From other threads on the 156 forum that there have been problems with pcmcia cards not delivering enough voltage to operate properly, try
http://forum.alfa156.net/forum/ and search for diagnostics.
As for me, I have an interface built, full version of alfadiag, but couldn't read the sensors, but now managed to blow the capacitor as thought it was the wrong way round, so de-soldered it and oh bugger it was the right way round. So now need to source a new one and try again! Bit of a steep learning curve here on diagnostics!