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Discussion Starter #1
Over the last 2yrs I've been having a terrible time getting my 2007 Q7 TDI to start.

Symptoms:
- Long cranking (~8-10 seconds) on cold start
- Often have to try 2-3 times to start
- Large plume of white smoke out of the exhaust, but then normal idle without smoke.
- Starts fine with a hot/warm start

Conditions:
- Ambient Temperature irrelevant. Happens Hot/Cold, Summer/Winter.
- Vehicle must sit parked for longer than ~10 hours.

I spent many personal hours and a couple of thousand dollars (labour & parts) trying to diagnose the cause of the fault before I finally decided to take it in to my local Audi dealer's workshop.
The final straw came after I replaced the battery AND had the car sitting on charge overnight and it still had trouble starting.

My Diagnostics:
VCDS reported several "Function Limitation due to Under-Voltage" type events that correlated with the times that I tried to start the car, but nothing really appeared faulty.
I had "02072 - Control Module for Energy Management (J644), 004 - No Signal/Communication - Intermittent" errors that also correlated with the start times.

I had recurring errors from the Air Suspension level control, but I figured that the compressor was on its way out.
Code:
Address 34: Level Control  Labels: None
  Part No SW: 4L0 910 553 C  HW: 4L0 907 553
  Component: LUFTFDR.-CDC  H03 7660
  Revision: --H03001  Serial number: 15.1528-0096.2
  Coding: 0015520
  Shop #: WSC 31414 790 00001
  VCID: 2A511B3885E409A

1 Fault Found:
  01577 - Turn-Off due to Over-Temp
  001 - Upper Limit Exceeded - Intermittent
  Freeze Frame:
  Error Code: 68

Cause and Repairs:
The local dealer (Alto Audi @ Artarmon in Sydney) were fantastic. I spoke with the workshop manager (not just the service rep) and explained the history and everything that I'd done to this point.
I told him that he could have the car for as long as it took to fix the problem.

Turns out that there were TWO issues at play.
1) A faulty Air Suspension relay was staying energised even after the ignition systems shut down. This was causing nearly a 1A drain on the battery while the car should have been off.
2) An aging starter motor was cranking slowly and pulling more current than it should have, compounding the low battery problem and causing the long crank & starting issues.

The plumes of white smoke on startup was unburnt diesel flooding the system while trying to start.

A replacement starter motor and relay fixed the problems completely.

The dealer also advised me that the new battery that I'd put in less than 2 months prior was already faulty, despite their efforts to recharge it. The battery was only generating 480-490 CCA (Cold Cranking Amps) where it should have been generating 850 CCA.

Even though the car was now starting fine even with this "dead" battery, I organised a replacement battery under warranty just to be sure.

Hindsight:
In hindsight, the Level Control "Turn-Off due to Over-Temp" errors make a lot of sense now. The compressor must have still been running due to the faulty relay, which would have in turn caused all the "Function Limitation due to Under-Voltage" type events from the other modules when the battery drained.

Finally, I've got a car that has no trouble starting!
More importantly, I also have a happy wife who doesn't get embarrassed by flooding the neighbourhood with plumes of white smoke while sitting there trying to start the %$#@! car.

Hope this helps others.
 

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Dear TimU

I have the exact same problem with my Q7. Earlier i thought that it is the battery issue. I replaced the battery with a genuine audi battery.

After installing the new battery, the car started within 1-2 seconds of cracking and i could feel that the starter motor really cranked quickly with full power even after the fact that the car was parked for over a month without any starting.

When the next day i start the car, that took a cranking of 7-8 seconds, with the same white smoke plume out of exhaust.

And the 3rd day, the cranking would go on for like 10-12 second and i stopped trying as i knew that battery is not giving enough current and the cranking was sow.

My assumptions from your experience are;

1. Same fault with the starter motor
2. And battery current drain somewhere in the car.

Need your help to identify;

1. How do i find the status/health of starter motor? Any idea? Can VAG-COM do a check?

2. and how do i identify the car module/part responsible for potential battery drain? Though its not constant but i do get sometimes "under voltage" errors in many different parts of the car that i believe due to low battery current.

Any help would be highly appreciated.

Thanks

Talha
 
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