Hello,
This may be of some help to somebody. My '96 E300 is my daily driver. For the past couple of days, my car would not start due to the immobilizer being activated (red and green alternating lights in rearview mirror with key in position 2). I tried everything I could find on the internet with no success. I replaced the K40 relay several years ago, but went ahead and ordered another one. Since the part won't arrive for a week, I started trying different things. What finally ended up working was I turned the key into position 2 and while the lights in the rearview mirror were continuously flashing, I removed the 15 amp fuse at position f6 on the K40 relay. The lights stopped flashing. I turned the key into the start position and it started! It ran fine, but put out the code P380. I shut the car off and re-inserted the fuse. I turned the key and there were no red and green lights. The car started and I cleared the code. So far, everything is working normally. Hopefully this can help keep someone from getting stranded with this issue. Keep a phillips head screwdriver in the car to access the K40. Thanks

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1996 E300D

Thanks for the info. I have a '97 E300. Haven't experienced this, yet, but it's good to know this "work around" will get me back on the road.
Gotta be over 100 degrees F. "down there" this time of year? Lived in Fayetteville for about 10 years and can vouch for the fact there are TONS of rust free vintage autos, of all makes and models down in Dixie, with nothing more than a little "red Georgia clay" on the undercarriage! Appreciate the "heads up" and thanks for sharing!

This happened to me last year while out and about in the '96. I was able to clear it by cycling the locks using the real key inserted into the driver's door. I locked the doors and then unlocked them, and was then able to start the car. Might not work in every case, but could be a good thing to try before following the procedure outlined by brightem.

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- Greg -
1973 220D, The Prodigal Benz
1974 240D

Thanks for posting your solutions, good things to know to try if this comes up!