Classic Mercedes Benz diagnostics, consultations, inspections
One of the nice features W140 S-class Mercedes Benz has is door and trunk closing assistance. Once door is latched and trunk pushed to close electric pump pulls it in. As vehicles age, many pumps start failing leaving owner slam doors and trunk to close them fully. Most likely that is caused by a faulty close assist pump.
In most cases, drivers door fails to close itself first as it’s used the most. Many people reset the pump by pulling the fuse #9 out trunk fuse panel. After some time the pump stops operating again because the problem is not repaired with reset. There are few things that can go wrong: vacuum leak inside door or trunk close assist mechanism, leaking vacuum connections on pump or actuators, leaking vacuum hose, pump out the adjustment internally, pump valves leaking, shut off valve leaking, and pump motor failure.
In most cases, if one of the doors or trunk stop working, but other doors still work pump pressure needs adjusting. Usually I adjust the pressure in the pump. Then I connect it my car and fine tune pressure adjustment. Then I run the pump many cycles to warm it up to see if the motor operates properly. That is the first step in troubleshooting close assist system. Sometimes after running the pump for few cycles other issues show up and need to be corrected.
If your pump stops operating after every fuse #9 reset, then you might have an other pump failure and simple adjustment might not fix it. Let me know your symptoms and we can take it from there.
Below is the video of soft close pump testing on my car
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