Engine light came on while my wife was stuck in traffic

The Engine Computer detected a problem, set a diagnostic fault code, and since the problem could adversely affect emissions, it turned the Check Engine light on to tell you. The place to start is by having the fault codes read. It's important to understand that those codes never say to replace parts or that they're bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. Many auto parts stores will read the codes for you for free.

Until those codes are read, don't disconnect the battery or let it run dead. That will erase the codes, then that valuable information will be lost.