I successfully used this technique on my Acura MDX, and my understanding is that this works on most modern Acura/Honda's, so hopefully this works on the NSX factory keyless entry remote.
In my case, my wife lost one set of keys/remote for our 05 MDX, but I had a spare fob from an 04 MDX lying around. Although the part number was slightly different, it worked just fine, and I paired it with the valet key for now. Saved myself close to CAD $500 in key/remote and programming from the dealer.
NOTE: On the MDX it wasn't sufficient to switch the key to the off position, I had to physically remove the key when it says to turn ignition switch off.
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1. Turn the ignition switch on (II on the ignition)
2. W/in 1-4sec, push the transmitter lock or unlock button with the transmitter aimed at the keyless receiver unit. (Just at the steering wheel is fine)
3. W/in 1-4sec, turn the ignition switch off
4. W/in 1-4sec, turn the ignition switch on(II)
5. W/in 1-4, push the transmitter lock or unlock button w/ the transmitter aimed at the receiver again.
6. W/in 1-4sec, turn the ign. switch off
7. W/in 4sec, turn the ignition switch On(II)
8. w/in 1-4sec, push the transmitter lock or unlock again.
9. w/in 4 sec, turn the ign off
10. w/in 4 sec, turn the ign ON
11. W/in 1-4, push the transmitter again
12. Confirm you can hear the sound of the door actuators. W/in 1-4sec, push the trans lock or unlock button again.
13. W/in 10sec, aim the transmitters (up to three) whose codes you want to store at the receiver, and press the transmitter lock or unlock buttons. Confirm that you can hear the sound of the door lock actuators after each transmitter code is stored.
14. Turn the ignition switch off, and pull out the key.
15. Confirm proper operation with the new codes
In my case, my wife lost one set of keys/remote for our 05 MDX, but I had a spare fob from an 04 MDX lying around. Although the part number was slightly different, it worked just fine, and I paired it with the valet key for now. Saved myself close to CAD $500 in key/remote and programming from the dealer.
NOTE: On the MDX it wasn't sufficient to switch the key to the off position, I had to physically remove the key when it says to turn ignition switch off.
-----------------
1. Turn the ignition switch on (II on the ignition)
2. W/in 1-4sec, push the transmitter lock or unlock button with the transmitter aimed at the keyless receiver unit. (Just at the steering wheel is fine)
3. W/in 1-4sec, turn the ignition switch off
4. W/in 1-4sec, turn the ignition switch on(II)
5. W/in 1-4, push the transmitter lock or unlock button w/ the transmitter aimed at the receiver again.
6. W/in 1-4sec, turn the ign. switch off
7. W/in 4sec, turn the ignition switch On(II)
8. w/in 1-4sec, push the transmitter lock or unlock again.
9. w/in 4 sec, turn the ign off
10. w/in 4 sec, turn the ign ON
11. W/in 1-4, push the transmitter again
12. Confirm you can hear the sound of the door actuators. W/in 1-4sec, push the trans lock or unlock button again.
13. W/in 10sec, aim the transmitters (up to three) whose codes you want to store at the receiver, and press the transmitter lock or unlock buttons. Confirm that you can hear the sound of the door lock actuators after each transmitter code is stored.
14. Turn the ignition switch off, and pull out the key.
15. Confirm proper operation with the new codes