I thought you could do a push in the gas pedal X amount of times and it will flash you a code on the dash. then look that up on the Net.. thus giving you the diag.
It works that way on the E30s. and E34s.
Google it..


Or if that is what you have already done thus the coolant temp, then try shorting the wires and seeing it the warning goes out. of so its the switch and check a U pull. Or I am sure any local shop can order one.