PeachParts Mercedes-Benz Forum - View Single Post

jay_bob · #4 09-12-2014, 05:55 PM

Switch in the air in its normal orientation - continuity, light on.
Switch in the air upside down - no continuity, light off.

These do fail pretty regularly and are not that expensive (~$25). Hella is the OEM manufacturer. I would just get a new one.

Note to all who follow who have a W210: They did a really interesting trick (?) with the coolant and washer tank sensors. Both sensors are wired in series to one analog input point on the front SAM module. There are series and shunt resistors inside each switch. The SAM reads the resistance of the chain of switches and resistors and can determine the various states of the system (i.e. normal, low coolant, low washer, or both). If one of the sensors has failed internally or is disconnected, the resistance value will be wrong and it will show "Display Defective" on the screen. The upshot of this point is that you cannot test a W210 sensor with a meter unless you know what the resistance values (both full and empty) are for a good switch.