TimU

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.

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.

DEE1226

Hi Timu

Thanks for the write up. My battery drain issue in our 2007 Q7 has been causing my wife such problems with comments like "sell this junk car" and " how embarrassing a Q7 and I need to keep jump leads in the car" is putting it mildly.

I think I too may have the relay problem as my new battery dies randomly and only since reading your post have I realised the vcds scan of the car brings up the level control turn off due to over temperature at the same time.

I will get the relay from Audi and see if this fixes the issue. Do you know where it is located in the car? Mines right hand drive and I have read it is in the engine bay on the early models.

B490MTL

I'll look in my Bentley tonight, you do have a few relays under the dash too.

TimU

The relay seems to be under the dash according to this:
Location of J403 air-suspension relay

DEE1226

According to this it maybe in the engine compartment. Seems like I will just have to try both location.

Location of air-suspension compressor relay for 2007 AUDI Q7 3.0

TimU

Interesting. Keep up updated please?

DEE1226

Car has extended warranty so thought why not leave it to the experts?!

The car has now been in with Audi since Monday 17th. I informed the service guy about this post and the relay only to be told this had been changed on the last visit about 2 months back, following which the battery drain issues started!!

They ordered a new air suspension pump and fitted this on Friday telling me they could not find any battery drain problems and battery was fine. Just before I was due to pick the car up, guess what the battery drained.

Still waiting to hear back...at least it happened whilst still with them.

DEE1226

Audi changed the relay after being pointed in that direction again by myself and hey presto all is well.

A month on and a holiday in between the car is still starting perfectly first time. No more battery drain.

Thanks again to OP for solution.

Waj786

Hi, im new to the forum, i've also been having the same problem as above, could someone please tell me how much the Air suspension relay would cost?

Thank you

TimU

Around $30-40 for genuine VAG part number 4H0951253A.
It's a pretty standard 40A relay, so I'm sure you'll be able to find something generic for less.