Yeah its the sensor which is located on the front bumper right near the license plate. 1 screw holds it in. The whole thing is $50. On my 95 E320 it was reading +136F all the time or nothing at all. Rather than spend $50 and re-route an entire harness, I found a 1983 300 SEL at a local junkyard, cut the sensor off the front, cut my sensor off, and spliced the two wires together with the new sensor. I have had no problems since. I got the new (old) sensor free because the yard guys didn't think it would work. The big old Benz it came off from had a minor fire and the car had 315k miles on it. Of course, my 1995 had 39k on it at the time, but needed a new one!

Good Luck

__________________
________________________
2002 Mercedes-Benz E320 4Matic
1995 Mercedes-Benz E320 Wagon
2005 Land Rover LR3 V8 SE
1999 Audi A8 4.2L quattro