Checking automatic transmission solenoids on Mercedes-Benz cars
Tools and Equipment:
* OBD2 diagnostic scanner
* Multimeter
* Wrench set
* Candle key
* Set of open-end wrenches
* Tool for removing transmission oil bath
Procedure:
1. Preparation:
* Turn off the engine and let the car cool down.
* Place the vehicle on a level surface and apply the parking brake.
* Disconnect the negative terminal of the battery.
2. Reading fault codes:
* Connect the diagnostic scanner to the OBD2 connector of the car.
* Turn on the ignition, but do not start the engine.
*Read any stored trouble codes related to the automatic transmission solenoids.
3. Visual inspection:
* Open the hood and find the automatic transmission control unit.
* Inspect wires and connectors for damage or corrosion.
* Remove the connector and inspect the contacts for dirt or damage.
4. Checking the resistance of the solenoids:
* Disconnect the solenoid connector from the automatic transmission control unit.
*Using a multimeter set to the ohms range, measure the resistance between the solenoid connector pins.
*Compare the measured resistance with that specified in the repair manual for that solenoid.
* If the resistance is out of range, replace the solenoid.
5. Checking solenoids for short circuit:
* Set the multimeter to the short circuit or continuity measuring range.
* Connect one multimeter probe to the solenoid connector terminal.
* Connect another dipstick to engine ground.
*If the multimeter beeps, it indicates a short circuit.
* Replace the solenoid.
6. Solenoid open circuit test:
* Set the multimeter to the continuity measurement range.
* Connect one multimeter probe to the solenoid connector terminal.
* Connect another probe to the positive terminal of the battery.
*If the multimeter does not beep, it indicates an open circuit.
* Replace the solenoid.
7. Cleaning and restoration:
*If the solenoid has dirty or oxidized contacts, clean them with contact cleaner and a brush.
*If possible, disassemble the solenoid and clean the internal components with carburetor cleaner.
* Reassemble the solenoid and test it again.
8. Assembly:
* Reinstall the solenoids and tighten them using the appropriate tool.
* Connect the wiring and connectors.
* Install the connector on the automatic transmission control unit.
9. Clearing fault codes:
* Connect a diagnostic scanner and clear all stored trouble codes.
10. Test drive:
* Start the engine and let it idle for a few minutes.
*Take a test drive to check transmission operation.
Note:
*If automatic transmission problems persist after replacing the solenoids, further diagnostics and repairs may be required.
* It is recommended that you have your automatic transmission solenoids inspected and repaired by a qualified mechanic.