XC40 won't start from the button, but will start from the app

[poleposition]

It is a strange fault that it can be started with the app, but not with the start button.

Hope you have warranty cover.

Please let us know how you get on.

[n16bs]

Yeah very strange. I half-expect a call on Tuesday saying "It starts fine, what's the problem?".

[eugen61]

Remote start from the app sends the engine start command directly to the car, bypassing the need for physical wireless key authentication. The key is still needed to drive away the car as a safety feature. This leads me to suspect that your issue might be related to the key not properly authenticating with the car. Please keep us updated on the outcome.

[STmichael]

Have you ever thought the car may not see the brake pedal has not been pressed. It does not sound like a key fob issue as the car opens and you would get a key not detected fault on the cockpit screen. Can you turn on the ignition by holding in the start button? Also if you press the brake pedal can you see the brake lights come on? Not sure if the ignition needs to be on for the brake lights to work or not. If they do not come on that would also point to the brake switch being at fault.

[n16bs]

This is a good call. I do not remember if the parking brake can be turned off with the engine off or not. But FWIW I was not able to turn it off after the issue started. Could be the same problem with the brake pedal sensor.

Will see what the dealership will say on Tuesday.

[n16bs]

Ok so the dealership called:

They were able to start the car after 1. Replacing the battery in the fob 2. Removing an AirTag that I had attached to the fob ring 3. Placing the fob on the armrest reader.
They say that the battery was borderline dead, and ofc they say that an AirTag should not be attached to the fob. This makes little sense to me as the batteries in both fobs were replaced around 5-6 months ago. The AirTags were attached since the beginning of my ownership and the fobs worked flawlessly. Previously when the battery was dying, the car warned about it and was still able to start using that fob. Now there were no warnings. So it seems the batteries in both our fobs died simultaneously without a warning, and the AirTags were preventing the armrest reader from seeing the fobs. And the car WAS playing the startup animation when the button+brake pedal are pressed, instead of just saying that the key is not present. So I have a mixed feeling about it, it is good that the car can start now, but I do not completely buy the battery+AirTag as the source of the issue.

Additionally, they said that the fuse for the lambda sensor is missing. This one is even weirder. I was checking the fuses yesterday, and I took a photo of the fuse box before that. Indeed, there is no fuse in that slot. It was the first time I opened the fusebox. The car was on scheduled maintenance at the dealership a month ago. Surely they should have noticed it missing then? How did it become missing in the first place?

Anyway, they will return it on Tuesday after doing more checks.

[eugen61]

I do not completely buy the battery+AirTag as the source of the issue.

A key fob with depleted battery has to be placed precisely on the marked sensor in the armrest for the handshake to take place and a ring attached AirTag might prevent that. I had a similar issue by not placing my depleted key on the proper spot. Also, Apple AirTag is NFC equipped and might interfere with a low battery key’s NFC sensor.


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[poleposition]

Yes, the handbook does warn about not having any other items near the backup reader when placing the key on it.

When you get the car back I would check that you can start the car with the backup reader with the key with no battery in it?

Also agree that the dealership saying that both keys had flat batteries is unlikely, but I would remove the airtag if trying to use the backup reader.

Hope they can find something else before they give you the car back.

[Rifleman]

I’ve had an Apple AirTag on the car key ring for the last 4 yrs, never caused a problem.

[poleposition]

I think the Apple Airtag is only likely to be an issue when you are trying to use the backup key reader, it won't affect normal use of the key?

As eugen61 explained above?