When trying to start my car with either of my spare keys, the engine turns over and then stops and the immobilizer system light starts blinking. The manual says this is a signal for a malfunction and to bring it to a dealership - I’d love to avoid that as the main key I use doesn’t have this issue.
What could be going on that 2/3 of my keys are failing to start the car?
There’s nothing wrong with your car.
The normal key has an RFID chip embedded inside, the valet key does not. (Or the other keys are not programmed to the vehicle.
FYI, If you lost the programmed keys, Honda has a backdoor to bypass the immobilizer via a VIN specific “brake code” to prevent having to tow to dealership.
https://static.nhtsa.gov/odi/tsbs/2016/SB-10087261-2280.pdf yeah