Key not working.
 

I have a 2008 S40 and one of my keys just stopped working i replaced the battery on it and still not sign of it working. Though the spare works just fine. any ideas whats wrong with it?

I have the exact same problem. Key stopped working but works in the ignition (none of the buttons work on the FOB). And the spare key works fine. Replaced both batteries, the spare works like a champ and the key that stopped working still doesnt work. The batteries are installed correctly. How do you marry up the key fob buttons back to the car? Obviously the key is programmed to the car because it still starts it. Whats the magic trick to make it work?

When I replaced the battery, it took a few minutes before the re-rejuvenated key fob to transmit correctly. Have you tried again?

Your key fob has THREE locking functions. 1) Mechanical blade key: opens driver door and glove compartment only, will set off siren if used (???). 2) RFID chip in key fob shank: the REAL ignition key; does not need battery power, just proximity to sensor in ignition switch. 3) Key fob remote buttons: provide all normal door unlocking and remote lighting functions. Only this last function is powered by the battery.

I haven't tried again other than multiple hours the first day and haven't touched it since, just reliant on the spare key that is perfect! Will try when I get home... More to come

Nope still don't work. The slide out key works for the door lock, the key in the ignition works, so both of those are good it's the unlock, lock, trunk, lights, and immobilizer that doesn't work....even with the new battery in it. And the battery is installed correctly. Now how do you link that part back to the car.....?

You may need the help of DiCE / VIDA. You can get a copy of VIDA for free, and a Chinese clone of the hardware side from OEMscan on AliExpress. Your dealer, of course, can also do a scan, and in fact, if it is determined that a software download is the next option, is the only source.

There are a number of diagnostic trouble codes that seem to describe this: KVM-0001, KVM-0004, KVM-0005, KVM-0110, KVM-0115, KVM-E001, KVM-E010. One of the write-up is as follows, according to VIDA:

366: KVM-0004 Remote control receiver. No communication
Print

Diagnostic trouble code (DTC) information

Condition
For any type of key communication to occur, i.e. unlocking, locking, passive start or activating and deactivating the key, the keyless vehicle module (KVM) carries out a communication check using remote keyless entry (RKE). The diagnostic trouble code (DTC) is stored if the control module registers that the signal is incorrect.
The diagnostic trouble code (DTC) can always be diagnosed when the car is supplied with power.

Substitute value
None.
Possible source
Short-circuit to supply voltage in the signal cable
Short-circuit to ground in the signal cable.

Fault symptom[s]
Cannot be controlled with the remote control.

Wait: I just realized that only ONE key fob has failed. That argues pretty convincingly that your car's receivers are unchanged.

I would open up both the known good and the known bad key fobs and look closely for any differences. The circuit board you can see is the remote transmitter (the RFID chip (that is still working) is in epoxy in the "key" section of the fob).

If you replace that key fob, you will need to download revised software. Key fob (new, on internet) $80, dealer reprogramming $180 or so.

Is the car keyless? If not, there's a bulletin about this issue for 200 and 2009. It needs a new remote.

Resurrecting an old thread here. I have the exact same problem as the OP. Locked my car with the remote, went into the post office, came out and nothing on the remote works. The spare does work. Changed the batteries, the remote does nothing but it will still start the car without issue. HELP!

There isn't much you can do. Replace the battery. If that doesn't fix it then odds are you need a new key remote. Since the car starts then the ECM "sees" the part of the key that is programmed to the ECM. However, no other functions work. My guess (and it's just a guess) is you need a new key which means having it programmed to your car's computer.

I bought a car with one key and had to purchase a brand new OEM Volvo key that comes with all the necessary information for your dealer to program the key. They did this for about $75 plus tax. Used ebay keys do not have the required information and we do not have the required subscription from Volvo to use a DiCE tool with VIDA.

I'm hoping you find a better solution but I've never heard of one so far.

Volvo s40
 

Pls where can I get a new battery for my volvo S40 remote

Are you talking about the fob or the car? not sure what year your car is, but if you pop open the fob you should see either a 2016 or a 2032 or perhaps a CR2450. Next you can go down to Walmart and pick up a replacement. How to vids are all over Youtube.

CEM update required by Volvo
 

After facing the same issues as everyone on this thread and spending countless hours searching forums to find the answer, I believe this is the only fix. A bit of background first, my main key buttons stopped working and didn’t think much of it as I had a spare, however after a couple of years, that too also stopped working and it become a bit of a challenge locking and unlocking doors. I reached out to Volvo who quoted me a considerable amount of money for a new key as it would need to come from Sweden. Fast forward a few months later, the key finally arrives and I go into Volvo all excited that I’ll finally have a working key, but no, I get a call from them saying that the key works on the ignition but the buttons on the brand new key still don’t work, I explain that I cannot pay for a key that doesn’t work and they respond by telling me that it does in the ignition, after an hour of debating, the master technician arrives and tells me that they will do a CEM update on the vehicle but cannot guarantee this will fix the problem, however I would need to pay for it regardless, I reluctantly agree and they proceed with the update, low and behold, 45 mins later, I’m told the good news and the bad news.

Bad news is the new key buttons still don’t work but starts the vehicle.

Good news is both your old keys are now working fine with no issues.

in the end they decided to send the new key back to Volvo as faulty and only charged for the CEM update which was £45.

Please do let me know if this fixes your problem as it would help a lot of people spending weeks and months searching for the answer.

Remote, spare not working
 

Used spare key early am. Returned 2 car-would not work. Remote key would not work. Remote buttons did not work on doors. Tried hatch lock w/remote. Bingo ! Returned 2 driver's side. Pushed remote. Then inserted remote key. Key would not turn but ALL locks popped open !! Now, remote works, intermittently. Fingers crossed.