My 2002 S500 W220 suddenly refused to "pop" the trunk.

I dug out the physical key and was able to open the trunk to get the groceries out, but it also refuses to assist when closing the trunk.

There are plenty of posts here about how this works on the older chassis, but I don't see much on the newer cars about this.

I hear a subdued "thunk" when I hit the release button, but nothing on the mechanism appears to even be trying to move to open the latch.

I'm not sure where to start on this to see if it is the release mechanism, or a problem with the vacuum pump...

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02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)

Most likely a code in the PSE system causing the problem, a trip to technicain to read codes from system.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

The only "current" code was a "Timeout"
The codes were cleared and it still didn't work.

Does this have a separate pump just for the trunk lid?
(EDIT: No, the pump provides assist for the doors as well.)

__________________
02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)

Ok, I have disassembled the latch mechanism and mostly understand how it works.

It uses air PRESSURE to operate and not Vacuum!

It would appear that I have no air pressure coming from the pump.
I can make the actuators function if I apply a small amount of pressure from my air hose.

Now, where is the pump? Is it just for operating the trunk? The door assist mechanisms still work just fine.

Where would the fuse for the pump be? I don't see a fuse box in the trunk.

__________________
02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)

The PSE pump does all pneumatic operations of the car. locking, closing assist, trunk, & seat lumbar functions.

Are you sure that codes are cleared?

PSE pump is in the left rear of the trunk

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

I have to agree with you that there must still be a code in the PSE that is inhibiting the line to the trunk mechanism.

If I manually apply pressure to the mechanism it will pull the latch to the fully closed position (off the car).

Likewise, pressure to the tube that feeds the release solenoid will un-latch it.

The problem can't be in the trunk lid unless a micro-switch is messing up.

Since these things (W220) are so code-sensitive I think the only thing I can do is put everything back together and let my shop re-read the codes and figure it out for me on Monday.

They dropped what they were doing this morning to read and reset the codes for me, but it seems we need to revisit that...

In my testing, I put a little too much pressure to the release diaphragm and cracked a few of the retainer tabs...

The part is 220-800-02-75 and it is only available from MB as the entire trunk latch assembly for $$$$. It is still holding together, and I will probably reinforce it with some epoxy, but I wonder if anybody happens to have one of these laying around in a latch assembly they have pulled off another car?

This W220 has been a pain. Multiple A/C problems, intermittent starter problems, rattling catalytic converter, and now this...


Thanks!

__________________
02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)

I still plan to take the car to the shop next week, but I've been testing things as I put the latch back together.

The epoxy I put on the un-lock pneumatic solenoid will hold just fine. It didn't come apart, it just cracked a couple of the retaining clips around the circumference.

UNLOCK MODE:

When I press the unlock button the electrically activated pneumatic valve clicks to route the pressure to the unlock solenoid, but it does not REMAIN engaged, and the pump does not engage to create pressure to activate the solenoid. If I apply a little pressure to the inlet and press the button, there is a little bit of movement in the solenoid when the electric valve engages, but because it disengages almost immediately, there is no unlocking action other than a little wiggle...

OBSERVATIONS:

Why does the electric solenoid disengage so quickly?
Why does the pump not engage and make a little pneumatic pressure?

PERHAPS THIS IS DUE TO A LOCKOUT CODE STORED IN THE PSE?


CLOSE ASSIST MODE:

When the latch is clicked to the first closed position, the pump engages, and there is some pressure felt at the pneumatic tube to the solenoid, but it is very weak compared to what is needed to activate closure. The pump runs for several seconds and stops, presumably with a timeout. In a couple of seconds the pump engages a second time for a couple of seconds with a different sound.

OBSERVATIONS:

Why is there not enough pressure generated from the running pump to activate the closure solenoid?

If I cover the tube from the pump with my finger and activate the closure cycle, the pump runs for the same amount of time. In theory, I'm thinking if it sensed the pressure had reached the specifications, the pump would have disengaged earlier...

In the closure scenario, I'm thinking there is either a leak in a hose that prevents the pump from reaching full pressure, or something in the pump is not creating the pressure in the first place.

The connectors at the pump are labeled. The one to the trunk latch is labeled "HECK". If I disconnect it at the pump and apply a little pressure to the tube with my air gun, it will READILY operate the close assist.


SUMMARY:
I'm thinking the pump has a problem... It DOES engage to close the trunk. It will hiss if the tube is disconnected while the pump in engaged, but doesn't seem to create enough pressure to operate the closure.

The unlatch mode isn't really trying, and I am guessing the stored code is preventing it from engaging.

If anyone has experince with this, please chime in. I will share my observations with my shop next week and we will go from there...

__________________
02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)

Well, it is back from the shop and it has a brand spanking new PSE controller.

All is well, other than my wallet, which should heal over time...

One observation about the new PSE is that now, when I operate the unlatch feature, it opens the trunk almost immediately. I have had this car for a year and a half, and have ALWAYS had to hold the trunk release for a second or two before it would activate.

Looking back, I would say that this was a warning sign that the pump was headed for trouble, but I thought this was normal!

I hope this thread is of use to others searching for information on how the trunk release works on this car.

__________________
02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)