On Board Diagnostic Networks
The vehicles computers are networked together in most cases by a Can-bus network. Individual computers (Body Control, Engine, Transmission, ABS, etc), share information with each other, from their sensors via the Can-bus network. If they pick up a fault with one of their sensor or other computers they will log a fault code.
Scantools are used to communicate to the vehicles On Board Diagnostic Network (OBD). We plug a scantool into the diagnostic port and can read stored fault codes, live data and reset warning lights. Most manufacturers have there own proprietary software and a mandated OBD, OBD-II or EOBD software loaded. Our scantools can communicate with both proprietary and mandated software on most vehicles.
Each computer(ECU) logs fault codes. If they are bad enough then the computer will turn on a warning light in the instrument panel. After plugging in the scantool these codes can be read then cleared. The ECU will then reset the fault code when the fault next occurs. In the OBD-II standard onlone, there are over 15000 fault codes available for the manufacturers to use.
Most ECU's have live data available for access with a scantool. Live data are sensor readings provided by the ECU via the Can-bus network. Because this data comes from the ECU it can give an indication of what the ECU is seeing or doing at that point in time. Helpfull though it is, the data transfer rate is quite slow. For faster more accurate measurements we use digital storage oscilloscopes.
Scantools are also used to reset warning lights and service lights. Some parts will only work properly in the vehicle once they have been coded in. Parts like ECU's, keys, injectors and in some vehicles batteries. Coding allows electronically controlled parts to be recognised by other ECU's on the Can-bus network. Some parts like fuel injectors and batteries need to calibrated to work accurately with the control systems. These in many cases this is something that can only be done with a scantool.