Troubleshooting a Mercedes Transmission

1. Check your valve hoses. The valve hoses in the Mercedes engine are located in a small black box on top of the valve cover. Check the tops of the valve covers to make sure they are not worn out; if they are, you will need to replace them.
2. Look at the color of the transmission fluid. Transmission fluid needs to be flushed and changed frequently, and the fluid is a deep cherry red in color. If it has become black or turned a dark gray, there could be an internal oil leak that is affecting your transmission.
3. Look at your transmission oil pan. A mechanic may need to remove this for you; if there is metal at the bottom of your transmission oil pan, the transmission will have failed.
4. Check your vacuum modulator. This part is responsible for telling the transmission when to shift. If it is not adjusted properly, you may experience an 'early shift' or 'late shift.' Shift slips can be adjusted by turning the modulator clockwise to increase the pressure and initiate a later shift, or counterclockwise to lower the pressure and initiate an earlier shift.
5. Change your throttle pressure. Another way to adjust how the transmission shifts is by increasing or decreasing the tension of your throttle pressure cable. Make the slide shorter to make the transmission shift later, or make it longer to make it shift earlier.
6. Listen to the engine while it idles. An unstable idle or 'growling noise' could be a sign of a poor intake air temperature sensor, bad engine coolant temperature sensor or a dirty throttle body. Make sure all these components are working properly to prevent transmission damage.