System Diagnosis
The self-diagnostic capabilities of this system, if properly utilized, can greatly simplify testing. The ECU has been programmed to monitor several different circuits of the engine control system. If a problem is sensed with a monitored circuit, a fault code is stored in the ECU.
The setting of a specific fault code is the result of a particular system failure, NOT the reason for that failure, such as failure of a specific component. The existence of a particular code denotes the probable area of the malfunction, not necessarily the failed component itself.