rossc:
DVDdoug i work in automotive repairs which in these days is getting closer and closer to electronics. ive high end multimeters , texa, picoscope etc. sometimes amps is a must to find a drain on circuit. but how do the ecu's flag up a diagnostic short/open circuit if its either 0v/off or 5v/on? it has to be amps/ohms?
i thought it must have been amps. if its not amps can i measure ohms on an output pin?
Usually ecu use specific component for switching, called "smart high side switch", eg. BTS432E2 . This kind of component includes overcurrent protection, high temp. shut down and open circuit detection. A fault is reported by a status pin, an open collector output. Some of them can even output a (not so much accurate) current measurament .
Ciao, Ale.