Help!! Can't open truck on 99 S320
 

I have a real problem. My truck will not open on my 1999 S320. For some reson the door/ignition key will not work the trunk lock. The trunk lock cyclinder may have been changed before I owned the car. Now the power lock system that works the door locks and trunk lock is dead so when you push the button on the trunk lid nothing happens. There has to be power to the lock mechanism in order for the push button to unlock it. The remote key can't open it, the switch on the dash to open the trunk doesn't work.

Anyone have a idea on how to get the trunk open or can you get inside the trunk by removing the back seat?

Thanks in advance.

I think that the vac pump for the trunk lock is under the rear seat. I would try that first. Get a mityvac and find the line for the trunk. Give it a few pumps and it should pop open.

Like ^

Also search this site for opening the trunk on a R129 SL 90 - 02 . There was a way that you could use a metal rod fished through a license plate bolt hole to pop the latch.

Given S class parts are cheap, you could cut through the tail light for access. Don't randomly cut / break as you don't want to damage the body or trunk trim. Also be sure you don't turn on any lights until you have the tail light plug removed.

Thanks for the suggestion. Bought a hand held vac and tried every line connected to the pump but none would unlock the truck. Then I noticed the gas cap door was latched after doing that. Now I couldn't refuel the car. (yikes)

So I took my air compressor and set the regulator down to about 30 psi and gently pressurized the line to the gas cap door. It opened! Then I pressurized the other lines until the truck push button was engaging and I could open the trunk. Turns out the vac pump for the central lock system is blowing its fuse, and of course that fuse is located in the trunk! Now trying to find out how to repair the vac pump or find a replacement.

30 PSI is very high, I'd expect the stock system to be sub 10 PSI. Anyone have a spec in the manual?

i used firm lung positive pressure as well as a baby snot aspirator on a 99 and 00 E320. the pressure needed was pretty low.

generally speaking, positive pressure to unlock. vacuum to lock in the w210

I had the regulator set at 30 psi and slowly opened the valve to add air until it unlocked. I'm sure the lock mechanism actuated at a lower pressure.

Still too risky. For the next time you need low pressure, turn the regulator to zero then very slowly increase the pressure until you get a slight bit of air coming out of an open hose.

The systems nylon tubing can handle much more than 30 PSI however the connections and bellows likely can't. Atmospheric pressure is ~ 14.7 PSI however the lock system can't generate a perfect vacuum so the effective pressure under vacuum will be less.

In other words when the pump is directing vacuum to the system, there is never more than say 10 PSI atmospheric pressure externally pushing on the system. In this application we can be pretty safe in assuming that if we can generate vacuum to this level we can generate pressure to this level.

I'm sure Diseasel300 will whip out his slide rule and Friden EC-132 calculator and make a fuss but we aren't trying to do something silly like send a human ( or 3 ) to the moon and back.