I'm getting this as an engine code and also some intermittent hesitation with my '02 SE. I almost always have the SES light on because of the P0440 code which is something about the EVAP or Emissions, but I bought an Innova 3100 OBD II scanner and it is now showing the P0120 code consistently, which is the Mass Air Low Output code. I just changed the sensor in July and changed the air filter yesterday and reset the codes and it came right back again. Looking for anyone that might have some ideas. Thanks.

I think P0120 is a throttle position sensor error, not a mass air low output code.

P0120 = Throttle/Pedal Position Sensor/Switch A Circuit Malfunction.

P040 Info is here.