VW T4 Forum - VW T5 Forum banner

1 - 7 of 7 Posts

·
Special Rapporteur
Joined
·
9,766 Posts
My understanding of it is that OBDII/EOBD is not primarily intended to report that sort of problem - all of the standard trouble codes are for engine/transmission operation and problem reporting.

VW may use non-standardised codes for that sort of issue but, if they do, it's not really a question of whether OBDII is smart enough, as it's just a standard way of signalling faults.

The real question is whether the body control module responsible for that lighting circuit is designed to monitor each individual bulb in that circuit. I don't have a specific answer, but in general I would guess that unless there's a good reason why it should... it won't. It's obviously cheaper to monitor several bulbs at once on one input than to have an input for each separate bulb - fewer ports required and a lot less wiring involved.
 

·
Special Rapporteur
Joined
·
9,766 Posts
Ok - to add some facts to the speculation above:

I just made the front offside indicator open circuit on my van and then checked for error codes.

OBDII/EOBD: no predefined error codes generated. If some non-standard ones were generated, the tool I used didn't see them.

VCDS: no less than 8 error codes, including horn, power mirrors and a few others. The reports only identified that ~one~ of the front indicators was not passing current - the body control module did not seem to be able to identify which one. As soon as the bulb was reconnected, all 8 codes could be cleared in one go.

So, in the example I tested, VW's built-in diagnostics seem to act as a very crude tool for finding electrical faults.
 

·
Registered
Joined
·
259 Posts
Discussion Starter #4
Ok- thnx for that ! I suspected it would work this way. Same reason reading a fault code can send the uninitiated on expensive red herrings come goose chase !
I wonder if you noticed that removing 1 bulb flicked out the whole side ( repeater and rear indicators) I wil have to open every light cluster to fix this, or maybe just a fuse? (T5.1 2011)
 

·
Special Rapporteur
Joined
·
9,766 Posts
I wonder if you noticed that removing 1 bulb flicked out the whole side ( repeater and rear indicators)
No, it didn't. Removing one bulb left all others on that side working at double flash rate. Also, the bulb failure warning on the dash resets itself every time you turn off the ignition (unlike some other faults such as ABS where it stays on for good or until cleared).

In your situation I would take out each bulb in turn and test independently (because occasionally they can fail short circuit), but if all bulbs are out on one side I would suspect a wiring fault somewhere (if you've had work done recently, possibly a trapped wire?).
 

·
Registered
Joined
·
259 Posts
Discussion Starter #7
Fixed....! Threatened to remove all fuses I could find, it started working again....! I do hope I aint got some pi**ball electrickery lying in wait for me !
Thnx guys- it's appreciated ! A:
 
1 - 7 of 7 Posts
Top