'91 LS400, trunk will not open. key will not turn, electric latch switch clicks but won't open. valet lock in open position. Tried 1) disconnect battery, reconnect battery, use switch, push down on trunk and then pull up 2) locked valet button and reopened 3) key in trunk lock but won't turn in either direction 4) 2nd person held switch open while I pushed and pulled on trunk 5) sprayed WD40 in lock key hole several times. Nothing has worked so far. Taking out back seat doesn't seem to be option. Read a post where guy drilled 3/4" hole behind license plate to gain access to cable but not ready to do that yet. Any other ideas???

There could be several reasons why the trunk of your 2004 Mercedes-Benz S500 will not open. Here are a few things you can try:

1. Check the latch: Make sure the latch is not stuck or damaged. You can try lubricating the latch with penetrating oil or WD-40, or gently prying it open with a flat tool like a screwdriver.
2. Check the trunk release button: If the trunk release button is not working, it may be due to a problem with the electrical system or a faulty trunk release switch. You can try replacing the fuse for the trunk release or checking the switch for any visible damage.
3. Check the key: If you are using a key to unlock the trunk, make sure the key is not damaged or worn out. You may need to have the key replaced if it is no longer functioning properly.
4. Check the trunk lock: If the trunk lock is stuck or damaged, it may be preventing the trunk from opening. You can try lubricating the lock with penetrating oil or WD-40, or have a locksmith inspect and repair the lock.

If you have tried these steps and the trunk is still not opening, it is possible that there is a problem with the trunk mechanism itself. In this case, it is recommended to have the car inspected by a mechanic. They will be able to diagnose the problem and recommend the appropriate repairs.

Have you got the valet switch turned on?

Unlock door with valet key to shut alarm off and remove the trunk release switch. Jump the trunk switch wires together for a second and it will open

Valet Key ? 0nly does the drivers door & ignition

Lower the back seat and crawl into the trunk and see what the latch is doing when you activate the key fob. the trunk lid will have to be open to enable any repairs. Also an emergency release cable is probably visible (yellow handle) inside the trunk and will Open the trunk lid.

check trunk fuse

There are 3 phases to fixing your car's trunk lid release problem.

Phase 1: First check the fuse - once you know that's OK, then proceed to phase 2 (below).
The fuse for the trunk lock is
the bcm (pwr) 15A fuse in the instrument panel fuse box (behind panel at drivers right foot)

Check that fuse, as it is the power supply for the button on the dash that sends power to the actuator in the trunk.

Phase 2: Get the trunk open (without taking it to the dealership).
If you have remote keyless entry to the trunk, you could try that - but with the actuator
dead/dying, it shouldn't work.

Here are a couple of ideas to try to enter trunk while (a) actuator isn't working, and (b) all
valet lockout features (designed to deny valets access to the trunk) are in the "Lock" position:

There is the lock cylinder, which you stated is not functioning - put the key in, and it doesn't
turn. Just to be sure, consider: lubricate key with Graphite lock-type lubricant, and retry.

The trunk has 2 valet safetys...the locking rear seats which require access to the trunk to unlock, and then there is a valet switch in the trunk that locks the button on the dash from working to keep valet parking attendants out of the trunk. That may be in the lock position.

You can try accessing the center area of the fold down rear seat and see if you can unhinge the rear seat from there. Maybe reach in with your hand, or an extension-type tool.

there may be a way to fold the hinge away from the seat back so it can be removed from the hinge and give you access to the safety latch in the trunk and open it that way (white handle in trunk).
The white-handled safety latch release is desiged to prevent accidentally trapping children, and
if you can pull it with your extending-type or grasping-type tool, the trunk will open whether or
not the actuator motor is working.

Phase 3: Replace the Problem part.

Your failed part may be either (1) Trunk Release Relay, or (2) Trunk Lock Release Switch

My Satrun ION manual doesn't cover either of these parts, and the online parts houses, e.g.
http://www.rockauto.com/catalog/x,carcode,1431624,pgname,Electrical-Switch%2B%2526%252338%253B%2BRelay,a,search.yahoo.com%2BSearch%2Bfor%2B2004%2BSATURN
fail to provide instructions. One of those times a mechanic has to t=rely on his/her native
handiness and/or experience.
To identify which of these parts is bad, locae the Trunk Release Relay (call your dealer parts
dept. for helpful tips on finding it), then operate the dashboard trunk release button with your
ear close tothe relay - if it makes a noise, the problem is the Trunk Lock Release Switch in
the trunk lid, otherwise its the relay.

1. Open trunk
2. Place latch in lock position
3. Pull inside trunk release to see what isn't moving
4. If trunk key won't turn, the key may be worn out and need to be replaced

does the key turn the trunk lock?if not theres one issue right there.the other may be that the valet lever on trunk latch assy. may have inadvertantly been engaged if deck lid was slammed closed.the release solenoid will make noise when activated by fob or lever in car but because of valet being engaged cannot release latch.does key unlock glovebox?if not this may also be a valet key cut.contact nissan dealer to cut regular key.ive seen the slamming the deck lid scenario a million times as the valet lever takes hardly any effort to engage.good luck and let me know how you make out.