Service Required Do Not Shift Gears: Causes & Fixes

Driving is usually an enjoyable experience until you encounter one of these errors message on your cluster display.  

My first encounter with the Service Required Do Not Shift Gear was with my 2015 Mercedes Benz CLA250. I was trying to get out of the garage when the message popped up while the car refused to start.

If you see this error code and need help with why or what to do, this article is for you!

This article will look at the causes of the error message and how to remedy it. Let’s get right into it!

What is “Service Required: Do Not Shift Gears”?

The service required: Do not shift gears usually signifies something has gone wrong with your transmission system, preventing your car from changing gears.

Typically, if you see the error message on your cluster display, it could mean that the Intelligent Servo Module (ISM) is faulty. 

The Intelligent Servo Module  (ISM) is responsible for gear selection in the Mercedes Benz. It is an interface between the transmission system and other components of the vehicle, such as the Engine Control Unit (ECU) or the gear selector.

The ISM responsibilities can be summarized as follows:

1. Gear selection: The ISm receives a Signal from the gear selector and transfers the signal to the transmission, which engages the gear to shift to park (P), neutral (N), reverse (R), or drive (D).
2. Transmission communication: The ISM interface communicates between the ECU and the transmission to ensure a smooth transition between gears and operations.
3. Fault detector: The ISM can detect and store codes relating to transmission issues in the car.

Furthermore, other causes of the error message will be discussed in later paragraphs, but the ISM is the most common.

Where is the ISM located?

The ISM, also known as the shift module, is mounted by the side of the transmission casing. Although, the exact location of the module will depend on the model and year of the car. You don’t usually need to lose the transmission to access the module. However, you will need to get under the vehicle.

Other causes of Service Required Do Not Shift Gears

Other than ISM malfunction, there are a few reasons your Mercedes Benz may be getting the “Do not shift gear” error. Below are some of the causes we suspect are causing the error:

1. Bad or dead Auxillary Battery

Another reason you may be getting this error could be that your secondary auxiliary battery is dead.  Usually, this will follow with your car shutting off or difficulty in starting.  To reset this, turn off the car for a few seconds and try again. It should fix the vehicle temporarily. 

To locate the Auxilliary battery, it is usually under the passenger carpet and the glove box.

Furthermore, most vehicles are designed so that the auxiliary battery supply power to other components, including the gear shifting. Therefore, a dead aux battery can disrupt the entire transmission system, including the Intelligent Servo Module (ISM).

2.  Software issue

Most modern vehicles like your Mercedes Benz are heavily software-reliant. As established before, the gearing process relies on the IS module, a software interface. Occasionally, the error message may be caused by glitches, outdated software, and more. We recommend checking the system for software updates on specific modules.

3. Sensor malfunction

Note that the ISM and other modules rely on data or signals from sensors, which it feeds to the transmission system. Incorrect data could trigger the error message. In such case, you want to inspect the conditions of the Transmission speed sensor (TSS), Transmission fluid temperature sensor (TFTS), Throttle position sensor (TPS), Vehicle speed sensor (VSS), and Transmission range sensor(TRS).

4.  Transmission system Malfunction:

The transmission system plays an important role in the gearing process. You want to make sure you inspect for malfunctions. You should check for mechanical problems in the system, worn-out gears, damaged transmission control modules, and others that could trigger the warning.

How to Fix the Service Required: Do Not Shift Gear?

Fixing the “Service Required: Do Not Shift Gear”  message depends on what triggers the error message. Before proceeding to the fixes methods, we recommend learning how to reset the error message when it appears on your cluster display.

How to perform a transmission reset on your Mercedes Benz?

This reset method will work for most Mercedes Benz, especially vehicles with the 5-speed gearbox (722.6) and the 7-speed gearbox (722.9). Let’s proceed:

1. Turn the key in the ignition to position 2. Do not start the car.
2. Press the Gas pedal down for 10 seconds
3. Turn the key back to position zero and gently release the gas pedal. Note, do not remove the key from the ignition
4. Wait for at least two minutes While the key is still in the ignition.
5. Start the car, as the transmission is already reset.
6. Go ahead and drive the vehicle for at least 15 minutes. It allows the transmission to re-learn from scratch.

Steps to fix the Transmission error message of Cluster display

Step 1: Diagnose the issue

You want to diagnose the cause of the error message accurately. It might involve physically inspecting some components and using an OBDII scanner to see stored code.

Step 2: Fix the root cause

After identifying the root cause, you want to fix the cause. You can take your vehicle to a professional mechanic if you lack the requisite skill to make the fix. These include

• Replacing or repairing the transmission system if there is a mechanical fault in the transmission system.
• Updating software for cases of software glitches and malfunctions
• Adjusting and repairing the clutch.
• Replacing or fixing sensors that can affect the gear shifting.
• Replacing the auxiliary battery if it is damaged
• Filling the transmission fluid as at when due. 

Step 3:  Take your vehicle for a drive 

After making the required fix, we recommend taking your vehicle for a minimum of 15 minutes drive to ensure the problem is fixed and does not reoccur.

Final Word! 

The service required error message can be confusing and sometimes tempting to neglect. We always recommend making a timely effort to fix your car to prevent further damage. Don’t be afraid to seek professional help if you cannot fix the error message yourself.