Mercedes ISM Problems Explained (Intelligent Servo Module)

You are driving and all of a sudden you get an error message "Drive to Workshop without changing gear".

Mercedes Visit Workshop without changing gears
Mercedes-Benz S-Class S550 Error "Visit worthshop without shifting gears"

In another scenario you may get stuck in a parking lot or home because your Mercedes-Benz refuses to shift gear from P to R, N, D.

Mercedes Stuck in Park

In other cases your vehicle won't start because the engine doesn't crank at all.

Mercedes wont start

Intelligent Servo Module (ISM) failure is often the culprit that causes these problems.

Mercedes Intelligent Servo Module (ISM) is installed on 2004 and newer vehicles equipped with the 7G Tronic Transmission (Code: 722.9) and gear selector mounted on the steering column.

Replacing the ISM unit can be very expensive. Repairing the existing ISM is possible and much less costly.

Don't expect your dealer to repair your existing ISM, dealerships only replace the bad ISM with a new unit. You will need to find a Mercedes expert if you want to fix your existing ISM.

It is crucial to get the vehicle properly diagnosed and confirm the ISM is defective.

This guide will help you learn how to diagnose ISM problems but we strongly recommended you have a Mercedes-Benz mechanic verify your findings. 

Symptoms

Mercedes-Benz shifter not responding

Common symptoms of a defective ISM module include

  • Car won't shift gears. No P, R, N, D.
  • Vehicle may not start, no crank-.The ISM (intelligent servo module) is responsible for the transmission gear position. It will prevent the car from turning over if it does not recognize that the car is in Park on Neutral. 
  • Drive to the workshop without selecting gear
  • the car would not change gears
  • Error message: The actuator motor in the component A80 ISM (Intelligent Servo Module) for Direct Select cannot reach its specified target position.
  • Shifter becomes unresponsive.

These problems can be caused due to either ISM software issues or hardware failures. The best way to find what is wrong is to have your mechanic or yourself scan the ISM with an advanced OBD-II scanner

How to diagnose ISM unit

Diagnose mercedes ISM mdoule problem car won't shift go in P R N Drive

To diagnose Mercedes-Benz ISM you will need a scanner such as MB Star Diagnostic or another professional level scanner such as Autel MaxiDAS.

  1. Connect your scanner to the diagnostic port under the dashboard. 
  2. Allow your scanner to turn on. 
  3. Select Mercedes-Benz then your Model. 
  4. Select Control Units
  5. Select option 1. It will be labeled Powertrain or Drivetrain
  6. Select the ISM - Intelligent servo module for Direct Select. 
  7. Once you enter the ISM module you will be able to: 
    • View software/hardware version
    • Read Fault Codes
    • Clear Fault Codes
    • Data Stream
    • Activation - Move transmission into Neutral Position

 

When you scan the ISM module, you will get fault codes such as 1994 - Component A80 (intelligent servo module for Direct Select) is defective. 

Once you scan the codes, you will have a better idea why your Mercedes-Benz won't drive or is stuck in park. Make sure to scan all the control units to ensure no other issues are present. 

If your Mercedes-Benz has a defective ISM module, it will either need to be repaired or replaced. 

Repair Mercedes-Benz ISM unit

Repair Mercedes ISM Module Location

It is possible to repair your existing ISM module. Repairing the ISM module is much cheaper than replacing it. 

You will need to remove the ISM module from the vehicle and ship it to a vendor that offers ISM module repair.

A technician repairs your ISM module and ships it back. The total turnaround time ranges between 5 to 12 days, depending on your location and the service provider you choose. 

In addition to the low cost, another advantage of repairing your ISM module is that it will not need SCN coding. SCN coding is required when you install a new ISM module. During SCN coding the VIN is permanently coded to the ISM module. 

You will still need a professional scanner though to carry initial adaptation or also known as the Selection Sensor Adaptation procedure. This can be carried out with MB Star Diagnostic Tool or with professional-level scanners. 

Keep in mind that some modules can not be repaired. There is no way for you to know if your damaged ISM module can be fixed or not until the technician tests it. 

Generally speaking ISM modules with these codes can be repaired: 

  • Error: 1984; Description: Uknown fault code Unknown Fault Type : -1
  • Error1994; Description: Component A80 ( Intelligent Servo Module for Direct Select) is defective
  • Error 1904 - cannot be cleared

Replace Mercedes-Benz ISM unit

Any Mercedes-Benz dealership or an independent mechanic that specializes in Mercedes-Benz cars can replace your ISM. 

Getting the ISM replaced can be an expensive repair. At the dealership or repair shop, you will spend anywhere from $1200-$1900 to replace and program the ISM.  

If you use an independent mechanic they will have to order the ISM module form Mercedes-Benz. You will need to provide proof of vehicle ownership and identification. This information is required by Mercedes-Benz.

Once the order is approved, the mechanic receives the ISM Module. The module will need to be replaced. In addition, the ISM will have to be programmed with a professional scanner. 

Frequently Asked Questions

Where is the ISM module installed? 

