1998 Mbz E 320 - Whenever it rains you get an oil sensor defective message on the dash screen Could it be that a short occurs at the harness because of water leaks causing a short?

I have a 1999 E430 and I get idiot lights coming on randomly, too. I got one a while back that said the rear tail lights were out after I washed the car. I waited a while and it hasn't come back on since. There were no lights of any kind out. The oil sensor defective light came on today while we were travelling through Arkansas. It was a clear day -- no rain anywhere. I will tell you one thing that might have something to do with it. In my case, I found that you can check the oil level using the computer if you: turn your ignition key to the second ON position. This is the position that causes all of the dash warning lights to come on so you can see if any of the bulbs are burned out. Leave it in this position -- do not start the car. After about 5-10 seconds, it asks if you want to check the oil level. Push the "0" (zero) button on the dash twice. I did this while the engine was still warm twice and the computer said that the engine was overfilled with oil. Apparently you need to wait like 6 minutes before testing. I did not wait. I suspect what happened is the computer "sensed" that the engine was overfilled with oil a certain number of times because I didn't wait for the hot oil to get back into the pan before testing. Then other times the sensor told the computer everything was cool and the computer "decided" that the oil sensor is defective. I haven't gotten that one again, but I've learned not to leave the key in the second ON position (prior to starting the car) for more than a second or two unless the car has been sitting for at least six minutes. Otherwise that damn oil sensor light comes on again. Could your situation have something to do with the rain itself? I don't know, but I also wonder if you don't operate the car slightly differently when it's raining. Maybe you fiddle with the wiper blades or the A/C longer while the key is in the second ON position and this is just long enough for it to test the oil sensor and "conclude" that it's defective. These Mercedes are very finicky and I must admit that it is unusual driving a car that gives messages that may or may not be valid. On the other hand, it has never left me stranded and it purrs like a kitt.en when driving thousands and thousands of miles. Hope this helps.