Vehicle computer diagnosing can be very intimidating.Technicians today certainly need a strong grasp on how electricity flows and acts. Weather you are testing an engine, transmission, body or any other control module they all use similar electrical principals to operate. There are 3 main things a computer needs to do its job. First thing it needs is Power. Usually 12 volts DC in a car or truck (but manufactures are researching 48 volts and higher because the electrical demands on cars keeps growing). Secondground and Third, input signals from various sensors throughout the vehicle. If any one of these main supplies or inputs are not correct, then the control module cannot perform its job.
Power and groundallows the modules to turn on in addition to supplying power and ground to the systems they control.Furthermore, they need good input signals from sensors in the different systems. In the case of an engine control module. Camshaft and Crankshaft position sensors as well as Oxygen sensors give the computer processor the proper data, so it can adjust the ignition timing, fuel control and variable valve timing to achieve the best power and fuel economy.
Recently we had a Chevy truck in the shop, I can already see you Ford and Dodge guys smiling. This truck had an intermittent rough running condition. When we scanned the engine computer we found several codes but the one that stood out the most was a Crankshaft position correlation code. This means the computer did not like the signal it got from the crankshaft position sensor. Control modules are programmed to know what a good signal is. Our tech monitored the sensor within the scanner and would see the signal was erratic. It would spike higher than normal and randomly go away. Once he tested the sensor and verified it was sending a proper signal out he turned to the computer. He disconnected the engine computer main connectors and found corrosion. This corrosion was not allowing a clean signal into the control module. Hence the module did not have good enough data to do its job. There is a saying I have heard many times in relation to computers. “Garbage in, Garbage out”. We cleaned the corrosion from the connector and the pins in the module, added some dielectric grease to help seal out any future moisture and now the truck is running great.