Regardless of whether it is powered or not, the crank position sensor only generates a signal when the engine is running above 25 rpm (above the cranking speed):


Here is what they look like from the inside:


Photo courtesy of Jerry Scott

The part numbers from ETKA A10Q Illustration 906-10 are:

G4 (Item 14): 034 905 381 igntion timing sender (black)
G28 (Item 15): 034 905 381A engine speed sensor (grey)



The G4 and G28 are both common across the Audi 80, 100, 200, UrS, RS2 range from 1985 MC to the 1997 UrS AAN and 1995 RS2 ADU and everything in between, i.e. good ones might be availble in wrecking yards.

You will get a code on the engine speed sensor as failed if you retrieve the codes with the engine off, i.e. false positive.

These can fail but it is not common. More likely to be the cam position sensor or fuel pump problems before these if you have a starting/running issue. You can change them yourself (easier than the knock sensors to get at). That said, they are magnetics and there have been cases of the sensors picking up metallic debris that causes them to malfunction. Therefore, you *might* want to remove and clean them if you are having strange starting or running issues. Here is an example of an engine speed sensor that had accumulated metal debris (the tip is magnetic):



The other thing that you *might* want to check when you are having strange starting issues is the presence of the timing pin (actually an elaborately shaped, square-ish bit) is still on the flywheel, as shown at the 8 o'clock position in the photo below (should be visible through the hole where the crank position sensor is located when the sensor is removed) (LINK to DETAILED G4 PIN INFO):


HTH