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What fault code is stored?
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The check engine light comes on when the car's engine management system senses a fault, and this sets a fault code.
There are dozens and dozens and dozens of reasons for this light to come on.
The only way to determine why this light is on is to have the fault memory read from the car using a compatible scan tool. Once the fault memory is read, the failed component can be identified and replaced, and the light switched off using the scan tool. Many parts stores will do this for free, so check with those near you. If you cannot find a local parts store that scans faults for free, then you will need to pay to have the memory read out at a shop with the proper equipment.
If the light went out for 2 days and then came back, it is most likely still the lean code and the air filter was not in fact the problem. you likely have an intake air leak or a failed mass airflow sensor.
I hope that is helpful, please let me know if you have further questions, or if I can clarify anything for you.
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