This is the fault message associated with code 9 of the check engine light in my car ('95 E420). I reset the light and waited till it came back on. It shows code 9 again so I know it is not just a fluke. I am wondering how to go about fixing this problem. I would think that I should first make sure that it is completely connected, and if the light still comes back on, replace it. From what I understand it is like a $12 part. Where exactly is the sensor located? What does it look like? Some assistance would be greatly appreciated.

It's on the driver's side headlight assembly housing in the engine compartment. It's either come loose or its bad.

Thank you so much. I feel like an idiot but at least I fixed it for free. I had replaced a headlight bulb last week and it must have come loose or I unplugged it to get the housing out of the way. It was completely unplugged and just hanging there.