Part 3. OBDII "Readiness Flags" Test: Your 1996 and newer car, truck, van, SUV, or motorhome will not pass the smog test if certain "readiness flags" are not set. Some "check engine" related failures don't illuminate the check engine light, but do cause smog check failures. These faults are referred to as "readiness flag" faults. Readiness flags indicate that certain emissions systems which the OBD II computer has been monitoring have passed internal self monitoring tests, indicating that those systems are working properly. If the smog machine detects that there are certain readiness flags which have not set, the data will be relayed to the smog machine and your vehicle will fail the smog test.
In order to set all the proper Readiness Flags the OBDII system must complete at least one good drive cycle (in some cases two or three). A good drive cycle is a sequence of passing internal tests which the OBDII computer runs while your vehicle is being driven. This ensures all emissions systems are functioning properly. A drive cycle usually requires one to two weeks of ordinary everyday driving.
Readiness flag failures are often seen on vehicles which have had recent repairs requiring disconnecting of the battery, and/or the emissions computer. Disconnection of power to the ECU resets all readiness flags. These vehicles will need to be driven in order to reset the required flags.
