pcmhacking.net

I have a series 3 VS ute with the 2 button key fob. BCM I bought brand new and had 2 new key fobs programmed to the BCM out of the car. This was done in Nov last year 2018.
What I have noticed is that on really hot days in WA like over 35 and if the car sits out in the sun, the central locking using the key fob will not work. If I unlock the car manually by hand with key in the barrel, central works fine. Dead lock works fine. Once the tempt cools, the remote central works.
Any ideas on what causes this???

VSRaptor wrote:I have a series 3 VS ute with the 2 button key fob. BCM I bought brand new and had 2 new key fobs programmed to the BCM out of the car. This was done in Nov last year 2018.
What I have noticed is that on really hot days in WA like over 35 and if the car sits out in the sun, the central locking using the key fob will not work. If I unlock the car manually by hand with key in the barrel, central works fine. Dead lock works fine. Once the tempt cools, the remote central works.
Any ideas on what causes this???

Sounds like the RF receiver module (which I understand sits under the centre of the dash and connects to the BCM, though I've not seen one in person) is drifting out of frequency (as compared to the fob) with temperature. Probably they mismatch to start with, and then drift further apart. Perhaps the RF receiver module has an ability to adjust its frequency slightly, I'm not sure.

Joe.

yeah probably drift as above. I have had similar issues with VPs but I was not sure if it was the receiver or the fob, luckily the VP fobs has a trim cap for rf tuning and I have always been able to re-tune the fobs to suit the car.

OK thanks for that, never even heard of it before, I thought the bcm unit itself had something like the receiver built inside of it.
Can this part be purchased still from Amcap? Does it require any linking to the bcm once replaced?

I rang amcap in Welshpool WA and according to them, there is no RF reciever. They think that the BCM has the reciever inside it as a one complete unit.
Anyone has a factory manual on this?

Nope it’s in the bcm! Only vt onwards have it up the top with the sun sensor.

What I noticed just now, after the car has been sitting for a few hours, when I went to unlock it, the interior light illuminated but no indicator flash. I locked it, the indicator flash came on once but late after the door locked and the interior light went out. I tried again to unlock and it gave 2 indicator flashes, interior light on, locking it, the indicator flashed once at the same time as the door locked.
Does this indicate a fault somewhere? Can the BCM be reset with a scan tool?

vs ss wrote:Nope it’s in the bcm! Only vt onwards have it up the top with the sun sensor.

Gottcha! Thanks for that clarification.

That's going to make tweaking the receiver module frequency more tricky, if it's built into the BCM. That's assuming the receiver has an adjustment capability.

The fob itself effectively doesn't have an adjustment capability, you'd need to remove its LC capacitor, replace it with a slightly lower value one and try to squeeze a very small trimmer capacitor in parallel with this.

Joe.

VSRaptor wrote:What I noticed just now, after the car has been sitting for a few hours, when I went to unlock it, the interior light illuminated but no indicator flash. I locked it, the indicator flash came on once but late after the door locked and the interior light went out. I tried again to unlock and it gave 2 indicator flashes, interior light on, locking it, the indicator flashed once at the same time as the door locked.
Does this indicate a fault somewhere? Can the BCM be reset with a scan tool?

The fact that there was any response at all to the fob button press - in this case, the flash of the indicators - tells me the problem is not one of mismatched transmitter/receiver frequencies.
Curious to know why a new BCM and matching fobs were purchased - was it because the old BCM exhibited the same problem?

picvrss wrote: The fact that there was any response at all to the fob button press - in this case, the flash of the indicators - tells me the problem is not one of mismatched transmitter/receiver frequencies.

I agree. The initial information and the latest information don't paint the same picture.

Yet "If I unlock the car manually by hand with key in the barrel, central works fine" makes this even more confusing, because it implies the locking mechanisms and the BCM control thereof are OK.

Joe.