* Loose or disconnected gas cap: This is the most common reason for a check engine light, and it's surprisingly easy for a mechanic to accidentally loosen or not fully tighten the gas cap during other work. The system detects a leak in the evaporative emission system (EVAP).
* Sensor interference: While rare, it's possible something was bumped or disturbed near a sensor during the oil change. For example, a technician might have accidentally knocked a wire or connector near the mass airflow sensor (MAF) or another crucial sensor.
* Pre-existing problem: The issue might have already been present, but the light only triggered after the car was restarted after the oil change. The light might have come on due to a larger, unrelated problem.
* Incorrect oil type: While less likely to immediately trigger a light, using the wrong type or viscosity of oil *could* eventually cause problems and trigger the light. This is more likely to manifest as a longer-term issue, though.
* Forgotten to reset the service indicator light: Some vehicles will trigger a check engine light if the service reminder light isn't manually reset after an oil change (this usually isn't the case, but depends on the specific vehicle).
* Faulty diagnostic trouble code (DTC): In rare instances, there might be a fault within the car's OBD-II system itself, leading to a false positive.
What to do:
1. Check the gas cap: Make sure it's tightly secured. Sometimes just tightening it will reset the light; sometimes you might need to drive for a bit for the system to recognize it's fixed.
2. Get the code read: Visit an auto parts store (many offer free code reading) or a mechanic to have the diagnostic trouble code (DTC) read. This code will give you a much clearer idea of the problem.
3. Return to the shop: If the problem occurred immediately after the oil change, take the vehicle back to the shop that performed the service. They should diagnose and rectify any issue caused by their work.
Don't ignore the check engine light. Driving with a problem can lead to further damage.
