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
They weren’t programmed to the vehicle. A locksmith or anyone with a decent scan tool can program that.
The cases have little micro chips that’s talk to the car, if the cases have been replaced at some point you may have to take it to the dealer to get the key programmed, in addition I would make sure the key battery has power