The Mercedes-Benz Transmission

You might be one of the fortunate people to own or drive a Mercedes Benz. Owning one of the world’s better built vehicles, however, will not exempt you from experiencing transmission problems like the rest of us.Although we see less of these vehicles in for repairs, which may only mean that there are less of them on the road, Mercedes will still experience transmission trouble from time to time and will need the experience and knowledge of a highly trained transmission repair specialist.

Mercedes uses different variations of transmissions across different years and models, but here is a list of some of the most common variations on the road today:

722.0    Three Speed

722.1    Four Speed/4 Bolt Pan

722.2    Four Speed/4Bolt Pan

722.3    Four Speed/6Bolt/Large Case

722.4    Four Speed/6Bolt/Small Case

722.5    Five Speed Overdrive

722.6    Six Speed Overdrive

722.9    Seven Speed Overdrive

Possibly the most common of these is the 722.6, so we will discuss that model for simplicity.

The 722.6 is also called a NAG1 (New Automatic Gearbox 1st Version) or a 5G-Tronic. This transmission is electronically controlled, which means it’s a shift by wire. According to Mercedes Benz, this transmission is sealed for life, which is why there is no dipstick to check your fluid level.

However, in recent years, Mercedes has published an article calling for a transmission fluid and filter change at 39,000 miles. This was added into the 2007 and later model year maintenance books. The 2006 model year book has a recommendation for maintenance checks for high mileage vehicles at 143,000 miles.

When servicing the transmission, Mercedes recommends the use of genuine Mercedes fluid; however, this can be substituted for fluid that is on their approved list of acceptable fluids.

Common Problems That Occur

As with any transmission, Mercedes transmissions also have their own common problems that, unless addressed immediately, can cause major problems. Here are some of the major issues that we run into with Mercedes transmissions:


The majority of leaks come from the 13-pin electrical connector and the shifter mechanism bellow.The 13-pin connector can leak either internally or externally. In some, the leak will even wick up the harness to the ETC (electronic control module), causing the module to short out as well. Mercedes has an updated connector now available for this condition.

Most models have a cup holder near the shifter, where, of course, we place our drinks. We sometimes get a little careless and might even spill a little on the shifter. Well, located under that shifter is a shift module, which does not function as it should when it has coffee or other liquid splashed on it. This can cause your check engine light to come on, cause you to have codes for gear ratio errors, and also put you into limp mode, meaning you are running only on the gear that was engaged at the time.

Removing and cleaning the module will sometimes, but not always, eliminate the problem. Even if you are able to do a good cleaning, the computer will have to be checked, cleared, and reset to be sure that no additional damage was done. Obviously, you don’t want to continue driving with this malfunction as serious internal damage may occur.

Limp Mode

This occurs when the transmission control module (ETC) detects an active or intermittent problem and then won’t allow gear shifting in order to avoid serious internal damage.

Limp mode has two classifications, the first being mechanical-hydraulic emergency running mode. In this mode, the transmission locks into third gear or the lastknown “good” gear.The second type of mode is electric emergency running mode. In this mode, whatever gear was engaged is retained and a fault code is stored. When you turn off the ignition and restart again, the transmission is locked into second and reverse only. When you try to shift from park to reverse, drive, or neutral, you will heara harsh engagement clunk.

This does not necessarily mean you need to replace your transmission, but it absolutely needs to be look at by a professional transmission mechanic. In a majority of cases, a simple replacement of the conductor plate is all that will be required. The conductor plate is attached to the top of the valve body and consists of two sensors and six solenoids. The two speed sensors are usually what fail, and when they do, the ETC does not know the input or output speeds and won’t know what gear to engage the transmission in. The speed sensors cannot be replaced separately, so the whole plate must be replaced.

A proper diagnosis from one our certified technicians will determine what type of problem you may be experiencing to determine if the repairs required will be a minor repair as the one described above or something more substantial. We have the experience and knowledge to solve all of your transmission needs, even on your seemingly elusive Mercedes transmission. Come by one of our four locations today!

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