I have an '18 and went from flashing constantly "turn before the key on and off several times", to 1 long blink on, followed by 2 short blinks on, and then out for about 5 seconds, then it starts over.
check to see if your horn is working or your cruise control as well if you have that option...if they are both not working...could be your clock-spring assembly in the steering wheel is broken....will need to be replaced.
Happened once on my '98. Here's what I did, and also some information I saved a while back. what worked on my '98 Frontier:
Open the driver’s door.
Pull driver seat belt completely out of its tensioner, allow for it to retract
Note the rubber covered button located low on the B pillar, a button which is pressed by the door when the door is closed. This is the Driver’s Door Switch (DDS).
Turn the ignition from OFF to ON.
Press the DDS at least 5 times within 7 seconds after turning the ignition switch ON.
Turn the ignition OFF.
Close the driver’s door.
Start the engine.
If you have the airbag light, it will show steady for a few seconds (the manual says 7 secs) after you turn the key from off to on (but not start) and then start to flash. Here is how to reset it:
1. Turn the key from off to on.
2. Watch the airbag light closely. It will stay on for a few secs. and then as soon as it blinks off (the start of the flashing), turn the key off instantly.
"Turn the truck to accessory and wait till the airbag light starts to blink. As soon as it does turn the key off and count to five. Turn it back on to accessory and wait till it starts to blink and turn it back off. You either do this 3 or five times (Im pretty sure its five). After you turn it off the fifth time count to five and turn it back to acc. The light should blink longer and slower. You can watch this as long as you would like. Finally turn the truck off and count to five again. When you turn it back on it shouldn't be blinking anymore. Hope that works but like I said, im going off of memory"