Sync key after battery replacement

Karmann_65 · Dec 8, 2017

Hi all

The dash warning came up on the wifes 2015 Leon FR saying the key battery was on it's last legs.

After replacing the old battery with a tested new one, the remote unlock/lock no longer works. The little red LED on the key fob now only shines very dimly when a button is pressed.

Is this because the key needs to re-sync? What's the method to do this? Handbook says to "keep the key with the car" (does that mean in the door keyhole, ignition or just in close proximity to the car?) press the unlock button on the fob then manually turn the key in the drivers door to lock it within 1 minute. The key should now be synched.

Unfortunatley I set the alarm off late last night trying and had to dash into the house for the spare to shut it off.

Thought I'd ask here before anoying the neighbours again.

TIA

Walone · Dec 8, 2017

Karmann_65 said:
Hi all

The dash warning came up on the wifes 2015 Leon FR saying the key battery was on it's last legs.

After replacing the old battery with a tested new one, the remote unlock/lock no longer works. The little red LED on the key fob now only shines very dimly when a button is pressed.

Is this because the key needs to re-sync? What's the method to do this? Handbook says to "keep the key with the car" (does that mean in the door keyhole, ignition or just in close proximity to the car?) press the unlock button on the fob then manually turn the key in the drivers door to lock it within 1 minute. The key should now be synched.

Unfortunatley I set the alarm off late last night trying and had to dash into the house for the spare to shut it off. Thought I'd ask here before anoying the neighbours again.

TIA

If the light is dim with a new battery I would think that the new battery is faulty or wrong type or fitted incorrectly.

Karmann_65 · Dec 8, 2017

Walone said:
If the light is dim with a new battery I would think that the new battery is faulty or wrong type or fitted incorrectly.

With this in mind I tried another new battery (also with Chinese writing on it above the CR2025 number) and got the same result. No joy!

I put the "duff" CR2025 that came out originally (with no Chinese writing) and the car unlocks/locks straight away. With no re-sync.

Seems the key fob is particular to the brand of battery used. Both new batteries tested perfect with a meter.

Walone · Dec 8, 2017

Karmann_65 said:
With this in mind I tried another new battery (also with Chinese writing on it above the CR2025 number) and got the same result. No joy!

I put the "duff" CR2025 that came out originally (with no Chinese writing) and the car unlocks/locks straight away. With no re-sync.

Seems the key fob is particular to the brand of battery used. Both new batteries tested perfect with a meter.

The probable reason for the new batteries showing ok with a meter (I'm assuming the reading was around 3.2 volts) is that as soon as a load was put across the terminals the voltage would have taken a dive! Always used good quality branded batteries (Panasonic, Duracell, Sony etc.) I swear by GP batteries myself.

Karmann_65 · Dec 9, 2017

Walone said:
The probable reason for the new batteries showing ok with a meter (I'm assuming the reading was around 3.2 volts) is that as soon as a load was put across the terminals the voltage would have taken a dive! Always used good quality branded batteries (Panasonic, Duracell, Sony etc.) I swear by GP batteries myself.

Bought a GP battery today and it all worked straight away.

Thanks Walone

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Sync key after battery replacement

Karmann_65

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