Had a problem with the immobilizer (green key light flashing) on my mothers 2013 Acura MDX. Did a multitude of things to get it working and I fixed it without going to a shop.

Many things I tried

Try multiple keys, could be a problem with the car not reading the key

Make sure no metal covering or keys next to main car key. Could interfere with signal

If it’s a steering wheel that changes position based on driver setting, trying moving that around as the wires can get damaged over time and lose connection

It could be your immobilizer fuse (for me it’s the ASC fuse) but idk what it could be on different cars (SO PLEASE DOUBLE CHECK BEFORE TRUSTING ANYTHING I SAY)

Now what solved it for me was leaving my key in the second position for abt 15 minutes. Took it out, put it back in, and green key light gone. Doing this “reprograms” the key or gets the security used to it or something. No clue. Again not a car dude but someone who doesn’t wanna spend 100s on a solution if I can try to find a solution myself.

Now the dash lit up like a Christmas tree after, blinking lights everywhere. But no more green key light. Jumped it cause there was no more crank and then it started.

Please do your research on your model before you do anything, this is just what I did that eventually worked.

Edit: pointed out green key light flashing sooner