This info I'm going to paste comes strait from the service manual:
Low Tire Warning (LTW) System
The Low Tire Warning (LTW) system detects differences in inflation pressures in one or more tires. The system uses the ABS wheel speed sensors to monitor the rolling radius of the wheel and tire assemblies. If a difference in rolling radius is detected, the ABS module illuminates the LTW lamp located in the instrument cluster. The LTW system must be reset when tire replacement, maintenance, system repair is performed or any time tire pressure is adjusted. To reset the system, press and hold the "Tire Reset" switch for a minimum of three seconds. The LTW warning lamp will flash 3 times indicating a reset has been initiated.
If the lamp illuminates always reset the tire pressure to specification before resetting the system. If the problem persists go to the symptom chart.
The LTW system is not capable of detecting rapid loss of inflation. The system may not detect loss of inflation in more than one tire.
The LTW system can be deactivated. For additional information regarding deactivation, refer to Section 418-01.
Tire and Wheel Runout
Excessive radial and lateral runout of a wheel and tire assembly can cause roughness, vibration, wheel tramp, tire wear, and steering wheel tremor.
Before checking runout, and to avoid false readings caused by temporary flat spots in the tires, check runout only after the vehicle has been driven far enough to warm the tires. For additional information, refer to Section 100-04.
Resetting procedures aren't an exact science (have you ever reset a change oil light on a Ford? You would think they are all the same, but they aren't) Since the instructions say hold the button down for "at least" 3 seconds, to me it means hold the button down until you see the low tire pressure warning light flash.
I hope that was helpful,