The temp sensor is located on the top of the engine block on the left side of the valve cover, all the way at the back of the engine. There's a large black electrical connector plugged onto it, and its wire runs over to the left inner fender and ends in a 4-pin connector plugged into the ignition control unit there. The sensor is tested with an ohmmeter at various engine temperatures, and the results compared against a resistance-to-temperature chart printed in any good service manual. To perform these tests, you need a multimeter, available for about $25 at Sears, and a good service manual to walk you through the test procedures and give you the resistance specs for the relevant electrical component you intend to test. As already mentioned, the tests themselves are quite easy and quick to perform, anybody can do them. Of course, the alternative is to simply replace the sensor and see if that corrects the symptoms.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't