Tools and materials:
* OBD-II scanner
* Multimeter
*Torx T25 screwdriver
* Dipstick
Instructions:
1. Connect the OBD-II scanner to the vehicle’s diagnostic port.
* It is usually located under the steering column or in the interior under the dashboard.
2. Turn on the ignition, but do not start the engine.
3. Enter Transmission Diagnostic Mode.
*This procedure may vary depending on the Mercedes model. This usually starts with accessing the diagnostic menu through a key combination on the dashboard or steering wheel.
4. Check fault codes.
* The scanner will display any fault codes that the automatic transmission control module (TCM) has. Write them down for future troubleshooting.
5. Check the automatic transmission operating parameters in real time.
* Real-time data such as engine speed, throttle position and transmission fluid temperature can help identify potential TCM problems.
6. Turn off the ignition and disconnect the battery.
* This is required for secure access to the TCM.
7. Find TCM.
* Usually the TCM is located either inside the automatic transmission or in a separate housing under the hood.
8. Remove the TCM.
*This may require removing T25 Torx bolts.
9. Check TCM connectors.
* Inspect the connectors for dirt, corrosion or damage. Clean or replace connectors as necessary.
10. Check TCM wiring harness.
*Trace the wiring from the TCM connector to the automatic transmission and other components. Look for signs of breaks, kinks, or damage to the insulation.
11. Check TCM power supply.
*Using a multimeter, check for power to the TCM at the power terminals. This is usually a black or red wire.
12. Check TCM ground.
*Check for a solid ground on the TCM at the ground terminal. This is usually a black wire with a white stripe.
13. Check the transmission fluid level.
* Using the dipstick, check the transmission fluid level. Low fluid levels can cause overheating and damage to the TCM.
14. Reinstall the TCM and battery.
* Connect the battery and tighten the T25 TCM Torx bolts.
15. Scan the vehicle again for trouble codes.
*Erasing previously stored trouble codes and scanning the vehicle for new codes can help determine if the problem is resolved.
Additionally:
*If the TCM fails, it may need to be replaced.
*Replacing a TCM may require reprogramming or coding a new TCM to work properly with the vehicle.
*Always refer to your specific Mercedes model repair manual for specific information and procedures.