Before continuing, let’s make sure we are talking about the correct unit. Sometimes it is called an electronic control unit or ECU.
When it is determined that the Mercedes engine control module (ECM) has failed then it is time to replace it. The first step is to check online for the best opportunity is to pay for a rebuilt Mercedes ECM. Each ECM is mated electronically to the vehicle. When you buy a rebuilt ECM, you ship your current ECM out, have it rebuilt and reprogrammed, and then they ship it back. This can save you a lot of money, rather than having to go straight to the dealer.
Inspect the sensors
Sometimes a voltage spike will have passed through the ECM and also damaged one or more vehicle sensors. You will need to inspect the sensors, which are often done using a volt-ohm meter. Check each sensor for any damage. Clean off the connections of the sensors as needed. If all are well continue on to the next step.
Check the Replacement Part
If the replacement part indicates a need to flash the ECM before installation be sure to do so. If you are unsure or unable to do this step bring it to a qualified mechanic. Otherwise, continue with the next step.
Find the Case
Depending on the model of Mercedes car, the electronics case is typically located near the battery, often in the back-right corner, as you face the car to replace it. Remove the case lid by turning the plastic tabs.
Find the ECM
It will be located at the closest point in the case, after you open it. There you will notice four leads plugged into the ECM. Push in the lever of each lead and then remove the lead. Once you have all four removed from the ECM you can extract the engine control module.
Replacing the ECM
Be sure to clean the parts and shake the leads to remove any debris. Once satisfied, insert the ECM into the case and secure it down. Each lead has a unique fitting so as to not confuse the appropriate lead. Smoothly insert and clamp down each lead.
Test the ECM
Scan the computer for any trouble codes. If a trouble code does appear then you will need to respond accordingly. If none appears then continue on to the next step.
Start Your Vehicle
If the vehicle starts without any apparent symptoms or Check Engine Light then turn off the car. Re-place the lid onto the electronics case and secure it.
The process to replace the ECM should be complete. Continue to monitor the performance of the vehicle until satisfied with the repair. Congratulations, you have successfully repaired your vehicle!