I am not a mechanic, but I have read up a bit on the drive cycle, when I was having problems with my wifes car after clearing OBD codes. I am sure someone else can elaborate on here more, but the way I understand it, certain things need to be accomplished. Driving in certain conditions, I do not know what exactly they are but it is a possibility that some of those conditions have not been met.
With a quick Google search I found this. Hope it helps...
Generic OBD II "Drive Cycle"
Most OBD II ("On-Board Diagnostics II") diagnostic monitors will run at some time during normal operation of the vehicle.
However, to satisy all of the different Trip enable criteria and run all of the OBD II diagnostic monitors, the vehicle must be driven under a variety of conditions. The following drive cycle will (theoretically) allow all monitors to run on (??) vehicle. (Note: Drive cycle specifics vary by vehicle!)
1. Ensure that the fuel tank is between 1/4 and 3/4 full.
2. Start cold (below 86°F /30°C) and warm up until engine coolant temperature is at least 160° F (typically requires at least one minute; up to 3 minutes).
3. Accelerate to 40-55 MPH at 25% throttle and maintain speed for five minutes.
4. Decelerate without using the brake (coast down) to 20 MPH or less, then stop the vehicle. Allow the engine to idle for 10 seconds, turn the key off, and wait one minute.
5. Restart and accelerate to 40-55 MPH at 25% throttle and maintain speed for two minutes.
6. Decelerate with using the brake [or the clutch!] by coasting down to 20 MPH or less, then stop the vehicle. Allow the engine to idle for 10 seconds, turn the key off, and wait one minute.