V50 General : How keyfobs work.

[elsmandino]

Hello, I have just read SwissXC90's really interesting explanation of how Volvo keyfobs work:

The process of adding a key requires that ALL keys be present

The process will enable only those keys physically present, and also disable all keys not physically present.
Thus ensuring all lost / missing / stolen keys not present on the day cannot be used to start the engine.

Part of the robust security concept.

And remember the way the keys work:

A passive (non-powered) transponder with a unique serial number is fitted to each key-fob. The serial number of the transponder is entered into the vehicle's immobiliser system, thus only known transponders can mobilise the vehicle (permit engine start).

An active (powered by the little battery inside the key) rolling code transmitted is used for the lock/unlock functions. The rolling code needs to be synchronised with the car's UEM to permit that remote control to lock / unlock car (and whatever other functions exist as buttons on the key).

A physical key blade is mechanically paired to the physical key lock in the driver's door, ignition switch and sometimes glove-box. A replacement means cutting a new key. Key blades cannot be disabled electronically. Only physical replacement of the locks can stop a stolen key blade from physically opening the driver's door.

When I bought my V50, a couple of years ago, I was given two keys: Key A and Key B.

Both keys could fire up the car on but only Key A could ever unlock/lock the central locking.

My dealer asked me to drive to my nearest Volvo garage as they claimed that Key B somehow needed to be "synced" back to the car - something I though was a bit odd at the time.

After waiting for an hour, I was told that the fob could not be synced and that they would have to be given a new replacement fob.

I was told to come back a week later and after another hour wait, I got the car back with a brand new fob - Key C.

The garage also gave me back the broken Key B as a spare, as it could still be used to use the car in an emergency, despite setting of the alarm first.

In light of the explanation above, am I correct in thinking that it is simply the active rolling code in Key B that broke and therefore the garage were never going to be able to fix it in the first place?

[eric19371]

I bought a '04 V50 yesterday that has exactly the same issue. Key A works fine, key B will start the car but the key fob won't unlock the car even with a new battery.

I also noticed that if I pressed the buttons on key B (which seemed to do nothing), and then pressed the buttons on key A they wouldn't work for about 20 seconds afterwards.

I am going to call a local locksmith to create key C as soon as I have time.

[SwissXC90]

Sounds like Key B has a remote control faulty transmitter. Or a flat battery. Or bad battery contacts There are companies that repair them.

If the key still starts the car then the immobiliser chip is still recognised.