Chris Black

I'm beginning to wonder if facelifting my Q7 was such a good idea after all.

I purchased OEM facelift taillights and installed them, with no problem. I already had changed the stock halogen headlights to HIDs. The front turn signals were also replaced with OEM led turn signals.

The final part, which has now seemingly caused the malfunction, was changing the halogen license plate lights to HIDs.



Now here's the problem: I found out after about 4 minutes of idling (and I'm assuming the same happens while driving at night), the rear taillights, as well as the rear license plate lights flicker about 3-4 times, then shut off. What's stranger even are my headlights and front turn signals are unaffected. So the rear shuts off, while the front is fine.


I've noticed the battery (which I replaced not but 6 months ago) runs perpetually low. When I go to battery monitoring on the MMI, it always has me at 10%.




So what the heck is going on? Did switching everything from factory halogens and the first gen tailights to all HID/LED/facelift equipment overload the battery? I can't figure out what the hell is going on. I'm thinking about ripping the gate off the trunk and checking the wiring to the taillights and license plate lights. What's the problem?

D3Audi

This is called Cold Diagnostics, unfortunately I don't know if it can be turned off, do you have VCDS? It could be possible to turn it off. All 2007-2009 pre-facelift Q7s have this issue when upgrading to LED lights. I recently upgraded a couple of my exterior bulbs to LED bulbs with resistors, and they flash upon start up, then flicker every 30seconds to 1 minute. It is the cold diagnostics system checking to see if a bulb is burnt out, but since LED lights use such a low resistance level to turn on compared to halogen, you can see the flash, and if you don't have resistors, it will send that pulse of electricity to the bulbs but the car will think it has an open circuit (burnt bulb) so it cuts power to those lights. I assume the rear lights in your bumper turn on when the rear lights are turned off? Also, I'd be willing to bet your front turn signals flash as well. at night, leave the car running, and go stand outside the car and watch the lights, they will most likely flicker and flash. I would disconnect your LED bulbs until you find a way to turn off cold diagnostics, the cold diagnostics will ruin the diodes in your bulbs. And your LED lights are expensive so you don't want that to happen. And is the car having trouble starting? Because if it is starting normal, then I wouldn't worry about the battery gauge, mine says 10% after I start it sometimes. Not a big deal.

Chris Black

D3, yes you're exactly right - the rear lights in my bumper are still on even when my tail lights turn off.

Car starts normal. Now to your point about disconnecting my LED bulbs - I already sold my old turn signals / tail lights, so I'm SOL. I'll ask my mechanic about VCDS

D3Audi

Did you install resistors for your tail lights and turn signals?

Chris Black

For my tail lights I'm literally running the lights directly to the power from the rear 12V - no resistors or fuses (it was fine until I switch my license plate lights).

License plate lights might be getting switched back - looks like this has triggered the same problems for others - read the 3rd post in this thread:

https://www.audiworld.com/forums/a6-...stics-2821500/

D3Audi

You could try that, you need to find a way to disable cold diagnostics though, because it is going to ruin your LEDs, including your front turn signals. And for the LED tail lights, what do you mean they are wired to 12v power? You didn't purchase the adapter on eBay? Are the lights always on? Because that 12v sends a constant power, the 12v outlets don't turn off when the vehicle is off. That could explain your battery.

D3Audi

Adapter Control Unit for Original Facelift LED Taillights Taillights for Audi Q7 | eBay

Chris Black

Wow yes that explains it.

This was the install video I used - you'll see exactly what I did if you skip to about 45 seconds. He first shows the option of plugging it into a fuse but then just hardwires it to the 12v. I guess I need to use a fuse then? I already have the control unit ...

Chris Black

The lights however are not always on. They turn off when I turn the car off.

Chris Black

Forgot the install video -