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

[STmichael]

I’m not buying their explanation. If the battery in the fob was flat you would not have been able to open the door. Then trying to start the car you would of had a key not detected message. Also having a flat battery you would have still been able to start the car putting the fob on the detection area although there could be something in the AirTag/nfc argument.
I am also surprised that if the lambda sensor fuse was missing that you did not have an engine management light on the dash., although if you could not start the car you may not of had a chance to see this.

[eugen61]

If the battery in the fob was flat you would not have been able to open the door.

That’s a good point. When my fob went dead, I had to unlock the car through the app and start the engine the same way after failing to place the fob on the proper spot in the armrest. We don’t know if the OP used the key to unlock the car, were the doors even locked to begin with?

[Jaycee750]

None of us know more than the Volvo techs and the OP. Fact is that cars are too complicated now with too much electronic cr@p. Faults like this will happen to all brands because as we know computerised stuff crashes, malfunctions and has issues from time to time. It goes with the territory.

[percymon]

Wasn’t life so much easier when you turned a key in the door lock and the ignition barrel ?

We pay hundreds of pounds for this technology that’ ultimately is an inconvenience

[Jaycee750]

Wasn’t life so much easier when you turned a key in the door lock and the ignition barrel ?

We pay hundreds of pounds for this technology that’ ultimately is an inconvenience

Yep. Then all this stupid safety tech that often puts us in danger. I yearn for the old days.

[n16bs]

> We don’t know if the OP used the key to unlock the car, were the doors even locked to begin with?
Both our keys were unlocking the doors just fine.

Got the car back. Wasn't able to talk to the mechanic. The paperwork only talks about the missing fuse. Both fobs' batteries are at 3V, a new one I have at hand measures at 3.3V. So it looks like they haven't changed the batteries. 3V looks healthy tho? The fuse box now has a fuse for the lambda sensor.

So to test things I removed the battery from my key and placed the key on the reader under the arm rest. The car starts just fine. Then I put the AirTag on top of it. Still, it starts just fine. All in all, it seems the keys are just fine.

Now the fuse. I never opened the fuse box before. This means that the car was missing that fuse for at least a month, since the service appointment in December. Maybe longer. No visible problems with that and no lights on the dash whatsoever. So for me, the fuse does not explain the issue.

The only remaining explanation is that it had fixed itself overnight while sitting in the dealership parking lot. ¯\_(ツ)_/¯ Tomorrow I'll try to remove that fuse and start the car to see what will happen.

[poleposition]

All very strange, have you owned the car from new?

From looking at lambda sensors, it appears that the fuse might be for the sensor groups heating. Lack of heating will not stop them working, just takes longer to get up to temperature and give accurate readings. I assume the fuse missing does not bring up a warning light/message in the car, but does show up on the dealer's test equipment as a DTC code.

At least you have much more information if it happens again ...

[n16bs]

I have owned it since July, around 20000 km. Now at 102000.

[percymon]

I wonder if a previous owner took that fuse out to prevent a EML light on the dashboard. Due to failing lambda sensor