These large units are compatible with all cars and contain software that analyzes the signals received from the car, displays a text or diagrammed readout of any malfunctions found and suggests possible solutions to the problems. Smaller units for the home or small shop technician can provide a variety of levels of data, some approaching the sophistication of the big shop consoles. However, they are usually limited to one OBD-II system type, unless adapters can be purchased. Scanning OBD-II signals can also provide valuable information on the condition of a used car purchase. It shows three different types of signals.
Occasional flashes show momentary malfunctions.
It stays on if the problem is of a more serious nature, affecting the emissions output or safety of the vehicle. A constantly flashing MIL is a sign of a major problem which can cause serious damage if the engine is not stopped immediately. Hard failure signals caused by serious problems will cause the MIL to stay on any time the car is running until the problem is repaired and the MIL reset. Intermittent failures cause the MIL to light momentarily and they often go out before the problem is located. The freeze frame of the car's condition captured in the computer at the time of the malfunction can be very valuable in diagnosing these intermittent problems.