Mercury Grand Marquis 1998 Owner's Manual page 57

Controls and features
You can program up to three personal codes to unlock your vehicle. These
codes do not replace the permanent code that the dealership gave you.
Erasing personal code
To erase all of the personal entry codes programmed to a vehicle:
1. Enter the factory-set code.
2. Press 1/2 within 5 seconds of
step 1.
3. Press and hold 1/2 for two
seconds. All of the vehicle doors will
lock and then unlock to confirm erasure.
Unlocking the doors and releasing the trunk with the keyless entry
system
To unlock the driver door, enter either the factory-set code or personal
code (each digit pressed within 5 seconds of prior digit). The interior
lamps will illuminate.
To unlock all doors, enter the
factory-set code or personal code
(driver door unlocks) and press 3/4
within 5 seconds.
To release the trunk, enter the
factory-set code or personal code
(driver door unlocks) and press 5/6
within 5 seconds.
After the factory-set code or personal code has been entered, you can
unlock all doors (press 3/4) and release the trunk (press 5/6) as long as
the controls are pressed within 5 seconds of each other.
Locking doors with the keyless entry system
It is not necessary to enter the factory-set code prior to locking all doors.
To lock the doors:
1. Press 7/8 and 9/0 at the same
time.
56
1 2 3 4 5 6 7 8 9 0
1 2 3 4 5 6 7 8 9 0
1 2 3 4 5 6 7 8 9 0
3 4
1 2 5 6 7 8 9 0