Without Scan Tool

The SMEC or SBEC monitors critical input and output circuits of the engine control system and charging system, and speed control system making sure they are operating correctly. Some are checked continuously and some are only checked under certain conditions.
If the on-board diagnostic system senses that one of the critical circuits is bad during a predetermined amount of time during the monitoring cycle, it will consider this a real problem and put a fault code into memory. Each input and output circuit monitored by the on-board diagnostic system has its own fault code. The fault code will stay in memory as long as the circuit continues to be bad. However, if the problem does not happen again after the fault code is put into memory, the SMEC or SBEC is programmed to clear the memory after 50 to 100 engine starts.