* Evaporative Emission System (EVAP) Issues: Problems with the gas cap, fuel tank pressure sensor, or other parts of the EVAP system are frequently the culprits. A loose or faulty gas cap is the *easiest* and cheapest fix to check first.
* Oxygen Sensor (O2 Sensor) Malfunction: Oxygen sensors monitor the exhaust and help the engine run efficiently. Failing O2 sensors are a common cause of check engine lights across many car models, including the 2004 Pacifica.
* Mass Airflow Sensor (MAF) Problems: The MAF sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can lead to a misfire and trigger the light.
* Ignition System Issues: Problems with spark plugs, ignition coils, or the ignition control module can also cause a check engine light.
Important Note: Simply knowing the light is on doesn't tell you the *specific* problem. You *must* use an OBD-II code reader to retrieve the Diagnostic Trouble Codes (DTCs) stored by the car's computer. These codes provide a much more precise indication of the underlying issue. Ignoring the light or guessing at the repair could lead to more significant and expensive problems down the line.
