LED headlight fault [Resolved]

[Robert]

I am curious what fault codes VCDS would show up.

I can't see a resone why you couldn't replace your BCM(if it really is faulty) with a used revision B or C.
On these two variations keys can be paired with VCDS.
Additionally B and C can be upgraded(via firmware upload) to version D and key pairing procedure with VCDS remains.

 

[JimbobT6]

I am curious what fault codes VCDS would show up.

I can't see a resone why you couldn't replace your BCM(if it really is faulty) with a used revision B or C.
On these two variations keys can be paired with VCDS.
Additionally B and C can be upgraded(via firmware upload) to version D and key pairing procedure with VCDS remains.

Thanks Robert,
What diagnostics would be next I’d your think there is a possibility of it not being the BCM?

After today, my eggs were very much in that basket.

 

[JimbobT6]

Update… managed to get it on a VCDS today and will post the relevant pages that show faults.. welcome feedback as always

 

[JimbobT6]

Note - Ignore the fault ref dimmer control. That’s just because I removed the controller with facia panel to get to BCM

 

[Robert]

Can you paste in complete VCDS AUTOSCAN as a text?

 

[JimbobT6]

Can you paste in complete VCDS AUTOSCAN as a text?

I’ve only got the 11 page print out Robert?

 

[Robert]

Please don't use any service provided by that mechanic
And please don't follow any advice provided by him

 

[Robert]

Spoke to the mechanic at my mates garage when VCDS was being done and he thinks it could still be the local headlight power module. He said despite swapping that component with the other side they are programmed to VIN and the relevant side headlight so switching might not work to eliminate the module as a problem.

T6 LED power modules are not programmed to vehicle VIN.
Power modules are not assigned to any side of the vehicle.

He also thinks the power module issue could then be restricting the dip beam supply to 3-4v because the CAN fault error back from power module could be telling the BCM to reduce voltage.

BCM produces direct voltage output to headlam power module. The current consumed is being monitored and if that amp consumption falls out of range a corresponding fault code is registered by BCM. In some cases, like complete short circuit the BCM will completely switch off the faulty output. There is no CAN communication between headlamps and BCM.

Randomly he also said the headlight control rotary switch can go wrong and could be making the BCM fault the supply to left side dip beam. I’ll try swapping the switch with a mates and eliminate that as they aren’t VIN coded.

There is no fault code associated with the switch so it is very unlikely for this switch to be a problem.

 

[JimbobT6]

T6 LED power modules are not programmed to vehicle VIN.
Power modules are not assigned to any side of the vehicle.



BCM produces direct voltage output to headlam power module. The current consumed is being monitored and if that amp consumption falls out of range a corresponding fault code is registered by BCM. In some cases, like complete short circuit the BCM will completely switch off the faulty output. There is no CAN communication between headlamps and BCM.



There is no fault code associated with the switch so it is very unlikely for this switch to be a problem.

Thanks again Robert. Would be lost on this without you.

Just ref the headlight power modules, are you sure about them not being VIN coded.?
Only reason I ask is when I went to purchase one from local my VW parts dealer a few weeks ago they said it would be non returnable order from Germany as it had to be coded to my VIN.
I decided not to order it at the time and try swapping them first.

So in your opinion is still looking like the BCM?

Thanks

 

[Robert]

Have you disconnected your BCM output feed to your LHS low beam yet?
Have you checked resistance on your remaining section of wiring?

 

[JimbobT6]

Yes,

Did that last Sunday. Yellow / black nearside dip supply cable is good and resistance between BCM and headlight plug pin was 0.3 ohms.

Has to be BCM power output on that cable as everything has now been checked or replaced downstream from there.

From Sunday:-



Shall I just bite the bullet and buy a new BCM?

 

[Robert]

I couldn’t wait, so thanks for the encouragement.

Just done resistance check between nearside dip beam pin 2 output of BCM plug A to headlight connector pin 6 and I am getting
0.3 ohms, so loom must be all good??

View attachment 196099

Nearly zero resistance confirms continuity but doesn't exclude short circuit of this wire to the ground(or any other nearby and potentially damaged wiring).

I woud extract LHS low beam connector (PIN 2) from the BCM plug A.
Next I would clear all fault codes in the BCM and then read fault codes again.

If the fault codes are the same (00978 & 03645)
then your BCM is most likely faulty.
You could consider second hand units as well, maybe also revision C or B.

But if your fault codes are different(for example: LHS low beam open circuit)
then there is a problem with your wiring between BCM and RHS wheel arch.

 

[JimbobT6]

Nearly zero resistance confirms continuity but doesn't exclude short circuit of this wire to the ground(or any other nearby and potentially damaged wiring).

I woud extract LHS low beam connector (PIN 2) from the BCM plug A.
Next I would clear all fault codes in the BCM and then read fault codes again.

If the fault codes are the same (00978 & 03645)
then your BCM is most likely faulty.
You could consider second hand units as well, maybe also revision C or B.

But if your fault codes are different(for example: LHS low beam open circuit)
then there is a problem with your wiring between BCM and RHS wheel arch.

Thanks Robert. Will try that and provide an update.

 

[JimbobT6]

Thanks Robert. Will try that and provide an update.

I guess with pin 2 removed and LHS headlight unplugged I also could see if the yellow/black wire has continuity to ground?

 

[Robert]

Yes, correct.

 

[JimbobT6]

Yes, correct.

Just done this as don’t have ability to pull the pin from BCM connector.
Good news no continuity to earth on yellow/black LHS dip feed.

I could cut the wire back from BCM and reconnect everything.. Then if I get just the 3v on the supply with rest of circuit isolated I’ll know it’s the BCM??

Thoughts?

 

[Robert]

You are correct again

 

[JimbobT6]

You are correct again

Okay here we go….
Isolated LHS headlight yellow and black at BCM connector A.
Everything connected back together and codes cleared, I get exactly the same low voltage issues on yellow/black output from BCM wire.

That outcome plus loom from BCM to headlight checked for continuity to ground with no issue must now mean it’s a new BCM?

 

[JimbobT6]

I also get same fault codes during test with yellow/ black downstream system disconnected at BCM

 

[JimbobT6]

Randomly with headlight switch turned to off, I was still getting 2v output in yellow/black at BCM plug A (pin 2)??