I asked the same question a few months back, and the best guess is that the sensor wasn't added till about MY 1990, even on Calif version M103s. The FSM is very confusing on the subject, because it indicates that the sensor was added as a production change some time in 1986, but this is contradicted by everything I've been able to determine.

http://www.peachparts.com/shopforum/showthread.php?t=244987

__________________
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