FOB doesn’t work but CA works?

[KuriousJorge]

Hi guys,

I’m a new E90 M3 owner and have been enjoying it lots for the past month. I came across a weird issue during my current road trip. The key fob appears to be dead. The car does not respond to any of the key presses BUT comfort access on the same key works just fine(door/boot lock/unlock and car starting with CA)! Could this be a battery issue? Should be quick to check by swapping a battery but unfortunately I’m still on the road now.

Thanks for your help!

[deansbimmer]

Yes. Needs new battery. Comfort access functions will always work if the battery is dead in the fob since the car's antennas will always sense the fob's transponder chip, but the fob doesn't have the power to transmit commands to the car.

[jdamore]

Originally Posted by deansbimmer

Yes. Needs new battery. Comfort access functions will always work if the battery is dead in the fob since the car's antennas will always sense the fob's transponder chip, but the fob doesn't have the power to transmit commands to the car.

Let me get this straight.. if you removed the battery from the fob, CA will still work? Car will start?

[deansbimmer]

Admittedly my post was confusing. You must insert the key in the dash to start a CA car with a missing fob battery. It won't unlock the car until the battery is replaced.

[jdamore]

Originally Posted by deansbimmer

Admittedly my post was confusing. You must insert the key in the dash to start a CA car with a missing fob battery. It won't unlock the car until the battery is replaced.

Right on, thanks for clearing that up!

In OPs case, the doors/boot are still locking/unlocking by CA (if I'm reading that right). As a new owner, possible the spare key is in the car?

[Scrippy]

Originally Posted by deansbimmer

Admittedly my post was confusing. You must insert the key in the dash to start a CA car with a missing fob battery. It won't unlock the car until the battery is replaced.

Yes. The door handle is very similar to a proximity card reader. It emits an inductive reactance field that is altered by the the chip in the fob (just like a proximity card) and that's it. The battery is solely for RF transmissions.