P0190 FORD -

Question

I have a 1998 Ford Escort @ 111,500 miles, 2.0 L motor. It works fine in the past. However, today, when I drive 4 persons (including me, about 520 LBs) and turn on the air conditioning, the "service engine soon" lights on. It is my first time to drive so many persons with the air conditioning on. So I scan the car with OBD 2 scanner and get the only code P0190 and show that the emission inspection fails. That is, the red led is on in my OBDII 3030, which means as follows:
RED LED - Indicates there is a problem in one or more of the
vehicle's systems. The red LED is also used to show that DTC(s)
are present. DTCs are shown on the Car Reader’s LCD display. In
this case, the Multifunction Indicator (“Check Engine”) lamp on the
vehicle's instrument panel will light steady on.

What should I do then? There is no such problem before. Actually, there is no code two months ago.
Thanks very much for your great help.