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500SL 93, 600SEL 92, 380SEL 82, 200 84, 500SEL 82, 280S 76, 190E 92, 230 72, 300E 91, S320 01
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64 Posts
Discussion Starter #1
I have a 1994 C36. It has 75000 km.

It won't unlock. The indicator lights flash and it goes beep-beep and nothing happens. After I open the drivers door manually, it won't crank.
All lights come on in the dash, the A/c starts blowing, the windows/seats/lights/stereo all work. When I turn the key to start it, the lights don't dim.

If pull out the battery terminal an replace it (immediately) the car starts and works as if nothing happened - but the doors still don't unlock.

They do lock however, both with the remote in the key, and with the switch in the dash. They lock automatically when I put the car in D. Normally when I switch off the car, all doors unlock but now nothing happens. even when I unlock the drivers door or the boot manually, the rest of the car does not unlock.

The starting is disabled somehow when the door locks. i.e. if I start the car after disconnecting/reconnecting the battery and don't drive it (the driver door is still unlocked), then if I turn it off and start it again, it starts. But the moment I drive it, it locks automatically. Then when I stop, I can't start again. Even while it is on, if I use the button on the key, then it won't unlock. However, it sometimes unlocks using the switch on the dash.

It has a switchblade key with 3 buttons - lock/unlock and alarm. I have 2 keys - both seem to be working ok. There are no red/green lights on this car anywhere. The driver door has a keyhole and nothing else. The rear view mirror is the old type. So is the instrument panel - clock is set manually. The battery is new and everything is bright.

When I try to unlock, I can hear a small sound from the back (vacuum pump?). This seems to be ok because the car unlocks with the dash switch sometimes.

The only repair to the car in the past few days has been a change of coils/ignition cables/plugs and an oil/filter change. A month ago the dealer replaced the old K40 relay. But the car worked fine till 2 days ago.

It seems to have a mind of its own. The problem happened once a week ago but went away on its own after the car was parked overnight. Then it was fine till 2 days ago. Tonight I have left the battery disconnected to see if there is any change after a prolonged disconnection (few hours).

Please help someone - just completely in the dark about this. I read up the forums about CANs, keys, immobilizers and all such but just don't have a clue anymore.
 

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'01-E320 & 02-ST2
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31,631 Posts
These cars are very finicky about voltage. I would start by having the battery fully tested to ensure it is 100%. Then I'd check all the grounding points for the car.

Good luck.
 
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