fuel trim malfunction

I have a 98 gst and i was driving the other day and my check engine light came on. I ran it on a comp and it said it was a fuel trim malfunction. What could cause this to happen?

It means the ECU is maxed out on one end of its range. It can make adjustments plus or minus some percentage. 29% in 2g IIRC, and 1g is similar. If the injectors are stock, and the airflow sensor hasnt been tampered with, its usually caused by an O2 sensor that is on its way out. If its not new, I'd replace that first. If the scan tool used to read the code can also read trims (any obd2 scantool or datalogger) check it out. I am wiling to bet long term fuel trim is plus 12%. There are other cuases but they are quite rare, unless I am forgetting something.