Looking for simplest ELM327 command to test if ECU is on

We are developing an ELM327-based device and need to send a command just to test whether the car's ECU is on or not.

For all other vehicles I've tested with, simply sending the command "0100" (to query the supported PIDs for Mode 1) is sufficient. If the ECU is ON, it will return a valid response. Otherwise, I'll get "UNABLE TO CONNECT".

However, for the Leaf, the only way I've been able to talk to the ECU is to send a series of init commands (such as turning headers and CAN formatting off, and then specifying a specific CAN address).

Does anyone know if there is a "generic" command that will work on the Leaf, but also work on other cars?

Once I've determined the ECU is ON, I can jump through extra hoops - but the basic detection needs to be as simple as possible.

Any thoughts or ideas would be appreciated.

Thanks.

I would guess you could just put the ELM into monitor mode with a mask set to allow all or some common subset of messages through. If the CAN is alive you will get flooded with messages and overrunning the ELM buffer. If the CAN is idle you will get nothing.