Hello I'm new to the forum, and was wondering why jumping the controll circuit on let's say an a/c system would fry the computer. I don't understand why you could jump a ICM signal but not a signal in the above circuit.
Welcome to the forum! I'm trying to understand your question so help me out here. You talk about the control circuit of an A/C system and frying the computer? And an ICM (Ignition Control Module). Do you have a specific sytem, video, bookpage... in mind?
Thank you, the video is chapter 2 identifying input circuits. In the video scannerdanner mentions that sending a signal (on GM GFI or ford TFI) trough the ICM wire that usually it sending a 5v square wave to the PCM with a test light to fire the injectors diagnosing a bad ICM (ignition control mod. ) , is completely safe. In not disagreeing with this, I don't understand why it is safe to " jump" this circuit but not others.
What you have to be really careful about is computer outputs, they are only designed to switch a specified current if you jumper a computer controlled relay (for example a fan relay or fuel pump relay) across the wrong terminnals theexcessive curent through computer will burn the driver.
Most computer inputs are designed to be fairly tough, for example a wheel speed sensor or brake pad wear sensor have to work in a very hostile environment and so the computer input is designed to survive water ingress and shorts.
Themperature sensor inputs have a high ressistance so it is virtually impossible to damage them certainly not by shorting to 5v reference voltage.
VR sensor inputs are very tough because VR sensors can generated fairly high voltages at high RPM.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
