Smog test

When the engine control unit (ECU) memory is cleared, it takes a little driving before the ECU understands and determines that the various systems are ready or not. Insufficient running time or condition are reasons why the system is not ready.

Drive in city traffic for five or ten minutes, continue with highway driving condition for another five or ten minutes and then back to city driving for another five minutes. Stop for a few minutes and repeat the above process and you should be ready, unless trouble codes crops up.

Try resetting the ECM before carrying out the driving cycle.

First thing I would do would be to get the vehicle on a good scan tool and check for any codes. There are many that do not turn on the check engine light BUT can be in the computers and prevent the convertor test from running regardless of how many drive cycles you run.
If you want to try it without scanning, simply disconnect the negative battery cable for 5 minutes when the car and engine are cold. Reconnect it and go for a drive.

Start with between 1/4 and 3/4 tank of gas. Get on the road and accelerate to 50-55 MPH, drive for at least 5 minutes without braking, decelerate to 30 MPH, then accelerate again to 50-55 MPH, and drive for at least 5 minutes again without braking. If you hit the brakes for ANY reason you have to start over.
Now check the monitors.