Will a flat keyfob battery prevent a car from starting?

[Diddums]

I feel like I should know this, but I'm doubting myself so here we are.

Sister in law's i10 occasionally fails to start. She's in Saffrica so hopping over to help out is a bit of a drive so I'm helping remotely (see what I did there?!).

She panics when it happens and she's a bit nuts so the question of "explain exactly what happens when you turn the key" is met with "dunno lol".

Anyway, she also mentions that the car doesn't always unlock when she presses the fob (which is 5 years old and still on the original battery) so the battery is obviously dying.

I'm assuming that the car has an immobilizer, the signal for which is transponded from the key. But will a dead battery prevent the signal getting to the car, leaving her stranded? For clarity she says if she leaves the car for 10 minutes it starts up just fine, which again supports my theory that the immobilizer locks out and needs a few minutes to reset before reading the key again.

Does this theory make sense? I'd have thought that the key has a passive chip but everything points towards the dead battery, so I need to rule that out.

 

[peterwalkley]

Tell her to buy a new battery, they're usually the little CR 2032 round jobbies used in cameras.

 

[cuke2u]

The car should have somewhere you can place the key, if the fob battery is dead, sometimes they are somewhere near where a conventional ignition switch might be.
I expect the car has a handy vehicle manual where you'd find this info

 

[Thekwango]

Keyless start I take it? In which case yup. There’ll be a push lock (can’t remember the proper name) slot somewhere, most likely hidden in a storage compartment which will power the fob in the event of a dead/dying battery.
But tell her to just get the battery changed and stop being such a diddumsette.

 

[Heisenberg]

No. The transponder chip inside the key doesn't rely on the battery in the fob. That's only for remote keyless entry. Of course the transponder could be playing up. Doesn't she have a spare she could try to rule that out?

 

[iamdjdz]

Definitely try the battery first, had this before in a Passat but it gave a warning saying key battery was low as well. Started fine near the ignition button but had to use the key pullout to unlock the car. YouTube is good for working out how to change your fob battery.

 

[Nasher]

On mine there is a key which pulls out of the key fob to open the doors and then you hold it up against the start button to start it.

 

[Diddums]

Thanks for the replies folks. It's not keyless, but I'm still quite suspicious of a dead battery. I've told her to use the spare key for a few weeks and see how it goes, I still reckon it's the dead battery in the key. As illogical as it might sound, my spidey senses are pointing in that direction. I'll report back in a week or two with the outcome

Thanks again, you absolute beauties <3

 

[Drumroll]

Replace the battery, but you have about 15 seconds to do it before the key loses its codes, and them it's a visit to the dealer to re-code the key at some expense.
I always do mine, but the safest bet, if she's not confident on doing it, go to a Timpson and they'll do it at a fraction of a dealer, safely.
Few cars now allows to stop the key from transmitting. Mine a double press to the locking button stops the key, useful specially for the spare, which I keep safe. Also stops the dirtybags from amplifying it's signal and unlocking the car.

 

[Nasher]

Replace the battery, but you have about 15 seconds to do it before the key loses its codes, and them it's a visit to the dealer to re-code the key at some expense.

That's only applies to keyless ones afaik.

 

[BananaDunka]

That's only applies to keyless ones afaik.

The paired rolling codes could de-sync if the key has no battery for too long. Easy to re-sync once inside the car and battery is replaced. Different makers have different pairing instructions. Just google the one for any specific car model. You can actually use any remote fob for the same model and re-sync it to your car so the doors lock/unlock. You'd need to be in the car first to do this of course.

A dead battery on a normal turnkey fob has no relation to the rfid chip that talks to the immobiliser when the key is in the ignition barrel.

 

[Mart2912]

A dead battery on a normal turnkey fob has no relation to the rfid chip that talks to the immobiliser when the key is in the ignition barrel.

Yeah, was going to say the same thing. Recently got new casing for my Golf key and the RFID chip is not connected in anyway.

 

[Nasher]

Passive RFID chips are powered by the device scanning them. Active ones (which broadcast) need a battery.