It is possible to turn off the check engine light on a vehicle, including a Grand Am, by disconnecting the battery. It must remain disconnected for at least five minutes. In some cases, this won't remove the trouble codes, but it will turn the light off temporarily.
The check engine light can also be turned off by using a scan tool, commonly known as an OBD or OBDII, to check the codes and reset the light. The OBD tool is suitable for some older model vehicles that have a check engine light. The OBDII is only suitable for vehicles manufactured starting in 1996.