My wife has a 2004 Pontiac Grand Am... v-6 and the check engine light stays on.. also the security light. We have changed the oil and filter and checked everything as far as the engine maintenance and everything seems fine. Why do these two lights stay on. We bough the car used from a dealership

Check for codes by attaching a code reader or scan tool to the Data Link Connector, located under the dash. Many auto parts stores will do this for free.

In regards to the security light, some newer GMs have a PassKey 3 system, which is a passive security system. It allows you to use the car but will sometimes shut it off. Check to make sure your key has "PK3" stamped near the head; if not, you need to have a coded key to match.

my wife has a 2004 Pontiac Grand Am... v-6 and the check engine light stays on.. also the security light. We have changed the oil and filter and checked everything as far as the engine maintenance and everything seems fine. Why do these two lights stay on. We bough the car used from a dealership
How long have you had the vehicle? Time and miles... the dealer may have a way to help you.

Have all the codes checked. Maintanance is great for the life expectancy of the car and can even make it run better.

But don't forget that the check engine light is motivated by excessive hydrocarbon emissions. That may be from the engine or the evaporative emissions system (EVAP).

The security light is another issue entirely. The ignition lock cylinder is likely worn and isn't allowing the PK3 module to properly read your ignition key, even though you may have been using that same key since you bought the car.

Have these both of these concerns diagnosed. Don't be surprised to hear that they are totally unrelated. Let us know what is found.