Weird DTC codes (PSE) ---check your battery!!!
 

Weak or sulfated car batteries can cause strange problems in any car, the W220 is no exception.

Here's one example. Basically, the ECU throws a code every time the PSE pump engages to lock/unlock doors when the engine is off. It will NOT throw any codes when the engine is running and alternator is putting out at steady 13.8-14.2V.

I started this thread in response to something @wallyp wrote here: http://www.benzworld.org/forums/w220...odule-dtc.html

So I decided to do a little more checking with my MBII, and the results I get are repeatable. Engine off; actuate the PSE to lock/unlock doors and the next time you check the PSE module, the 8 DTCs appear. Clear the codes, turn the engine on and try the same thing. Only variable that's changed is that the alternator is spinning and charging the battery. The result? No DTCs. Did this over several times just to be sure, and I'm pretty certain it's due to the 3+ year old battery in the trunk. My smart 12V charger actually reported the battery as being sulfated so it's certainly time for a replacement.

The moral of the story? Weird electrical stuff shows up; check your battery voltage!!! Anything less than 12.4v after 24 hours needs additional diagnosis and possible replacement.

Here's a good PDF resource that explains the above in a bit better detail:
https://www.euromotoelectrics.com/v/...0diagnosis.pdf

Hope this helps.