You are driving and all of a sudden you get an error message "Drive to Workshop without changing gear".
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.
In other cases your vehicle won't start because the engine doesn't crank at all.
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.
Common symptoms of a defective ISM module include
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.
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.
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:
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.
The intelligent servo module for DIRECT SELECT is mounted on the left side (driver side for LHD) on the transmission housing.
ISM module receives input from the gear selector. ISM also communicates via C.A.N. with the following modules.
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.
Most 2006 and newer vehicles that are equipped with 7-speed transmission 722.9, such as:
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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.