Air Mass Flow Sensor
 

I got a BBK cold air kit and my question is What causes the air mass flow sensor to through the check engine light on? could it be that the sensor is dirty, or does a dirty air filter cause this? The check engine light has been on since the day i installed my o/r h pipe. i got mil eliminators but the light never came off and now im starting to wounder if its been the air mass flow sensor this whole time.

A dirty MAF, strange air-flow patterns (like those from fenderwell CAI), etc can cause problems.

the types with a sharp turn just before the MAF cause the air stream to bias toward one side of the MAF which can throw the readings off. Other causes of CEL's are from over-oiling the K&N type gauze filters and good old fashioned grime buildup on the sensor.

To get your CEL off, first you should probably figure out exactly what code it's throwing. Once we know how it's freaking out we can tell you how to approach fixing it.