Driving Without the Fob

How much gas do you have in the tank? That's how far you can go.

It's a safety issue: No one wants their car stopping on the freeway just because the battery dies in the key fob.

Tom

 

I heard of an Infiniti owner putting his fob on top of the wipers to free his hands. He forgot it was there and drive off. Light came during drive but car drove fine. $500 mistake since fob fell off in 20 mile drive..,,

 

Plus it is designed to work even when the battery isn't in there. You should be able to start your car holding your fob close to the starter button. The point though, is not so much how much gas you have in the car, but when you need to start your car again...

 

I did this test with our first Prius (2007) because I was curious. My wife had the only key in her purse and she got out of the car to go shopping. I drove through to the gas station, got gas and came back to pick her up with no problems...I just made sure NOT to turn off the car while filling up (engine was off, so no fire danger).

So, to answer your question: You can drive as long as you like without the key FOB or a dead key FOB battery. Just don't shut off the car if you don't have the key FOB, or else you are stuck.

Bottom line. You need the key FOB to start the car. If the battery in the key FOB is dead, you have to pull out the emergency key in the FOB to open your door manually with the key. Then you have to hold the key FOB right next to the start button, as you push to start.

Hope this makes since.

 

What can one do to prevent "hijacking" of the Fob signal code? I've heard it is possible for theives to steal the code from your fob after you park, then they drive away in your keyless car.

 

I'm surprised the dealer didn't go over this w/you and the OP. My salesman specifically went over this w/me when I picked up my car and the scenario of switching cars w/someone. (On the Gen 2, there's a slot where you insert the key fob, which has been removed on Gen 3 and changed to holding it near the power button.)

 

Don't most systems now have rolling codes, so that the hijacker records a stale code that won't work again?

After temporarily removing the remote lock/alarm system in the household's '97 car due to intermittent false squawks, I chose to leave it out due to the easily spoofed non-rolling codes of that era.

 

Yes, the fobs use rolling codes. Because of this it takes more than an RF sniffer to steal your code and then steal your car.

There is a man-in-the-middle attack that will work, which involves a two local receivers and transmitters connected to two remote receivers and transmitters. The local unit talks to the car, transmits the data to the remote unit, which then talks to the fob. When the fob replies, the data is linked back to the local unit, which then relays the data to the car. The local unit must be in close proximity to the car, and the remote unit must be in close proximity to the fob.

While this method can be made to work, it isn't very practical. I wouldn't lose sleep over it.

Tom