What model and year are we talking about here? Not sure what your coolant leak is all about, but if you have reason to suspect the CPS, the test is very easy and quick to perform. Even better, if the CPS (L5 sensor) proves to be bad, the repair is easy and inexpensive.

For my W124 with M103 motor, this is the main diagnostic test for that L5 sensor (see FSM section 15-1250 for complete description). Engine cold. Ignition off. Multimeter set to Ohms. Unplug the L5 sensor at the EZL. Positive probe on inside of pin. Negative probe on outer part of pin. Spec is 680 -1200 Ohms. If no, rplc L5 sensor. Your test may be different depending on year/model.

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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