2022 CX-5 Key fob question regarding car camping

[sm1ke]

I will do this later today. Thank you!

Hope the results are fruitful!

 

[Conrad 16.5]

How long were you away from the car during that time?




You tested this on your car? I'm about to test mine while I'm at work, just to satisfy my curiosity lol




That's an assumption on your part. My post assumes that @Ess925 is referencing the car's battery, not the keyfob, but it is written in a way that could apply to either the car battery or the keyfob battery. The portable battery booster recommendation was due to the car's battery drain concerns, but it's also just good sense to carry a portable battery booster in the car.

It could be the case, which is probably why the OP posed the question in the first place. "Smart" keyless systems work on a process of check and verify. The keyfob is always "on", sending out a weak signal. When the keyfob is close enough, the car interprets that signal (the check) and waits for a request from the keyfob to verify an action (engine start, unlock door, etc.). If there is no request made, the check times out, and the process repeats. This is what drains the car battery, if the car doesn't have a system in place to deactivate a keyfob in close proximity. Some new cars have this system in place, and some don't.

I'm not convinced that's the way Mazda's fobs work.

A few years ago, back when I was active on a Kawasaki MC forum (I left because of the idiotic brand of politics there at the time), we had this very same discussion about the MC fobs our bikes came with. We actually had a Kawasaki rep explain it to us.

The Kawasaki fob is always listening, not transmitting, but listening. It's listening for the signal from the bike that gets transmitted when the key is pressed down (same as when the button on the CX door handle gets pressed). When the Kawasaki fob 'hears' the signal it's listening for, it verifies the signal and if it's good, the fob then sends a signal back to the bike informing the bike that it's ok to start. A turn of the bikes key, after the verification, then allows the start button to be engaged and the bike starts up.

Why would Mazda's fobs send out a weak signal at all times? What does that signal do? From a design standpoint, that makes no sense.


Oh, and it seems that my assumption was correct, the OP was talking of the fob battery.

 

[Conrad 16.5]

@Ess925, if you want, you could test your use case right now.

Turn the car off and leave your keyfob in the cupholder, then lock all the doors. The car should beep a bunch of times to remind you that they keyfob is inside the car - ignore this and make sure all the doors are locked. Ensure your other keyfob is well out of range of the car.

Wait an hour or two inside the car, ensuring that you don't touch the keyfob at all. Now try to start the car without touching the keyfob. If the car doesn't respond, or you get a key error, pick up the key and drop it in the cup holder to "wake" it.

Try to start the car again. If the car starts, you have a keyfob that will sleep and not drain the battery if it's left in the car. If the car starts on the first push, before touching the key, don't leave your key in or near the vehicle because it doesn't have a “sleep” mode.

If you don't want to wait in the car, you can also do this test by leaving the driver's side window open all the way. Just make sure you can park it in a safe place (like a locked garage) and that you can reach the engine start button without opening the door. When you come back to the car later, press the engine start button. If the instrument cluster says "No key detected", you're good to go. But if it says "depress the brake and push the start button" or something like that, the keyfob doesn't go to sleep and you would need to use a Faraday box to block the signal.

The OP has to sit in the car for an hour or two? Ok then, good time for a nap, I guess?

Seems to me that I recall reading in the owner's manual something about the car possibly not detecting the fob if it's placed in the cupholder area. I could be wrong, but I'd bet money that I read this.

 

[RedBaron]

Interesting. I will get a spare made and give it a try. Thanks!

No need to get a spare to test it, just take out the 'skeleton' key from inside the fob and leave the main body of the fob in the car.

How long were you away from the car during that time?

All day... probably 8-10 hours.

Oh, and it seems that my assumption was correct, the OP was talking of the fob battery.

No, the opposite. OP said:

I was concerned that the "communication" between the fob and the vehicle would drain the vehicle's battery.

Mmmm, no, I didn't know that there is a way to start the vehicle if the fob's battery is dead. Wouldn't that mean that the car could also be started without the fob? Please explain to someone who isn't a car person (me)

If the fob battery is dead, you push the Start button with the end of the fob (it's in your manual). Then it's in close enough proximity that the car can 'energize' the chip and read it. And no, you cannot start the car without the fob.

