P38A What causes a keyfob to stop working?

300bhp/ton · Dec 1, 2022

Went away for a few days, thankfully took both keys. Night 2 parked up at the hotel and locked the RR. In the morning the keyfob would no longer unlock or lock the vehicle.

Fob lights up and the battery is fairly new (as in I'm 110% sure it isn't the fob battery).

Any ideas on what could cause this to happen?

pwood999 · Dec 1, 2022

RF Interference ?

300bhp/ton · Dec 1, 2022

pwood999 said:
RF Interference ?

Doubtful as the other fob seems fine. This was in Somerset, now back in Bucks and it still isn't working. Not 100% sure how to resync it, I think in the past the only way I've managed it is by entering the EKA with the key that isn't working. Sadly the electronic switches in the door latch are faulty and entering the EKA with the key is extremely difficult.

Colthebrummie · Dec 1, 2022

Have you tried swapping the fob batteries? I had a rover 45 that, for reasons unknown would kill fob batteries within a couple of weeks. I used to keep a couple of new spare batteries in the car cos it would happen without warning.

Col

Ratae · Dec 1, 2022

If the other fob is working fine it suggests a fob issue.
Don't assume the batteries in the non working one aren't the cause.

DanClarke · Dec 1, 2022

When mine does this I usually find that connecting my nanocom and doing a "clear RF memory" gets both fobs working again.
It is as if one keyfob gets out of synch with the rolling codes range or summat like that. Obviously there's one key I use all the time and the other doesn't get used.

Datatek · Dec 1, 2022

FOB has lost sync.

300bhp/ton · Dec 1, 2022

Datatek said:
FOB has lost sync.

Pretty much. Was curios as to the cause. Will try what Dan mentioned above.

Datatek · Dec 1, 2022

300bhp/ton said:
Pretty much. Was curios as to the cause. Will try what Dan mentioned above.

Unused FOB's do go out of sync as the rolling code moves on too far. Key in lock, turn to lock hold and and press the lock button, turn to unlock hold and and press the unlock button, that should resync the FOB. You may need to start with unlock.

Rubberknees · Dec 1, 2022

Always try to use my spare fob 2X's a week to keep in sink

300bhp/ton · Dec 2, 2022

Rubberknees said:
Always try to use my spare fob 2X's a week to keep in sink

Thanks. But that wasn't the issue.

Got the spare key out as we were going away. I then actually swapped the spare key to be the primary one as it has a new case. Worked fine the day before we went, was also fine 1st day away. Must have locked and unlocked the car at least half a dozen times, if not more. Worked fine the next day. It was then overnight it must have decided to stop working..... as it then wouldn't work the following morning.

easy-shaft · Dec 2, 2022

You mentioned poor microswitch on door lock. Another thread suggested this was my issue.
Before the last round of trouble, I got inconsistent results if the door handles were not fully home.

Lastly, when mine lost its sync, it refused to reset using it in the door lock and pressing buttons, until I first started the car with it and pressed buttons with key in ignition and engine running. Could have been a random event (for me)

kermit_rr · Dec 2, 2022

Mine sometimes doesn't work, but the light flashes on the fob.
The battery holder on the rear is slightly loose, if i press on it while pushing a button, it works

Datatek · Dec 2, 2022

easy-shaft said:
You mentioned poor microswitch on door lock. Another thread suggested this was my issue.
Before the last round of trouble, I got inconsistent results if the door handles were not fully home.

Lastly, when mine lost its sync, it refused to reset using it in the door lock and pressing buttons, until I first started the car with it and pressed buttons with key in ignition and engine running. Could have been a random event (for me)

If you car is post about 99, it has auto sync of the FOB when the key is placed in the ignition.

kermit_rr · Dec 2, 2022

Datatek said:
If you car is post about 99, it has auto sync of the FOB when the key is placed in the ignition.

if all the bits work

Datatek · Dec 3, 2022

kermit_rr said:
if all the bits work

True and assuming EKA and immobiliser functions are not turned off in the BECM

300bhp/ton · Dec 4, 2022

Datatek said:
If you car is post about 99, it has auto sync of the FOB when the key is placed in the ignition.

Mine is a 99 on a T plate. It is technically an HSE, but was built to Vogue SE spec by Land Rover SVO (I have a letter from them somewhere). It has 4 wheel traction control and a the Thor injection system. I've never got any of the keys to sync via this method.

Datatek · Dec 5, 2022

300bhp/ton said:
Mine is a 99 on a T plate. It is technically an HSE, but was built to Vogue SE spec by Land Rover SVO (I have a letter from them somewhere). It has 4 wheel traction control and a the Thor injection system. I've never got any of the keys to sync via this method.

Is the aerial for the FOB receiver disconnected, does the FOB LED flash when the key is inserted in the ignition? If the LED does not flash, either the transponder coil in the ignition barrel has failed or perhaps the EKA and/or the immobiliser have been turned off in the BECM.

300bhp/ton · Dec 8, 2022

Datatek said:
Is the aerial for the FOB receiver disconnected, does the FOB LED flash when the key is inserted in the ignition? If the LED does not flash, either the transponder coil in the ignition barrel has failed or perhaps the EKA and/or the immobiliser have been turned off in the BECM.

Aerial is as far as I know connected.

EKA, how do you turn it off? I have a nanocom and can disable it using it. But I don't recall seeing a way to turn it off. The keyfob is good (had it repaired by a bloke on ebay the other year), new case, new buttons and new battery. It was working fine. Will have to double check, but pretty sure nothing flashes when you inset the key in the ignition. Would it only do this on a key not sync'd or for any key? How can you check the barrel transponder?

In the past, the only way I have got the key(s) to work is by entering the EKA with the key in the door lock. This has worked 3 times in the past. But 98% of the time the door lock microswitches do not work and essentially prevent you entering the EKA.

Datatek · Dec 8, 2022

300bhp/ton said:
Aerial is as far as I know connected.

EKA, how do you turn it off? I have a nanocom and can disable it using it. But I don't recall seeing a way to turn it off. The keyfob is good (had it repaired by a bloke on ebay the other year), new case, new buttons and new battery. It was working fine. Will have to double check, but pretty sure nothing flashes when you inset the key in the ignition. Would it only do this on a key not sync'd or for any key? How can you check the barrel transponder?

In the past, the only way I have got the key(s) to work is by entering the EKA with the key in the door lock. This has worked 3 times in the past. But 98% of the time the door lock microswitches do not work and essentially prevent you entering the EKA.

I don't have a Nanocom so I cannot give exact details, but in the BECM pages you will see EKA and it's status. You can change the status from ON to OFF and write the change back. While you are doing it, you could turn off the immobiliser, saves a lot of hassle on the diesel but not sure on the V8. It's on the same BECM page as EKA.
You will then never heed EKA again and can use the car with FOB or key blade.

P38A What causes a keyfob to stop working?

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