I know trunk lid open/close problems have been discussed numerous times in many posts, but I believe this one is a bit unique. Replaced the PSE Pump after diagnosing that none of the remote actuated stuff worked. Replacing the PSE Pump brought back to life all remote functions (doors, soft-close, trunk unlatch, etc.). The only thing that didn’t come back was the automatic assist opening of the trunk lid. In essence, the trunk can be unlatched remotely and the lid jumps a tad as the lock is disengaged. However, the lid does not rise and must be lifted manually. Of course, it’s very stiff. Pressing the red ‘trunk close’ button has no effect.

In all cases the hydraulic pump on the right, directly next to the battery, makes no sound. Bad hydraulic pump? Doubtful, as a voltmeter confirms there is no power whatsoever going to the hydraulic pump when the red ‘trunk close’ button is depressed. If I press the ‘trunk open’ button on the remote key, the PSE pump comes to life and unlatches the lock, but the hydraulic pump fails to energize. This is what I think is unique about this problem.

So we look for blown fuses. The Fuse Chart indicates 3 fuses of interest – F13, F57, F62. On the sheet these are listed under “Remote closing and locking trunk lid” and “Remote trunk lid release”. All 3 fuses ohm out correctly. To my thinking, there must be some sort of relay that controls the direction of the hydraulic pump rotation as the hydraulic pump motor only has 2 wires (black and white), suggesting a bi-directional motor. However, the fuse chart does not list any relays associated with the trunk. So I have a couple questions:

1) Is there another mystery fuse somewhere that controls the trunk lid opening/closing hydraulic pump (not the PSE Pump)? Fusible link, maybe?

2) Where are the directional control relay(s) for the trunk lid opening hydraulic pump? There are two small relays very near the pump’s electrical connection, but it’s unclear if these are related to the trunk lid open/close pump.

I doubt it’s the infamous trunk lid latch actuator since this has (to my knowledge) no effect on energizing the trunk lid assist hydraulic pump. Any ideas?

Cheers,
Jeff

 

Dealer (MB of San Antonio) tells me this action is normal after changing the PSE Pump and that the trunk open/close assist sequence needs to be reset. They are willing to perform the reset... for US$99. Anyone have the reset procedure or can shed light on the subject?
Cheers,
Jeff

 

Problem solved. In fact, there was a rev change on the PSE Pump that requires a reinitialization of the PSE sequence. The closing-assist function of the trunk lid is tied to the PSE circuit for safety reasons. Unclear as to why.

The fix was simple; connect to STAR and reinitialize the PSE circuit. Interestingly, the trick of holding down the remote trunk open/close switch in the driver's door does for 5 seconds does not work with the newly rev PSE Pump! Reinitialization is the only fix. BTW, the local dealer reinitialized the system for me at no charge.

Cheers,
Jeff

 

Out of curiosity would you happen to know the part number on your broken PSE pump and the one you replaced it with. I just purchased a PSE pump part number 220 800 12 48 and was wondering if all the features would still work on the vehicle. The one i removed from the car was 220 800 11 48 according to MB they 12 48 is the older model..

Thanks

 

Same as you; I removed 220.800.11.48 and installed 220.800.12.48. The 12.48 version is the newer rev, though I do not know what is upgraded in the pump assembly. For my S55, the new PSE Pump required a reinitialization through STAR. All functions work perfectly and the new pump is both silky smooth and quiet. No problems.
Cheers,
Jeff

 

Sweet thanks man, I was able to grab it for a bargin $90 :P

 

Bear in mind that my PSE Pump was new and out of the box from MB. A pre-owned unit may not operate identical to new, for one reason or another. Also, the guts of an old unit will fit precisiely in the housing of a new part number. Just something to keep in mind. Caveat emptor. At a minimum, you'll have to re-initialize the soft-close circuit through STAR, which will cure the trunk close-assist problem.
Cheers,
Jeff

 

Thanks brother, Also got the follwing reply from MB

"Dear Mr. Perez:

Since 220 800 11 48 is no longer available 220 800 12 48 is approved by Mercedes-Benz as a replacement for the prior part on any repairs the prior part would be required.

We apologize for any confusion and recommend you speak to the parts department at your local authorized Mercedes-Benz dealer if you are still uncertain about the part.

Maria"

 

Gents. S500 2003. My trunk assist has been groaning up and down to a point it is embarrassing in a parking lot. I am pretty handy and enjoy such projects but don't know where to start on the cure. I don't trust the service advisors and if it's a simple part or rebuild kit I am up for that. Trunk struts aren't the problem as they seem to hold any position with ease. I actually think a valet parking attendant forced the trunk and may have damaged. Any help appreciated.

 

Your problem may be the trunk hinge. See a previous thread where I posted this.

 

i have 2002 S500 with "Designo" Package.

"MERCEDES S500 Vacuum Supply Pump For Remote TrunkLocking Pull down see pic attached)

I need to know how you can open the lid (I just call it) andput fuel (my understanding it should be light hydraulic oil), I did open thesteel strap and till can’t pull out lid

 

Hi everybody. My PSE Pump packed up and MB South Africa want SAR 10000 (US$ 660) for a new one (Ridiculous). I took it apart and found it was the motor (13 years) decided to be tired, but the rest of the unit was intact and not "Melted" due to overheated air from the pump. With some searching I found in the US a supplier of the motor only (King Motor) and I ordered one for ~ SAR 400. The replacement is very easy (Disassemble pump fro motor and reassemble with new motor). This way a "Reset" is not required either as the electronic "Memories" remain as is. Saved me a pack so to say and one learns more about inner working of ones car.

 

So about $30 usd? Sweet!!