Mercury mariner 2009 Owner's Manual page 444

Locks and Security
5. Turn the ignition from the 1 (off) position to the 3 (on) position. Keep
the ignition in the 3 (on) position for at least three seconds, but no more
than 10 seconds.
6. Turn the ignition to the 1 (off) position and remove the second
previously programmed coded key from the ignition.
7. Within 20 seconds of turning the ignition to the 1 (off) position and
removing the previously programmed coded key, insert the new
unprogrammed key (new key/valet key) into the ignition.
8. Turn the ignition from the 1 (off) position to the 3 (on) position. Keep
the ignition in the 3 (on) position for at least six seconds.
9. Remove the newly programmed coded key from the ignition.
If the key has been successfully programmed it will start the vehicle's
engine and will operate the remote entry system (if the new key is an
Integrated Keyhead Transmitter). The theft indicator light will illuminate
for three seconds and then go out to indicate successful programming.
If the key was not successfully programmed, it will not start your
vehicle's engine and/or will not operate the remote entry features. The
theft indicator light may flash on and off. Wait 20 seconds and you may
repeat Steps 1 through 8. If failure repeats, bring your vehicle to your
authorized dealer to have the new key(s) programmed.
To program additional new unprogrammed key(s), wait 20 seconds and
then repeat this procedure from Step 1.
100
2009 Mariner (mrn)
Owners Guide, 1st Printing
USA (fus)