jas_r_1

I'll give it a shot - if it stops raining I'll put the LCI headlights back in on the weekend and await further instructions. But I still don't see how an a fault coming up by pressing the brake pedal will be fixed through a load resistor connected to the angel eyes.

B6S4

The i-drive is obviously having some kind of electrical error. The LCM controls everything between the brake lights, to the headlights to the side markers. Keep in mind the LCM is a basic solid state device which uses PWM to regulate alot of different lights. If there is an electrical problem on one of the circuits, it can transfer to others as the LCM is 1 unit. Without actually knowing how the internals of the LCM operate, all we can do is speculate.

You said you had bruce cables on the lights, for the time being, I would transfer back to the original lights. The best way to troubleshoot is to try 1 variable at a time. From some reading on this forum user are reporting failures of the bruce cables which cause the tail light errors.

In theory, all other things equal, when you swap to the LCI halogen headlights, the only thing that changes between the Pre-LCI lights to the LCI lights are the AE bulbs. In which case the LCM is providing the same amount of current to the AE circuit but only seeing half of the load resistance. On a component by component basis, where all other things have not changed, I can't see what else would be causing the issues. The LCM takes power from the car then distributes them to various locations through out the vehicle(different lights). When you apply the brakes, the tail lights pull current from the LCM causing them to illuminate. When the new AE lights are on, they are also drawing current at the same time as the brake lights, however, the LCM is not seeing proper resistance to that particular channel(assuming LCI lights are installed). If the LCM is calibrated for a certain resistance but is not seeing it, then a load is put on the LCM from the brake lights, it can cause a voltage drop across the entire LCM which would throw errors in various places.

Another thing to consider is that whenever the AE's are lit, so are the brake lights(running lights), its definitly possible that they are on conjoining circuits inside the LCM. Now depending on how the car behaves when the brakes are illuminated, this could be the root of the issue.

Sorry for all of the rambling, being an Electrical Engineer, these things intrigue me. I will try to run some simulations in the next day or 2 and try to see what I can find, but without knowing the schematics or how the LCM operates, all we can do is eliminate possible variations between the OE stuff and the non-OE stuff.

livefour2day

Thank you B6S4, for all your advice on this, if you want me to try anything please let me know what I need and where to wire it and I will be glad to test it, what you are saying is exactly what the guys on the Audi forum said to correct and air bag mod and it worked in that situation to.

jas_r_1, I am happy to test if you want to leave your headlights in, its up to you.

B6S4

Give me a couple days to look at the schematics and run some simulations, I have a busy weekend coming up so I won't have too much time to look at this as much as I would like to.

jas_r_1

"You said you had bruce cables on the lights, for the time being, I would transfer back to the original lights"

No LCI tail lights or Bruce's cables. I have the original lights in.

"Sorry for all of the rambling, being an Electrical Engineer, these things intrigue me."

Carry on rambling - if anything it's helping us get to the bottom of this. And as I don't possess any electrical knowledge, it's helping me understand what the potential issue is.

"jas_r_1, I am happy to test if you want to leave your headlights in, its up to you."

I think that might be a good idea - at least until we get a solution. I could probably make do with the rear light error whilst we get to the bottom of this but my wife can't stand the issue. I just need to check Sas will be happy to accept the cables if we cannot find a solution

B6S4

Looks like I was a little bit distracted before when doing calcs. If one of you guys don't mind and can actually locate a resistor around 14.5 ohm in a 10 watt or greater size, you could try wiring it in series (inline) with the angel eye bulb. This would compensate for the lower resistance of the new AE bulb allowing the LCM to see the proper resistance. The resistor could be inserted after the 2 AE wires are mergered into 1 but before the wire contacts the AE bulb itself.

I would give that a try and see how the car reacts, if this solves the issue, we know the car looks for resistance when checking for bulbs, if it does not work, then the LCM is looking for something else and we can start looking elsewhere.

jas_r_1

I already have a 25 watt 25 ohm resistor. Would this be ok or does it have to be 14.5 ohm?

livefour2day

B6S4 thanks I will go out this afternoon and get 2, i am so sure you are spot on with this as I had to go out this morning and it was quite cold I had the error this time front RIGHT without touching the brakes and it happened 4 or 5 times, then as it warmed by a couple of degrees it stopped, i am sure i read that cold weather affects the resistance, or am I being stupid ???

jas_r_1 no problem saves you pulling your lights out again and at least we will know if it works, but I am really sure B6S4 is spot on.

jas_r_1

Good luck - sounds like everyone is thinking it's the same issue so hopefully this will solve it.

Sas

Nope, no errors, only with (one) LED AE.
Build 09/2003 MY2004