allison transmission is 300 to 350 pounds or 136.078 to 158.757 kg.

What is the operating temperature of a Allison 6 speed transmission?

The operating temperature of an Allison 6-speed transmission is approximately 170 to 210 degrees.

When towing off-roads in summer, the temperature rises to 230 degrees.

What is 6 Speed Allison Transmission Shift Selector Problems?

The shift selector problems in the Allison 6-speed automatic transmission mean:

  • Transmission is rough shifting
  • Will not shift into drive or reverse
  • Delay response when shifting gears

Final Words

Although the Allison 6-speed transmission has a few issues, it’s reliable and performs well.

It’s okay to go for it without hesitation.

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