 

[7eregrine]

Pretty sure key fobs don't sleep or wake. They are passive. You push the starter button and the car then looks for the fob. No fob, no start. As someone else said that would be a terrible design.

 

[sm1ke]

The OP has to sit in the car for an hour or two? Ok then, good time for a nap, I guess?

No, they don't have to sit in the car. I provided an alternative method at the end of the same post you quoted and bolded.

Why would Mazda's fobs send out a weak signal at all times? What does that signal do? From a design standpoint, that makes no sense.

Oh, and it seems that my assumption was correct, the OP was talking of the fob battery.

Sorry about that, I had read it from a reputable source and assumed it to be true, but looking more into how relay theft attacks work, I think I'm mistaken. The keyfob is not always "on".

On your other point:

Whoops, I see that I wasn't clear. I was concerned that the "communication" between the fob and the vehicle would drain the vehicle's battery.

 

[sm1ke]

After thinking about it more, I'm not convinced that doing the tests I had suggested earlier would answer the question of "will my car battery be drained if I leave the keyfob in the car".

The only way to be absolutely sure is to completely block the signal to and from the keyfob. Disregard my other previous suggestions.

 

[youri]

You tested this on your car? I'm about to test mine while I'm at work, just to satisfy my curiosity

It is in the manual for the advanced keyless system. I am not sure about the “non-advanced keyless system” though.

Key Suspend Function​

If a key is left in the vehicle, the functions of the key left in the vehicle are temporarily suspended to prevent theft of the vehicle.
To restore the functions, press the unlock button on the functions-suspended key in the vehicle

 

[markfm]

If you have any EZpass, the little gray plastic pouch that comes with them should work to block communication.

Alternatively, wrapping a fob in a piece of aluminum foil will block the RF.

 

[ctbale]

Whoops, I see that I wasn't clear. I was concerned that the "communication" between the fob and the vehicle would drain the vehicle's battery.
Mmmm, no, I didn't know that there is a way to start the vehicle if the fob's battery is dead. Wouldn't that mean that the car could also be started without the fob? Please explain to someone who isn't a car person (me)

Youtube

 

[Conrad 16.5]

Ess925 said:
I was concerned that the "communication" between the fob and the vehicle would drain the vehicle's battery.

Reading for comprehension. I should do it more often. My bad.

 

[Conrad 16.5]

Snip...
Mmmm, no, I didn't know that there is a way to start the vehicle if the fob's battery is dead. Wouldn't that mean that the car could also be started without the fob? Please explain to someone who isn't a car person (me)

The fob has two devices inside to ID itself to the car and allow it to start.

One is powered and requires a battery and can work over a small distance.

The other is akin to a RFID chip, and it requires no battery. This chip has to be placed in very close proximity to the Start switch. Inside of the area of the Start switch is an induction coil and when the fob is near the energized coil it enters the coils magnetic field and with its own small induction coil the fob picks up enough juice (it works in the same way that wireless charging works for your cellphone) to power the chip and the signal the car is looking for to start.

 

[Conrad 16.5]

Pretty sure key fobs don't sleep or wake. They are passive. You push the starter button and the car then looks for the fob. No fob, no start. As someone else said that would be a terrible design.

Only the newer, HUGE fobs have the sleep function.

 

[Ess925]

The fob has two devices inside to ID itself to the car and allow it to start.

One is powered and requires a battery and can work over a small distance.

The other is akin to a RFID chip, and it requires no battery. This chip has to be placed in very close proximity to the Start switch. Inside of the area of the Start switch is an induction coil and when the fob is near the energized coil it enters the coils magnetic field and with its own small induction coil the fob picks up enough juice (it works in the same way that wireless charging works for your cellphone) to power the chip and the signal the car is looking for to start.

Thank you!

 

[Ess925]

Thank you everybody! I ordered a Faraday bag and emailed my salesperson at the dealer to see if my fob has a sleep function. Either way, I should have it covered.

 

[Conrad 16.5]

Thank you everybody! I ordered a Faraday bag and emailed my salesperson at the dealer to see if my fob has a sleep function. Either way, I should have it covered.

Don't be surprised if your salesperson knows nothing about the fobs sleep function.