[fw840ix]

so my 2018 x2 stopped detecting one of my key fobs.



once i get in the car, it says no key detected and to place it on steering column. i do and the car starts. but once i exit the car, keyless access doesnt work and i need to go thru the same process yet again. battery has been replaced even though the old one was fully charged.



clearly the car recognizes the fob but for whatever reason it doesnt take... i need to do this every time i get in the car.



any suggestion on a remedy will be greatly appreciated!

[//TMT]

Did you replace the battery correctly? It's easy to mangle the contacts. You might have to ask the dealer if they can test it.

The steering column thing reads an RFID chip, which doesn't require battery power in the fob. There are actually several circuits/keys in there.

[rice_rocket88]

Definitely sounds like it's behaving as if your key doesn't have batteries. Last time I replaced ours the actual new 2 pack was bad! I put the first one in, no dice.. second one in, nothing. I then took it out of a working remote and it was ok. So this is when I opened my second pack and then the battery worked. Frustrating and seems impossible, but it's not the first time I've read in these forums.

[fw840ix]

it wasnt mangled before i replaced the battery i would assume... it's not like i messed with the innards that cause this problem. the fob had been stored in a drawer. so before i changed the battery it stopped working. i checked the battery with the voltmeter and it's fully juiced. i put in a fresh battery and the problem persists. i suppose the fog could have just gone dead but i mean how many moving parts n a fob? i would guess zero...

[//TMT]

The fob is a rather complex device, with capacitive buttons, a unique code with a cryptographic transmission protocol, a UHF radio, and an RFID chip. Oh, and don't forget the physical keyblade.

That last device (the RFID) is not powered directly, it emits a response when it comes in range of a requesting device's signal. Such as, the one inside the steering column. That's why the car actually starts once you enter.

The buttons can get "stuck" by physically coming into contact internally, this causes them to drain power at the same time they fail to register, because the circuit needs to see a break/make cycle. Sometimes, pressing all the keys repeatedly can clear this kind of issue, but more often it needs dismantling to clean the rubber click membrane, and the board surface below it.

You put the "+" side out, right? My key isn't marked at all as to orientation.

You can't test batteries properly without load. Putting a voltmeter on them will often read the rated value, but it can drop to zero when demand is drawn. Use a proper button-battery tester if unsure.

These are just some possibilities. It's pretty tough to diagnose, if it's not just a flaky battery.