A few days ago (late in the evening and pouring with rain) the doors failed to open with the electronic key, after a few tries I used the mechanical key for entry and then immediately put the electronic key in the ignition to prevent triggering of the alarm. I drove off and the alarm repeatedly triggered every time I touched the brakes. Stopped removed and reinserted the key, still the same. Got out, tried again to electronicaly lock and open the doors but still nothing, the side indicator light would flash so I guess the wireless signal was getting there but nothing else. Had to abandon the car and walk home. Next morning after a few tries the darned thing started to work again, unlocked and locked every time. Only problem now is the alarm indicator lamp (centre console) is on continuously, previously it would start flashing to show alarm activation when the doors were locked, so I guess the alarm is now not working, I am also worried about a repeat with the electronic lock. Has the cars computer controle become confused ?, if so is there a reset or reset code?, or is it more likely to be a contact or sensor. Any advice would be appreciated.
Dave

I've had no more problems with locking/unlocking so maybe this was a one off glitch. The alarm seems to be working ok but the red led is still on continuously. ( This is the red light in the middle of the rocker switch which dissables the internal motion sensor and the anti towaway function.) Normally this would flash momentarily when changing a function or flash continuously when the alarm is armed and doors locked. I've been advised the alarm backup battery may be faulty but I dont know where it is.

Any advice would be appreciated even if you dont have the complete answer.

Dave.

I would worry more about the batteries in the key.

I also would advise trying the remote using the trunk and passenger side recievers if it happens again.

I would also point out that two separate security systems are involved with your events. The RCL remote control is radio frequency operated to lock and unlock the doors and to command the ATA (alarm system - separate from the locking system). The alarm is not released or set with the manual key. Neither is the alarm reset with the electronic key function at the electronic ignition switch EIS. There also is a separate security system DAS that is involved with the handshake the key does with the EIS. This handshake is not dependant on the battery operated part of the key. There is a signal that is sent from the EIS to a chip embedded in the key which then resonates a return signal (powered solely by the original signal) that makes the "hand shake". Once this happens the EIS releases the lock and empowers the engine management system.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

the key is powered by the signal sent to it from the EIS?

wow, I'd love to find out how that works, what kind of a chip is this?

where can I get some more info on this?

xp

I don't know the workings of the chip at the quantum level, but the concept is that the chip needs no power of its own, Look at the various wallet keys that have no batteries.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Steve,- Many thanks for the excellent explanation of the system, armed with the additional knowledge I tried today to re-create the original event but without success, everything works OK, it locks, it unlocks, the alarm works, the motion detector works, if I unlock with the mechanical key the alarm starts to wind up but as soon as I put the key in the ignition the alarm stands down which is all as it should be. Batteries in the key were replaced in February , even so at the time of the event I did blame them until the problem turned into the 'cant stop the alarm nightmare'! The odds of having more than one fault must be very high so I guess that whatever happened (the lock function and the alarm glitch) must be linked in some way even if the systems are seperate. Hopefully it wont re-occur, certainly it is impossible to diagnose when the fault is no longer there.

The only remaining symptom is the red led in the motion sensor/towaway switch which is now permanently lit, nothing in the owners information discribes any situation where this led is lit continuously so I guess something is wrong. I did try disconnecting the vehicle battery for 10 minutes in the hope of creating a re-set but no such luck. If this remains the only problem I can live without being able to switch off the motion sensor or towaway function .

Again thank you for your excellent system explanation,
Dave.



XP190, yes it is quite interesting, as I understand it the key is a sort of 'passive transponder or resonator' for the EIS security signal, a bit like the anti theft store tags used on expensive items to stop people shoplifting but more elaborate, I Guess Steve could give you a more technical explanation.
Dave.

I had have had several faults like these in 98 e-classes.
When the led in the alarm switch comes on constant, it is
a pretty good indication that the pse (pnuematic locking pump)
has an internal fault. In every case that I have worked on, it
has been water related. The PSE pump sits in a well under the
rear seat cusion right next to the battery. It is mounted in a foam
capsul that does a great job of absorbing water. On every car,
there was a leak from the sunroof tray, a doorseal, sunroof drain
tube, ect ect. the pse was usually flooded and the connectors
were full of water.
A starting point at least.
Good luck.
DR.D

Thanks DrDiesel, it's great to get advice from guys like yourself and Steve otherwise faults like this can be very confusing .
The red led light has now reverted to normal, so everything is now OK. The pump is dry and no water anywhere in the underseat compartment, HOWEVER 2 days before the original event I did clean the engine compartment with a pressure washer. I was very carefull to keep the jet away from anything sensitive or electrical but when you mentioned water I am now wondering about it. Does the vac system input air from anywhere up front? , or might there be some other link?
Dave.

No, pressure washing then engine should not have effected the
system. It was the "heavy rain" that got me thinking, but since you checked and there was no trace of moisture near the pump
That probably wasn't it either. May have just been an intermittant
internal electrical glitch with the pump. When the LED comes on solid, there is a fault in the electrical portion of the pump.
Only time will tell. If it happens again, have your MB retail agent
check for computer fault codes stored in the system.
I hope all is well from here on.
DR.D