On Board Diagnostic System
THE ON-BOARD DIAGNOSTIC SYSTEMAll 1990 vehicles will have an "expanded" On-Board Diagnostic System. The advantage of this system is shorter diagnosis time and more accurate decision making. This diagnostic test procedure has been designed using all the new features of the On-Board Diagnostic System to pinpoint the problem.
HOW THE ON-BOARD DIAGNOSTIC SYSTEM OPERATES
The Engine Controller monitors critical input and output circuits within the engine control, charging, and speed control systems, making sure they are operating correctly. Some circuits are tested continuously and others are checked only under certain conditions.
If the On-Board Diagnostic System senses that one of the circuit is malfunctioning for a predetermined amount of time during a check cycle, it will store a fault in memory. Each circuit monitored by the Engine Controller has its own fault message. The fault message will stay in memory as long as the circuit is malfunctioning. If the problem goes away after the fault is stored, the Engine Controller will erase the fault message from memory after 50 engine starts.