Do you know how the 200 SLK R171 pressure monitoring system works?
I found this quote on another forum, Basically, your car will not have active TPMS (sensors in the wheels), but *may* have passive TPMS, activated by differential rolling radius of the wheels.
How does "differential rolling radius of the wheels" work?
They use the rotational sensors, that are part of the anti-lock brake system, to compare the rotational speed of each wheel. If there is a difference above a certain level (I am not sure what that is is RPMs) the system will tell you to check your tire pressure.