skiracer

Yes I STFF......
2014 S8 75,000 mi.
This has happened twice in the last couple days:
1. Day 1: Came to a stop in drive to let out a passenger. Engine died, display showed "P", all other electronics/displays working but not responding. No response from the start button (yes foot on brake), no other controls would respond. Removed battery from key and waited a couple minutes (display showed no key) until the car fully shut down. Reinstalled the key battery and the car started right up and drove with no issues.
2. Day 2. Came to a stop to make a right turn. Car dies again. Display shows "P". I was able to get the MMI to turn off this time and the car shut down in 20 seconds or so. Restarted no issue and drove fine.

Ran a full VCDS scan of the car and came up with no codes that would relate to these failures. I don't know how old the battery is but the car starts fine immediately following these events and there are no other "weird" electronic behaviors others have attributed to low battery voltage. Any ideas from the brain trust? Other similar experiences? Really scary if this decides to die in the middle of traffic. I may replace the Varta battery just in case......

Andrew12

Assuming the "P" is for park? VCDS codes? What system are you using? Ross Tech has a forum as well. Maybe something on their site. Life is to short... Figure something out quick or take it to the dealer...

skiracer

Yes, P is for park. Ross Tech VCDS latest software. The only codes were for a TPMS warning (taken care of), a motor mount actuator (1294 - Actuator 1 for Drivetrain Mounts) and a window defrost flap. I've cleared all the codes to see what comes back.

Kabukie

Are you tuned? ECU/TCU tune?

A8L_New_England

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Space The Final Frontier? $hit That's Fukn Funny? Subtrochanteric Femoral Facture? WTF is STFF? Sorry if I'm the only clueless one.
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What did you say about the Auto Start/Start feature?
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OberklasseA8

Get the alternator tested. When was your last car battery replacement?

Andrew12

I always plug in a volt meter to the cigarette lighter. Prop it up in the passenger seat.
Would think a bad battery or alternator would generate multiple codes???
Good question on the mods!
Spill any beer in start stop switch?

skiracer

No tune- 100% stock tune no mods
STFF- Searched the f'in Forum.....
I do not know when/if the battery was replaced. At least 3 years ago, possibly the stock battery
No liquids spilled on center console (thank god....)
I will install a voltage readout in cig lighter and monitor that.
Thanks for the ideas guys!!

A8L_New_England

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If it's an eight year old battery, it would be prudent to change it whether it is part of this problem or not.
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skiracer

Update: After clearing all the codes via VCDS the car has not quit again but it's only been one day.
Voltage at startup = 13.8 Vdc
Steady state voltage while driving = 14.3-14.5 Vdc
Based on these readings I don't think the alternator is having issues, but if I can't find a date code on the battery I'll replace it preventatively.

One other note; after the two shutdowns I couldn't get the MMI to turn off or respond, so I have been driving with the MMI off. I can't fathom how a fault in the MMI could cause the issue I'm seeing but these cars are so complex electronically I guess anything is possible. I'll update this thread as I find out any more information for posterity.