How OBDII WorksAll modern cars have an on board computer system that keeps it in check and highlights problems to the driver. This computer system constantly receives information from sensors in the engine and adjusts the system settings so the car can run smoothly. When a problem is detected the computer cannot fix itself so it triggers a warning to the driver. The technician can use the OBDII equipment to more accurately identify a potential problem area and resolve the engine fault. The system also produces a code that can be used to help identify the area and nature of the problem.With the right equipment running a car diagnostic is a straightforward process as many cars have an On Board Diagnostics computer interface. This interface allows for a technician to use one tool to identify problems on virtually all makes and models of cars. The computer scanner is inserted into the interface connector and once the car's model, vehicle identification number (VIN) and engine type is entered into the scanner the identify and diagnostic code can be accessed. It is this code that helps the technician to know where to look to find the problem.Not all ELM lights on will cause a running problem and may remain on for years without undue concern, if for example there is poor starting , excessive fuel consumption , poor running or idle conditions then perhaps its time to plug in a OBD device and see what is going on. When they say industry standard communication that doesn’t mean all cars and all systems, often specific vehicle manufacturers diagnostics will be needed to run certain tests, many manufacturers have these systems such as….•Peugeot have the Peugeot planet •Citroen have the Lexia interface •Volvo have the Vida system•Vauxhall use OPcom •VW group use VAG com •Ford have IDS •Landrover use JLR Moongoose system •Toyota use GTS •Fiat use MultiECUScan •Jaguar use IDS or JLR•ETC ETC Most garages will have a generic diagnostics interface from suppliers such as Snap on Mac tool Autel, Bosch which are sold with subscription to garages which you can buy but the ongoing expense would be a unnecessary burden for most end users. So there is a large market for cheaper interfaces such as ELM327 which if Bluetooth enabled can be linked to your mobile phone they lack activations such as running pressure pumps or release VW electronic brakes, but will aid in fault finding. Ebay and google have listings for various system such as Autocom CDP , Delphi , Autel or Wurths WOW software only thing you will need with some of these devices is a basic laptop.So what does the scanner tell me about my problems here is an example of a diagnostics of a customers car view document what we can see is some anomalies, first thing to recognise is not all fault codes are important as some are stored in the memory unless they are deleted for eg low voltage across various system well if the battery has been flat at some point then the system will store this as a fault until its deleted, perhaps you have a problem and decide to start unplugging component with the ignition on these will flag as faults same goes for some other component ABS sensors. Best advice is take a note of everything that is throwing up a fault then simple delete all fault codes and rerun the system after an ignition off and restart or turn over engine, then see what reappears , this is were the relevant info comes in.