LED headlight fault [Resolved]

[JimbobT6]

Hi all,

Would anyone have a dummies guide / schematic to the oem LED headlight system?

My 69 plate T6 has a developed a fault on the near side dip beam where it comes on for a few seconds and either goes off altogether or comes on and off every couple seconds..! Very annoying for the vehicle I front..

I’ve confirmed a sound battery supply and checked the obvious like main headlight plug connection.
I’ve also tried swapping the dip/full beam metal box power module between sides to see if the fault moves with it (the boxes that bolt to the side of the headlamps).

Have tried my Carista and I get the following codes:
00978 - Lamp for low beam left (m29)
And
03645 - capacity module for LED flood light left.

I thought the capacity module was the box that I swapped between sides, but is there something else I am missing here?

Any help greatly appreciated as it’s driving me insane. I am pretty handy with basic electronics, but these sensitive canbus SY systems have me stumped.

Thank you
James

 

[JimbobT6]

Update -
I think it might be a thermal issue as from cold the effected dip beam led comes on fine.
After approx 1min it then starts to pulse on and off. After approx 3mins of that it stays off.

Can you get the projector lamps out of the headlamp assembly?
I see on a drawing the lamps have a fan behind them… do these fail this causing a heat issue?

Thanks

 

[Robert]

Swap the power modules, left with right one.
By doing so you will verify whenever the problem is within the LED projector or in the power module itself.

 

[JimbobT6]

Swap the power modules, left with right one.
By doing so you will verify whenever the problem is within the LED projector or in the power module itself.

Thanks Robert,

If we’re talking about the same thing and the power modules are what I attached as a pic on my first post, then I’ve already done that and the issue did not change sides.

 

[Robert]

Missed that, sorry.
So replacement LED module is your solution, see below.

Maybe these will be useful as well.

View attachment 20526

View attachment 20536

 

[JimbobT6]

Missed that, sorry.
So replacement LED module is your solution, see below.

Thanks Robert, much appreciated.

Are the projector modules removable from the headlight in position? I’ve had a good look with a mirror and everything looks pretty well sealed.
The images you provided make it look like they do come out?

I really don’t want to have to remove the front end to be able remove the headlight if I can avoid it….

 

[Robert]

See video below.

And this is how I will be replacing faulty components.

Frame 4m39s is my favourite one.

 

[JimbobT6]

See video below.

That’s fantastic. Thanks Robert.
Makes complete sense now that you destroy the oem projector lamp access cover and then replace with a repair kit cover.

I’ll order some parts tomorrow

 

[JimbobT6]

Update - so far I’ve swapped dip beam power modules / ballasts and the problem did not switch sides. Stayed on the near side.

I’ve now also bought a brand new LED headlight thinking there is nothing left and the fault is exactly the same!!! The dip beam projector comes on initially, then after a few seconds starts to blink and then goes off with warning light also coming on dash…

Any other ideas? :-(

Thanks in anticipation

 

[JimbobT6]

Is there some sort of relay or unique power supply system that feeds the headlights?

Wondered if a relay starts to get warm or becomes intermittent and the canbus warning just drops power to the dip beam to protect everything….?

 

[Robert]

OEM T6 LED headlamps are fed directly from the BCM (no relays, no fuses in between).

First of all can you do some voltage measurements? See below.

Both low & high beam are 12V DC.
And when engine is running voltages are as follows.
View attachment 31755
View attachment 31756
Low beam is actually produced from the module with 3 LED chips and high beam module consists only 2 LED chips.
And this is the reason why the current consuption is lower on high beam and cable size was reduced accordingly.

In general LEDs are way more efficient than halogen light bulbs and therefore produce much more light with less wattage.

Second thing.
You could perform a simple experiment if you don't want to swap your headlamps or your LED projectors.
Just disconnect both headlamp plugs and connect 2 extending wires(approx 1.5m long each) to each plug(pin 5 and pin6) and run them across and connect to the headlamp socket on the other side(same for both headlamps).

Maybe there is an issue with your BCM.

By the way, can you also post your fresh VCDS Autoscan?

 

[JimbobT6]

OEM T6 LED headlamps are fed directly from the BCM (no relays, no fuses in between).

First of all can you do some voltage measurements? See below.


Second thing.
You could perform a simple experiment if you don't want to swap your headlamps or your LED projectors.
Just disconnect both headlamp plugs and connect 2 extending wires(approx 1.5m long each) to each plug(pin 5 and pin6) and run them across and connect to the headlamp socket on the other side(same for both headlamps).

Maybe there is an issue with your BCM.

By the way, can you also post your fresh VCDS Autoscan?

Thank you again Robert, was hoping you’d reply.
I’ll do the voltage checks and come back to you.

Ref the headlight cross connection suggestion, wouldn’t you agree I’ve just proved that in a different way by connecting a brand new oem headlight (in effect simulating a cross connection with the working offside light)?
With the symptoms exactly the same on the new headlight that would suggest the issue has to be with the BCM supply?

Would Carista give the required code detail as I don’t have VCDS at the moment?

Thanks again mate

 

[JimbobT6]

Defo supply issue. Only getting 3-4v on dip beam…

 

[Robert]

Engine running?

 

[Robert]

Defo supply issue. Only getting 3-4v on dip beam…

View attachment 195998

Measure also voltage in reference to battery negative.
So between pin 6 and battery minus.

 

[JimbobT6]

Engine running?

Yes, engine running.
I’ll do the same to batt neg and come back to you

 

[JimbobT6]

Same range of voltage when using batt neg..

Also tested main beam this time, which has been operating fine and voltage supports that.

 

[JimbobT6]

I am really kicking myself for not doing this supply check before I wasted time swapping headlight power modules and buying a new headlight..! :-(

 

[Robert]

Now you need to check continuity of your yellow/black cable.
Disconnect BCM plug A and
check resistance between pin 2 and headlamp pin 6.

 

[JimbobT6]

Now you need to check continuity of your yellow/black cable.
Disconnect BCM plug A and
check resistance between pin 2 and headlamp pin 6.
View attachment 196021
View attachment 196022

Thanks Robert,

Assume the BCM is under the drivers side of the dash behind headlight control switch?