300e Anti Theft Alarm
 

1990 300E 3.0

Recently I noticed that as soon as I try to open my car from driver side door, alarm goes off. But, this problem is not from passenger side door. Further, the alarm problem is intermittent.

Please advice how to check. Thanks

It is most likely your key lock!
 

I tried different things until I eventually had to replaced the whole key door lock from the dealership. Not cheap!

My dad had a similar problem with his 1995 E320 driver's door. The dealer replaced the door lock mechanism, but the source of the problem was a loose electrical connection under the front passenger carpet. Unsnap the carpet/sound insulation insert and remove it from the car so that you can inspect the electrical connections to the hidden black box that bolts to the floor. The oxygen sensor cable runs from the driveshaft tunnel toward the passenger door ... ignore that one.

Thanks. I will check it this weekend.