1998 Jeep Cherokee

The Engine Computer is constantly monitoring engine and other sensors. When it detects a problem, it sets a diagnostic trouble code in its memory. If the problem could adversely affect tail pipe emissions, it turns on the Check Engine light. Some relatively minor problems will allow the light to turn off while youre driving or after cycling the ignition switch off and back on.

Your mechanic, and some auto parts stores, will connect a hand-held computer, called a scanner, to read those fault codes. The codes will lead them to the circuit or system with the problem, not necessarily the specific part.

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