Mercedes-Benz owners may get an error message on the dashboard that states, "Drive to Workshop without changing gear."
The most common problem that causes Drive to Workshop Without Changing Gear on a Mercedes-Benz is a faulty Intelligent Servo Module (ISM), also known as component A80.
On the older models, all Mercedes-Benz vehicles used to have a mechanical link between the shifter and transmission; that's no longer the case for models equipped with the 7-speed and 9-speed automatic transmissions.
In most MB vehicles, the gear selector is mounted on the steering column and no longer has a mechanical link to the transmission.
Around 2005, Mercedes-Benz introduced the 722.9 New Automatic Gearbox 2 (NAG2) automatic transmission, which no longer has a mechanical link between the shifter and transmission. Instead, Mercedes-Benz started using drive-by-wire technology.
This is known as drive-by-wire technology.
Instead of a mechanical link to the transmission, you select gears electronically, and the Intelligent Servo Module (A80) or ISM selects the transmission gear position.
Replacing the ISM unit at the dealership can be very expensive. The cheaper solution is to remove and fix your existing ISM module.
Don't expect a Mercedes-Benz dealer to repair your existing ISM or install a used ISM. Dealerships will only replace faulty ISM with a new unit. You may even get told that a used ISM module is married to the car and can not be resued, but that is no longer true as many specialized auto repair shops can make a used ISM virgin and pair it to another vehicle.
If you decide to fix your faulty ISM module, you will need to raise the vehicle to remove the module mounted on the side of the transmission housing. ISM module is mounted on the outside of the transmission, so the transmission itself does not need to come off.
ISM can then be sent to a Mercedes-Benz specialist who will repair or flash your VIN. You can find several Mercedes-Benz specialists on eBay that offer Mercedes-Benz ISM Flash / Repair Service.
Even though in the majority of cases this error means faulty ISM module, we recommend to read the fault codes with a Mercedes-Benz scanner or have an auto mechanic diagnose the vehicle to confirm the ISM is defective.
First, let's take a look at common symptoms of a defective ISM module, include
- The 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 it is in Park on Neutral.
- Drive to the workshop without selecting gear on the dashboard
- 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.
- The engine runs at high rpm.
- Error communicating with Actuator Motor A80 of Intelligent Servo Module
These problems can be caused due to either ISM software issues or hardware failures.
Common fault codes that are triggered by a faulty Intelligent Servo Module (ISM A80).
- 1994 - Component A80 Direct Select Defective / Can not reach the specific gear target position
- 1984 Unkown fault code
- 5399 ESP CAN Signal Gear Selected from N15/3 implausible
- C103-ETC No CAN Message Received from A80 (Intelligent Servo Module) for direct selection.
The best way to find what is wrong is to have your mechanic or yourself scan the ISM with an advanced Mercedes-Benz scanner.
How to Diagnose ISM unit
To diagnose Mercedes-Benz ISM, you will need a Mercedes All System Scanner.
- Connect your scanner to the diagnostic port under the dashboard.
- Allow your scanner to turn on.
- Select Mercedes-Benz, then your Model.
- Select Control Units
- Select option 1. It will be labeled Powertrain or Drivetrain
- Select the ISM - Intelligent servo module for Direct Select.
- Once you enter the ISM module, you will be able to:
View software/hardware version
Read Fault Codes
Clear Fault Codes
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 of why your Mercedes-Benz won't drive or is stuck in the 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
It is possible to repair your existing ISM module. Repairing or flashing a used 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 on eBay.
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 to carry the initial adaptation 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 that show these fault 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.
How much does it cost to replace an ISM module at Mercedes-Benz dealership?
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. You will spend anywhere from $1200-$1900 to replace and program the ISM at the dealership or repair shop.
If you use an independent mechanic, they will have to order the ISM module from Mercedes-Benz. You will need to provide proof of vehicle ownership and identification. Mercedes-Benz requires this information.
Once the order is approved, the mechanic receives the ISM Module. The module will need to be replaced. Also, the ISM will have to be programmed with a professional scanner.
Where is the ISM module located
The intelligent servo module for DIRECT SELECT is mounted on the left side (driver side for LHD) of the transmission housing. The vehicle needs to be raised to access the ISM module but the transmission itself does not need to be removed.
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 automatically switches 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
Mercedes Intelligent Servo Module (ISM) is installed in 2005, and newer vehicles are equipped with the 7G Tronic Transmission (Code: 722.9) and gear selector mounted on the steering column. Except for a few 2005 to 2007 models that still use the 5-speed 722.6 transmissions.
All 2006 and newer vehicles that are equipped with 7-speed transmission 722.9 have an ISM module. For example:
|MODEL||YEARS||COUNTRY||TRANS TYPE||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 use ISM, install it in 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. Several vendors offer Mercedes ISM Renew service on eBay.