Hello all,

Just bought a 300SL (1990) and it's at my tech's shop for a few routine things. Yesterday, he locked the car and went to drive it 5 mins later. It won't start -- the green light on the drivers door doesn't flash (alarm staying armed). We only have the two "regular" keys, and the infrared keys didn't come with the car.

He has figured out that the drivers door handle was somewhat broken (some kind of plastic piece) and the previous owner had glued it together. It apparently broke and won't "disable" the alarm computer. Problem is, the alarm computer tells the engine computer to disable the engine so it won't crank (starter interlock).

Possible solutions according are:
-Disable the relay that provides the starter interlock. Apparently a relay (K38 I think) grounds the starter whenl it's ok for the car to start. I suggested pulling the relay and bridging the contacts to keep the starter grounded at all times. This was my suggestion but he didn't seem to like it (will it work??)
-Order a remote key. Tech says this will enable & disable the alarm properly even if the handle is screwed up. He says once we disable it, he can yank the plug on the alarm controller so this won't happen again. Is this actually going to work or will I just be out another $200 for a remote key? Will the key still operate the door locks remotely or will it be a throwaway item since the alarm box is disabled?
-any other ideas? We're both at wit's end. He's a former MB tech and says these are so theft-proof that once the engine computer has been shut down, only the alarm box can re-enable it.

We've tried to use the trunk or pass. door to disable the alarm but it doesn't work. Apparently the system needs all of the parts there (like ABS) or it doesn't work. I suggested disconnecting the drivers door handle but that didn't do anything since apparently the alarm "sensed" it wasn't there and wouldn't authorize an unlock signal from the other locations.

Any thoughts? Any help? We can't drive the car and the temporary plate runs out tomorrow (can't get any more temp plates) so we'll have to start towing the car to move it!

Wife is ready to kill me (this may have been obvious but thought I'd point it out..)

Neal
(neal@bhattmail.net)

__________________
'83 300SD 335,000km (207k) mi SOLD
'87 560SL 163,000km (101k mi) SOLD
'86 300SDL 356,000km (220k mi) SOLD
'92 500SEL 250,000km (155k mi) SOLD
'90 300SL 140,000km (87k mi) SOLD
'01 S430 260,000km (161k mi) SOLD
'03 SL500 167,000km (104k mi) SOLD
'07 S550 4MATIC 235,000km (146k mi) SOLD
'07 GL320 CDI 4MATIC 348,000km (215k mi)
'13 GL350 BlueTec 4MATIC 170,000km (105k mi)
'14 SL550 72,000km (43k mi)

Yuuck! What a mess! If you just got your car, do it right. Your mechanic is right, once the remote master key is synced and operating you can engage and disengage your alarm system, however the sensors are located in the door handle. Don't go grounding, or rigging anything up as you could goof it up. Have you removed the door handle from the car? I guess you have since you know it is broken. So first thing is to replace the door handle, When you remove it the Infared connectors come loose and it is very difficult to get them back in right when replacing it. Take a look at the video at the link below, that will help with removing the door handle, the key has to be in the lock. The major point is, the door handle is broken, it caused the fault, repair or replace it and it should recover the fault. If after replacement it doesn't remedy, then disconnect the battery and reconnect (neg side) to reset the controller. Better yet, disconnect the battery while doing the repair. Good luck.
http://www.mbca.org/northtexas/repair_videos.htm

PS it takes awhile to load.

__________________
Brian W. Heitman

www.MBCA.org/northtexas

Join MBCA!!!

Thanks Brian..

So if I order a remote from the dealer (I believe they are VIN-matched and come pre-coded), I should be able to unlock the car, disconnect the alarm box, then just use the regular key from then on?

Out of interest, why would the remote key work if the regular one doesn't? Since I can't "disable" the starter interlock by opening the pass door with the regular key, why would the remote work?

Just wondering before I go off to order a key...

Neal

__________________
'83 300SD 335,000km (207k) mi SOLD
'87 560SL 163,000km (101k mi) SOLD
'86 300SDL 356,000km (220k mi) SOLD
'92 500SEL 250,000km (155k mi) SOLD
'90 300SL 140,000km (87k mi) SOLD
'01 S430 260,000km (161k mi) SOLD
'03 SL500 167,000km (104k mi) SOLD
'07 S550 4MATIC 235,000km (146k mi) SOLD
'07 GL320 CDI 4MATIC 348,000km (215k mi)
'13 GL350 BlueTec 4MATIC 170,000km (105k mi)
'14 SL550 72,000km (43k mi)

Neal,
The remote key will operate your alarm system, however I would repair/replace the broken sensor in the door handle first. The remote infared key relates to this sensor as well on that vintage, as you stated they all have to be working together. This will fix your problem, then go and buy a remote key after you are up and going. The point is fix what is broken first, then you can get your remote key. How do you know the sensor in the handle is broken? Do you know anyone with a car like yours? What I do is I swap the part with a car that it is known working prior to purchasing so that I know that is the problem, since MB parts are so expensive. Just some ideas. Fix what is broken first before adding more variables to the problem. ha ha.
Brian

__________________
Brian W. Heitman

www.MBCA.org/northtexas

Join MBCA!!!

I've read this post and am unclear as to what locks or doesn't unlock and what status the three sets of lock indicators are reading. So I don't have enough information to offer my own opinion of a course of action, but I will offer a few points.

A 1990 SL is not supposed to have K38 or any other starter lock-out feature interlocked to the alarm system. That was not introduced until '93.

The horn should sound immediately upon opening a door or the trunk if the alarm is armed. Are you sure the alarm is not disarming? By the way, the indicator lamps next to the handles are controlled by the infrared controller and not the anti-theft alarm.

There is nothing in the door handle which arms/disarms the alarm when the key is used. This is done through microswitches on the lock mechanisms of the doors and trunk which are wired in parallel. If the alarm is armed, any one of these signals can disarm it.

The infrared remote control arms/disarms the alarm with a signal wired to the same input on the alarm controller as used by the microswitches. So, I don't suppose having a working infrared remote would be of any benefit to getting your car running.

well that is good news, that means that it isn't your alarm system causing your car not to start, however it looks as if you have a new problem. Thanks Bobterry.
Brian

__________________
Brian W. Heitman

www.MBCA.org/northtexas

Join MBCA!!!