I'm trying to confirm a fault on an electronic unit of which no documentation is available, I can't even tell which MCU it is so it's largely guesswork so far. It's an automotive control unit and let me describe the circuit as I understand it.
I have a simple switched ground input from the car which runs a control unit. It can be assumed the input pin on the MCU has a pull up. During the normal operation of car, the switch is normally open until the switch is pressed. Now the vehicle fault doesn't recognize when the switch is opened anymore, therefore I can assume the MCU input is connected to ground or thereabouts. (Short circuit?)
The unit has since been removed, and is not powered. When the resistance is checked between the ground rail and input pin - it measures 25 ohms resistance, which would be a low input.
My question is this: Does the 25 ohm resistance indicate anything? Is it typical for a rested state input pin?
Or can I conclude that it has shorted internally providing there is no physical short circuit on the PCB?