Here are some common causes for this behavior:
* Loose or corroded connections: A loose or corroded connection in the wiring harness, particularly related to sensors, can cause intermittent failures. The connection might make contact sometimes and fail at others. This is especially common in older vehicles due to age and exposure to the elements.
* Faulty sensor: A sensor (like the oxygen sensor, mass airflow sensor, crankshaft position sensor, etc.) might be failing intermittently. It might work correctly most of the time but malfunction occasionally, triggering the CEL. This is a very likely cause given the age of the vehicle.
* Intermittent electrical issue: A short circuit, bad ground connection, or other electrical problem could be causing the intermittent fault. These can be tricky to diagnose.
* Low fuel pressure: A failing fuel pump or other fuel system component could cause intermittent issues resulting in the CEL.
* EGR valve problems: The exhaust gas recirculation (EGR) valve is prone to problems in older vehicles and could cause the light to come on intermittently.
To find the actual cause:
1. Read the diagnostic trouble codes (DTCs): You'll need a code reader (available relatively inexpensively at auto parts stores) to read the stored trouble codes from the PCM. These codes give clues to the specific problem.
2. Inspect wiring and connections: Carefully check all wiring harnesses, connectors, and grounds related to the components indicated by the DTCs (or if no code is available, to the common culprits listed above). Look for corrosion, loose connections, or damaged wires.
3. Test sensors: Based on the DTCs or suspected components, test the relevant sensors using a multimeter or a specific sensor test tool.
4. Consider professional diagnosis: If you're not comfortable performing these checks, take it to a mechanic who has experience with older vehicles. They'll have the tools and expertise to diagnose and repair the problem more efficiently.
Ignoring the CEL can lead to further damage, reduced fuel efficiency, poor performance, and even catastrophic engine failure. It's best to address the issue as soon as possible.
