The multimeter you have is the same as mine and steve is right it measures duty cycle backwards. the red connector in 2 and black in 3 should give you the right numbers. I would expect your duty cycle to be around 20 to 30 this way. Depending on your car and X11 jack 'key on engine off' should give you 70%, if you get thirty either your coolant temp sensor is dead or your poles are switched. The chances of the coolant temp sensor being bad are negligible. So switch the poles then use that as your duty cycle. I based this on my car a 91 560sel. The manual should give you this info and I think it is fairly similar for most benz's. 190's I believe will give a different EHA reading though.
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)