We believe your Ford Taurus has emission monitor(s) which are not ready or completed yet. This is more than likely due to the problem which was triggering the check engine light to turn on. Since you've fixed the check engine light problem, the vehicle will now need to undergo a drive cycle in order to make the monitors (also known as readiness flags) ready. Emission monitors are internal self-tests which the ECU (engine control unit) performs in order to ensure all emission systems are functioning properly. When a problem which causes the CEL to illuminate is presented, the emission monitor pertaining to the emission system presenting a fault is unset.
It is recommended to drive at least 200 miles over the course of a week in order to hit all the specific sections of a complete Ford Taurus Drive Cycle. You may also follow the Ford Taurus Drive Cycle indicated below in order to complete the drive cycle sooner, however take extra caution when performing the drive cycle on city streets and highways as there are many stops, slow downs, and speed ups. Usually driving in normal traffic on both city streets and highways, over the course of a week completes the drive cycle. Just make sure at no time in-between driving the check engine light illuminates again... or else you'll need to re-diagnose the fault causing the CEL to illuminate. Perform this drive cycle at your own risk.
How To Complete a Ford Taurus Drive Cycle
The following procedure is directly from Ford and designed to complete the OBDII monitors required to get your Ford Taurus to pass the OBDII Monitors portion of the smog check, also known of the I/M readiness test. You may use a scan tool in order to monitor the status of the emission monitors as your Ford Taurus is being driven.
Drive Cycle Recommendations:
1.Your Ford Taurus's emission monitors (readiness flags) will complete quicker when using a "steady foot" driving style during cruise or acceleration modes. Operating the gas pedal in a "smooth" manner will minimize the time required for monitor completion.
2. Your Taurus' fuel tank level should be between 1/2 and 3/4 fill during the drive cycle in order to allow the EVAP monitor to run.
3. The Evaporative Monitor can only operate during the first 30 minutes of engine operation. During the EVAP portion of the drive cycle, drive in a smooth fashion to minimize "fuel slosh".
Drive Cycle Start:
1. If using a scan tool, go ahead and connect it now. Turn key on with the engine off. Cycle key off, then on. Select the appropriate vehicle make and model on your scan tool. Start your Ford Taurus WITHOUT returning to Key Off. Idle the vehicle for 15 seconds, and then drive at 40 MPH until engine coolant temperature is at least 170°F, which is normal engine operating temperature. 10 to 15 minutes of drive will achieve this.
2. HEGO Monitor - Cruise at 40 MPH for up to 4 minutes.
3. EVAP Monitor - Cruise at 45 to 65 MPH for 10 minutes (avoid sharp turns and hills).
4. Catalyst Monitor - Next, drive your Ford Taurus in stop and go traffic conditions. Include five different constant cruise speeds, ranging from 25 to 45 MPH over a 10 minute period.
5. EGR Monitor - From a stop, accelerate to 45 MPH at 1/2 to 3/4 throttle. Repeat this pattern 3 times.
6. SEC AIR/CCM (Engine) - Bring your Ford Taurus to a stop. Idle with transmission in drive (neutral for M/T) for 2 minutes.
7. CCM (Trans) - If your Ford has a manual transmission, go ahead and accelerate from 0 to 50 MPH, continue to step 8. For Automatic Transmissions, start from a stop and in overdrive, then moderately accelerate to 50 MPH and cruise for at least 15 seconds. Stop the vehicle and repeat without overdrive to 40 MPH cruising for at least 30 seconds. While at 40 MPH, activate overdrive and accelerate to 50 MPH and cruise for at least 15 seconds. Stop for at least 20 seconds and repeat step 7 five times.
8. Misfire & Fuel Monitors - From a stop, accelerate to 65 MPH. Decelerate at closed throttle until 40 MPH (do not apply brakes). Repeat this 3 times.
9. Readiness Check - If using a scan tool, go ahead and access the ON-Board System Readiness (OBDII monitor status) function on the scan tool. Determine whether all emission monitors have completed.
10. EVAP Monitor "Bypass" - Park vehicle for a minimum of 8 hours. Repeat steps 1 through 9.
