My '99 S420 has been giving me trouble with the close assist feature for the doors. The trunk won't pull down and neither will the driver's side door. All of the other doors work fine. I tried pulling the two fuses for the system and the close assist works on all doors for about a week, then the trunk and driver's side door stop working again.

I want to test each door individually and was trying to find a way to pressurize them. Can I pull say the line for the driver's door from the pump and put pressure in the line from another source?

Thanks,
Dave

Had the exact same problem with my '94 S500 and it appears that your door is 'timing out.' Here's the site that helped me ALOT and ever since I followed the instructions posted there I had no more problems from any of my doors, or trunk lid. Hope this helps!!http://www.v12uberalles.com/Closing_Assist_Pump.htm