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Audi A8L D3 3.0 Rear Light Fault & Vehicle Cutting out

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Audi A8L D3 3.0 Rear Light Fault & Vehicle Cutting out

Old 09-16-2018, 07:50 AM
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Default Audi A8L D3 3.0 Rear Light Fault & Vehicle Cutting out

Hi All,

can anyone help with a problem that I am having with my A8L D3 3.0 FSI where the car has had a lamp failure warning light appear & then with in a 6 hours of the car being parked the battery went completely flat.

The car car was started by breakdown service, and it was found that the Rear Stop Tail leds has failed.

We we drove home for 2 hours the car was fine, I tested the lamp when I got home and two leds in the stop tail were faulty, I replaced them tested the lamp and it worked fine.

I left the lamp lamp out over night & checked the car this morning and it started ok. I reinstalled the lamp, and took the vehicle for a drive and after 20 minutes the car lost power and stopped at a junction. The lamp warning light came on again and when I tried to restart it it would start but very quickly cut out! When I got to park the car safely I checked the rear light and the centre block of leds were not working.

I called breakdown services again, they came out and this time the breakdown service diagnosed the car & found the following issues:

Patrol found the following fault code/s:System : Engine control 1 - A0E / Simos 6 Status :P1602 - Power supply. Error Message : Undervoltage. Error sporadic. Status :P1653 - ABS control unit. Error Message : Read out fault memory. Error static.

When we started the car the stop and tail leds had all failed, but the indicator still works. I have driven the car home with the breakdown service following and the car got home without issue.

Has anyone had this occur before, could the rear lamp failure cause this issue and can anyone explain why this occurs as I have breakdown repair cover and if I can prove this lamp is the fault I can get the lamp replaced for free instead of 400 plus fitting.

Thanks in advance for your help.

Best regards


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Old 09-16-2018, 08:07 AM
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I can't tell if the symptoms and codes you are posting are more on the "cause" and direct issues side, or are really the effect and byproducts of a different underlying issue. That is, the same kind of electrical flakiness scattered around the car electronics is often simply the main battery failing. From the scan text you provided, that also seems like a generic scanner that is not Audi/VW specific. An Audi/VW scan that reaches all the modules and with specific code identifying text might tell more. Seeing the power management codes for example would help, and even a variety of simple codes that often show up in situations like this that show actual voltage. Buried in that engine code text already is a flag it is undervoltage, though it doesn't say how much. If it is in the ECU, it is likely in a variety of other modules too that a generic scanner isn't reaching.

Have you had the battery load tested? Voltage read of course, but also load testing to see if it can hold a strong charge. How old is it? Have you replaced it before?

Last edited by MP4.2+6.0; 09-16-2018 at 08:14 AM.
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Old 09-19-2018, 08:56 PM
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If any component is fried it can kill the power bus or pull it down until something smokes. My MMI module did this (created a power event) and when I pulled the tin can (module) I could have fried an egg on it. Just kidding - it was way too warm tho and codes showed a power issue.

So if your tail light is pulling mega current but not blowing the fuse it could take others with it.

And as above if the battery can't maintain a nice clean supply V+ then it would need to be replaced too. If a battery goes dead it needs to be smart charged for a good 24-48hrs to get back to full.
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Old 10-01-2018, 06:00 PM
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Brake light switch.
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