Golf R Tailight Fault Codes

May 22, 2016 1:45:55 GMT goose4485 said:

Has anyone seen these errors or have any idea what they mean?

B12BE15 - Left tail lamp bulb Open circuit/short circuit to B+
B12BF15 - Right tail lamp bulb Open circuit/short circuit to B+

B12BC15 - Left rear side marker lamp bulb Open circuit/short circuit to B+

Just scanned my Golf R and got these fault codes, not sure what they are.  Any ideas?

Goose: Hello - the DTCs (errors) in your post happen because each of the 35 exterior lamps on a mk7 are continuously monitored by what OBD11 calls the "Central Electrics" control module, but which many of us "older" folk call the BCM (Body Control Module). Lot's of stuff changed in the mk7: one of these changes was the fact that the car no longer has a fuse for each external lamp. Instead of traditional fuses, the BCM monitors the behaviour of each lamp for things like the lamp filament breaking (Open circuit), or a shorting-out of the lamp filament (Short circuit).  The BCM does this by measuring the amount of electrical current that flows in the lamp wire. I've deliberately over simplified my description- there's some other magic involved in the monitoring activity as well, such as digital to analogue converters and fault allocation tables in the module's memory, but this is way too-much detail for this response.

So,  looking at the 3 x DTCs in your post, it means that the BCM has activated the Left and Right tail light and it has either measured no electrical current flow (i.e. zero amperes), or it has detected too much electrical current flow for the type of lamp that it was told was installed in the car. The same result has occurred for the left rear side marker lamp (which I think is what we down here in the very deep south call "the left rear parking light").

Of course the more interesting question is why this has happened?  I'm always suspicious when I see these types of DTCs occurring simultaneously on both sides of the car. I guess that it is possible for the physical lamps on both sides of the car to experience a fault at the same time, but it's a little improbable!  More than likely, whenever I have seen this combination of DTCs, it normally means that the BCM has been re-programmed incorrectly to activate these lights and for some reason, the lights have not been able to electrically respond to the BCM's signal to turn-on. The result is no electrical current flow and hence the DTCs!

So - question for you. Have you done any tweaks to the rear tails?

Don