Location of Mercedes-Benz ISM Module

The intelligent servo module for DIRECT SELECT is mounted on the left side (driver side for LHD) on the transmission housing. 

ISM Communication

ISM module receives input from the gear selector. ISM also communicates via C.A.N. with the following modules. 

  • The instrument cluster (A1)
  • ESP control unit (N47-5) - Vehicle speed input. Needed to P release or D engage. 
  • EIS [EZS] control unit (N73) - Input from EIS is used to automatically switch the vehicle into P when the car is turned off. 
  • Steering column module (N80)
  • The central gateway control unit (N93)
  • Fully integrated transmission control (VGS) control unit (Y3/8n4) 

For example, vehicle speed input is needed to engage D or release Park and is received from the ESP module.

When the vehicle is turned off information is required to switch transmission automatically to Park and is provided by the EIS. 

Which Mercedes-Benz vehicles have ISM? 

Most 2006 and newer vehicles that are equipped with 7-speed transmission 722.9, such as: 

MODEL YEARS COUNTRY TRANSTYPE ENGINE TYPE/SIZE TRANS MODEL
MERCEDES A CLASS 00-11 CHN EGY DEU MYS ZAF VNM 7 SP R/AWD L4 2.2L V6 2.5L 3.0L 3.5L V8 6.3L W7A700
MERCEDES A CLASS 11-Jul EGY 7 SP R/AWD V6 3.0L V8 6.3L W7B700
MERCEDES A CLASS 11-Jul EGY DEU VNM 7 SP R/AWD V6 2.5L 3.0L 3.5L W7X550
MERCEDES CL 11-Mar DEU 7 SP R/AWD V8 5.0L 5.5L 6.3L W7A700
MERCEDES CLC 11-Aug BRA 7 SP RWD V6 2.5L 3.5L W7A700
MERCEDES CLK 9-Apr DEU 7 SP RWD V6 2.5L 3.0L 3.5L V8 5.0L 5.5L 6.3L W7A700
MERCEDES CLS 11-Apr DEU 7 SP R/AWD V6 3.0L 3.5L V8 4.6L 5.0L 5.4L 5.5L 6.3L W7A700
MERCEDES CLS 11-Oct DEU 7 SP RWD V8 6.3L W7B700
MERCEDES E CLASS 11-Feb CHN EGY DEU IND IRN MYS THA VNM 7 SP R/AWD L4 2.2L V6 2.5L 2.6L 3.0L 3.5L V8 4.0L 5.0L W7A700
MERCEDES E CLASS 11-Sep DEU 7 SP RWD V8 5.5L 6.3L W7B700
MERCEDES E CLASS 11-Sep DEU 7 SP R/AWD V6 3.0L 3.5L V8 5.5L W7X550
MERCEDES G WAGON 11-Jun AUT 7 SP AWD V6 3.0L V8 4.0L 4.6L 5.5L W7A700
MERCEDES GL CLASS 11-Jun USA 7 SP AWD V6 3.0L V8 4.0L 4.6L 5.5L W7A700
MERCEDES GLK 11-Aug DEU 7 SP R/AWD L4 2.2L V6 3.0L 3.5L W7X550
MERCEDES GLK 11-Sep DEU 7 SP R/AWD V6 3.0L W7A700
MERCEDES ML CLASS 11-May USA 7 SP R/AWD V6 3.0L 3.5L V8 4.0L 4.6L 5.0L 5.5L 6.3L W7A700
MERCEDES R CLASS 11-May USA 7 SP R/AWD V6 3.0L 3.5L V8 4.6L 5.0L 5.5L W7A700
MERCEDES S CLASS 11-May EGY DEU IND IDN MYS THA 7 SP R/AWD L4 2.2L V6 3.0L 3.5L V8 4.0L 4.3L 4.6L 5.5L W7A700
MERCEDES S CLASS 11-Jun DEU 7 SP R/AWD V6 3.0L 3.5L V8 4.6L 5.5L W7X550
MERCEDES SL 11-May DEU 7 SP R/AWD V6 3.0L 3.5L V8 5.0L 5.5L W7A700
MERCEDES SL 11-Jul DEU 7 SP R/AWD V8 6.3L W7B700
MERCEDES SLK 11-May DEU 7 SP R/AWD L4 1.8L 2.2L V6 3.0L 3.5L V8 5.4L 5.5L W7A700
SSANGYONG CHAIRMAN 11-Aug PRK 7 SP R/AWD V6 3.2L 3.6L V8 5.0L W7A700

Can I install a used ISM? 

ISM module is locked to your vehicle. You can not take a used ISM, install it on your car and expect it to work without first coding it. 

The only way to get a used ISM to work on your Mercedes-Benz is to find a third party that can Program ISM Module. This procedure may be referred to as flashing ISM or as ISM RENEW.

During ISM flashing the old VIN is erased from the ISM. The ISM is thus made virgin then your vehicle VIN is coded to the used ISM.

By YOUCANIC on Sep 20, 2019

Vehicle

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